Monodominance at the rainforest edge case study of Codiamackeeana (Cunoniaceae) in New Caledonia

Thomas IbanezAC and Philippe BirnbaumAB

AInstitut Agronomique neacuteo-Caleacutedonien (IAC) Diversiteacute biologique et fonctionnelledes eacutecosystegravemes terrestes BPA5 98848 Noumeacutea New Caledonia

BCIRAD UMR AMAP 34398 Montpellier FranceCCorresponding author Email ibaneziacnc

Abstract Monodominance is unexpected in tropical forests which usually exhibit rich and diverse flora Mechanismsleading to monodominant forest are commonly discussed within the theoretical framework of forest succession One of thecentral issues formanagers is to determinewhethermonodominance is a non-persistent step in the successionofmixed forestor a late successional state that persists for several generations Early successional (post-external disturbance)monodominantforests are likely to be themost common but studies have focussed on late successional ones (without external disturbance)Here we investigate monodominance in Codia JRForster amp GForester (Cunoniaceae) in New Caledonia Codia forestscharacteristically occur either as patches within a matrix of mixed forests or as a narrow belt located at the interface betweenmixed forest and open vegetation We test the hypothesis that monodominance in Codia is an early and non-persistent stepin the secondary succession towards mixed forest through a case study of C mackeeana Spatial patterns of canopy leveldominance and the regeneration pool in a large C mackeeana population as well as along five transects from savanna tomixed forest support our hypothesis Establishment of C mackeeana likely allowed a quick closure of anthropogenicsavannas followed by a slow recovery of diversity towards mixed rainforest

Additional keywords forest succession savanna single-species-dominant forests tropical forest

Received 1 April 2014 accepted 20 June 2014 published online 21 August 2014

Introduction

The co-occurrence of forests dominated by a single species(hereafter monodominant forests) and species-rich forests intropical ecosystems has long aroused curiosity of ecologistsConnell and Lowman (1989) provided a broad definition ofa monodominant forest a forest is monodominant when over50 of the stems basal area biomass or cover of canopy treesbelongs to one species From the most influential early papers(Connell and Lowman 1989 Hart et al 1989 Hart 1990) to arecent review (Peh et al 2011) the mechanisms leading tosuch monodominance have been discussed in the theoreticalframework of forest succession One of the central issues formanagers is to determine whether monodominance persiststhroughout generations preventing the succession towardsmixed forest or alternatively whether monodominance occursduring only one generation as a step in this succession (egmonodominance Type I and II sensus Connell and Lowman1989)

The following two general models of monodominanttropical forest have emerged from the literature (1) non-persistent early successional monodominant forest relying onpost-disturbance (eg fire or cyclone) establishment of shade-intolerant species able to disperse over large distances and(2) persistent late successional monodominant forest relying

on the establishment of poorly dispersed and shade-tolerantspecies without disturbances (Hart 1990) Recently Newberyet al (2013) suggest that these models can be placed in a two-way table of in situ or ex situ (re)establishment versus presenceor absence of large disturbance According to this newframework non-persistent early successional monodominantforests are more likely to result from ex situ establishmentunder external large disturbance while persistent latesuccessional monodominant forest are more likely to resultfrom in-situ establishment without disturbance Thisframework is completed by a third model named lsquotransientdominancersquo in which persistence relies on the in situ (re)establishment after large external disturbance of shade-intolerant and poorly dispersed species Indeed even if thedominant canopy species cannot establish under its own shade(ie seedlings observed in the undergrowth) monodominancecould persist if there are disturbances that allow the species toregenerate in large gaps

Although non-persistent early successional monodominantforests are likely to be the most common model in the tropics(Hart 1990 Peh et al 2011) most studies have focussed on latesuccessional monodominant forests eg in Brazil (Nascimentoand Proctor 1997) Cameroon (Newbery et al 2000) or Guyana(Henkel 2003 Fonty et al 2011) In their review Peh et al

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Australian Journal of Botany 2014 62 312ndash321httpdxdoiorg101071BT14062

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(2011) suggest that mechanisms leading to early successionalmonodominant forest are more straightforward (ie regenerationafter large-scale disturbance) than mechanisms leading tolate successional monodominant forest (called lsquoclassicalmonodominancersquo) which may be multiple and much morecomplex Indeed at a global scale although late successionalmonodominant species share some traits (eg poor dispersaland shade tolerance) multiple mechanisms involving differentsuites of traits in both adult and juveniles stages as well aspositive feedbacks between adult and juveniles may lead tomonodominance (Torti et al 2001) Nevertheless note that inmost studies (eg Marimon et al 2012 in Brazil) the persistenceof monodominant forest is inferred from simple fieldobservations (ie presence of recruitment in the undergrowth)rather than really tested (but see Newbery et al 2013 Readand Jaffre 2013)

In New Caledonia forests monodominated by Nothofagus(Nothofagaceae) were described as occurring on ultramaficsubstrates at the interface between maquis and mixedrainforests (Read et al 1995) Since then strong evidence hasemerged for the importance of large disturbances such as firesor cyclones but not for other biotic or abiotic factors indetermining the distribution and dominance of Nothofagus(Read et al 2000 2006 Chatain et al 2009) In sum forestsdominated by Nothofagus are likely to be long early steps in thesecondary succession towards mixed rainforests (Read andJaffre 2013) Most Nothofagus forests result from in situestablishment after large disturbances whereas ex situestablishment after a disturbance in a mixed rainforestalthough possible is less likely because of poor dispersal ofNothofagus (J Read pers comm) Many other cases ofmonodominance of native or non-native species punctuate thelandscapes of New Caledonia but have received less interest(but seeMcCoy et al 1999 formonodominance inGymnostomaRigg et al 2010 for monodominance in Araucaria)

Here we focus on New Caledonian forest patches dominatedby a member of the endemic genus Codia JRForster ampGForester (Cunnoniaceae) (14 species Hopkins 2005Hopkins et al 2007) Codia has a large distribution all alongthe main island (Grande Terre) and also occurs in the otherislands of the archipelago (httpwwwendemiancflorefiche298html accessed 25 June 2014) This genus encompasseswind-dispersed shrubs small trees and more rarely large treesMost Codia species grow on either ultramafic or non-ultramaficsubstrates although some species grow on both substrates types(Pillon et al 2009)Monodominancehasbeenobserved in severalspecies including C albicans C discolor C incrassata andC mackeeana but this phenomenon is poorly documented (butsee Ibanez 2012 for C albicans) Across the New Caledonianplant inventory and permanent plot network (Ibanez et al 2014)Codia has never been inventoried as an isolated individual butmore often as dominant species

Here we investigate monodominance in Codia through thecase study of C mackeeana HCHopkins amp BFogliani We testthe hypothesis that monodominant C mackeeana (CM) forestis an early and non-persistent step in the process of secondarysuccession from open areas (here savannas) toward mixedrainforest Specifically we ask whether (1) patch populationsof CM within matrices of mixed rainforest arise from

colonisation of savannas and (2) will mixed rainforest succeedto CM monodominant forest patches

Materials and methodsStudy areaNew Caledonia is a biodiversity hotspot (Myers 1988Mittermeier et al 2004) located in the south-western Pacific~1500 km east of Australia and 2000 km north New Zealand(between 20ndash23S and 164ndash167E) This archipelago harboursa unique flora (Morat et al 2012) and rainforests areparticularly rich and diverse (Ibanez et al 2014)

CM is a tree growing on non-ultramafic substrates in tropicalrainforest between 350 and 550m (Hopkins et al 2007) Mostof the known specimens are from the region of Farino ColdrsquoAmieu and Boghen valley The study area is located in theprovincial park Parc des Grands Fougegraveres (ndash213602400S1654501100E) located in the vicinity of Farino on the westernside of the New Caledonian central mountain range between300 and 700m asl (Fig 1) This park was created in November2008 receives an annual rainfall of ~1800mm (METEO-FRANCE 2007) The 4535 ha of the park consists mainly oftropical rainforests (92) and savannas or secondary thicketsdominated by Melaleuca quinquenervia (MQ 6) and Pinuscaribea plantations (2)

Data collectionPopulations of CM observed in Parc des Grands Fougegravereswere arranged in two different spatial configurations theyform either patches within a matrix of mixed tropical rainforestor linear belts at the interface between savanna and mixedtropical rainforest We hypothesised that patches included inmixed forest matrix result from the expansion of CM frommixed forest edges toward savannas To characterise thedominance of CM and test this last hypothesis we appliedtwo complementary sampling designs The first (hereafterSAMPLE-1) aims to describe the dominance of CM in a patchand to test its persistence and the second (hereafter SAMPLE-2)aims to test the ability of CM to expand from forest edgestoward savannas If our hypothesis is true we should observethat (1) CM establishes in savanna (2) mixed forest speciesestablish in CM forest and (3) the dominance of CM does notpersist in the undergrowth and so decreases with increasing ageof the population

SAMPLE-1 a large patch of CMcovering ~6 hawas delimitedusing both GPS tracking in the field and digitalisation on Googlesatellite layer using the geographical information system QGIS(QGIS Development Team 2013) and the OpenLayers plug-inDigitalisation was facilitated by the homogeneity of the canopygrain of such monodominant vegetation compared with thesurrounding mixed tropical rainforest (eg Degagne et al2009) We then applied a regular 20m 20-m grid on theidentified area of interest (300m 400m located between~400 and 500m asl) encompassing the CM population andits neighbouring matrix of mixed tropical rainforest Finally werandomly selected 37 grid nodes as sampling points (32 in CMand five in mixed tropical rainforest) For each of these samplingpoints (Fig 1) we inventoried all trees with a diameter at breastheight (ie at 13m DBH)10 cm DBHwithin a radius of 10m

Monodominance at the rainforest edge Australian Journal of Botany 313

(ie in an area of 314m2) and all small trees (5 DBH lt 10 cm)within a radius of 2m (ie in an area of 126m2) In this last areawe also counted the number of seedlings (50-cm height andDBH of lt5 cm) in three species groups CM MQ or otherspecies This sample design allowed us to analyse the spatialvariability of the dominance of CM and species richness

SAMPLE-2 two large savanna patches located nearSAMPLE-1 were selected to study belts of CM at the interfacewith mixed rainforest Field survey confirmed that most ofthese interfaces consist of narrow CM populations (~20ndash60-mwide) Five transects were positioned across these interfacesperpendicularly to forest edges (closest transects were 150mapart from each other) The lengths of the transects were definedas the width of the population of CM canopy-level trees(DBH10 cm) plus 20m toward savanna and 20m towardmixed tropical rainforest Thus each transect consisted of thefollowing three compartments the savanna the CM populationand the mixed forest The length of the transects ranged between60 and 100mAlong the entire length of transects we inventoriedall trees (DBH10 cm) in a 10-m strip all small trees (5 DBHlt10 cm) in a 5-m strip and all seedlings (50-cm height andDBH lt5 cm) in a 1-m strip Seedlings were classed as CM MQor other species Each plantrsquos position was recorded along thelength of the transects with measuring tapes (with ~5-cmaccuracy)

Field sampling occurred in OctoberndashNovember 2012 and2013 Most species were identified in the field but in caseswhere identity was in doubt samples were collected andidentified by comparison with the collection of voucher

specimens in IRD herbarium of Noumeacutea Plant names followFLORICAL nomenclature (Morat et al 2012)

Data analysesThe dominance of species was evaluated using the relativedensity (RDENS) of canopy-level trees (DBH10 cm)defined as the ratio between the number of stems of a givenspecies and the total number of stems A species is consideredmonodominant when RDENS is 05 (Connell and Lowman1989) As suggested by Connell and Lowman (1989) weadditionally computed relative basal areas (RBA) to expressdominance based on biomass RDENS was computed for allspecies but we paid special attention to the dominance of CMand MQ whereas other species were analysed together MQ isthe dominant tree species in New Caledonian savannas and isshade intolerant and unable to establish in forest (Serbesoff-King2003) MQ trees die during forest recovery (Ibanez 2012) Thuswe make the reasonable assumption that the presence of dead orliveMQ trees in forest indicates the past presence of savanna (egIbanez et al 2013c)

In SAMPLE-1 these statistics were computed for eachsampling point separately In SAMPLE-2 we first computedthese statistics for each compartment identified in the field (iesavanna CM population and mixed forest) before using amoving window to analyse how they vary along transects Weused a 5-m-wide window with a 1-m step

In both samples we also analysed the relationship betweenthe relative density of CM (RDENSCM) population DBH

0 25 5 km

Study area

Study area

Parc des Grandes Fougegraveres

Farino

Noumeacutea

New Caledonia(Southern Province)

-21

-22

166

167

Park entrance

SavannahForestLarge C mackeeana population

Sampling pointsTransects

0 100 200 m

Pic Vincent

T5

T3

T4

T2T1

Pat

hway

N

Fig 1 Location of the study area in New Caledonia (Parc des Grandes Fougegraveres) and description of the sampling design The sampling design consists in 37sampling points in a large Codia mackeeana population surrounded by forest and five transects crossing the forestndashsavanna edges in two adjacent savannas

314 Australian Journal of Botany T Ibanez and P Birnbaum

structures recruitment pools (amount of small trees andseedlings) and species richness using linear relationships Inthe absence of growth-rate data we inferred the age of thepopulations using the distribution of DBH to study thedynamics of CM Although growth rates may differ accordingto the environment (eg savanna vs forest) we assumed thatthe distribution of the DBH is positively correlated with the ageof the individuals hence older CM populations should exhibitlarger DBH Species community patterns in SAMPLE-1 werecomputed using non-metric multi-dimensional scaling (NMDS)using the R package vegan (Oksanen et al 2012) All statisticsanalysis was performed using the R 2152 environment forstatistical computing (R Core Team 2012)

Results

Dominance of the canopy by C mackeeana

Across all samples almost 40 of the 2004 inventoried canopy-level trees (DBH 10 cm encompassing trees ferns and palms)belonged to C mackeeana (CM) In SAMPLE-1 when CMwas

present (32 over 37 points) its relative density (RDENSCM)ranged from 002 to 097 (044 030 sd in average) andRDENSCM was 05 (ie CM monodominance) in 14 of 32points (Fig 2) Considering the biomass the dominance ofCM was even more important with RBACM ranging from 004to 099 (060 030 sd in average) and RBACM05 in 20sampling points

No other species exhibits monodominance The secondmost abundant tree species was the savanna remnant treeM quinquenervia (MQ) Live MQ occurred in 12 samplingpoints (18 taking into account dead trees) mainly located alongthe ridges and showed low relative densities (RDENSMQ

ranged from 002 to 029) and basal area (RBAMQ rangedfrom 001 to 057) The maximum RDENS and RBA valuesobserved from all other forest species never exceeded 05 andranged from 001 to 049 (015 009 sd in average) and from001 to 041 (014 011 sd in average) respectively

The CM populations occupied 20ndash60m (ie 200ndash600m2) ofthe five studied transects (SAMPLE-2) RDENSCM ranged from043 to 068 (053 009 sd in average) and RBACM ranged

Longitude (DD)

Latit

ude

(DD

)

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

Codia mackeeana Melaleuca quinquenervia Max(other species)

Relative density

Relative basal area

1657635 1657645 1657655 1657635 1657645 1657655 1657635 1657645 1657655

Value 0 025 050 100times

(a) (b) (c)

(d) (e) (f)

430 430 430

430 430

450 450

460 460

470 470

430 430

430 430

440 440

440 440

430 430

430 430

420

420

440 440

450 450

460 460

470 470

440

440

440 440420

420

440 440

440 440

430

440

440450

460

70

430

430

440

440450

460

430

440420

430 440

440

440

440

440420

Fig 2 Spatial variation in (andashc) relative density and (endashf) relative basal area of Codia mackeeana Melaleuca quinquenervia and maximum values for allother species pooled together Point size is proportional to values of relative density or relative dominanceBlackpoints indicate valuesgt05 (iemonodominance)and crosses null values Contour lines represent elevation isoclines (10m)

Monodominance at the rainforest edge Australian Journal of Botany 315

from 052 to 067 (060 008 sd in average) Moving windowanalysis highlighted heterogeneity in these populations(Fig 3andashe) RDENSCM ranged from 02 to 1 and the areasidentified as monodominated by CM (ie RDENSCM 05)were smaller (37ndash81 of the area) The transition fromsavanna to the CM population was very sharp whereas thetransition from CM populations to mixed forest was moregradual

In both samples the dominance of CM mainly reflected ahigh density of small stems In sampling points dominated byCM (SAMPLE-1) the median DBH of CM was 197 cm (range

100ndash643 cm) while in other sampling points the median DBHwas 299 cm (10ndash914 cm) (Fig 4) A similar pattern wasobserved along transects (SAMPLE-2) with a high density ofCM small stems (Fig 5) Most (nearly 75) CM trees wereinventoried in the first 20m behind the savannandashforest edge withmedian DBH of 141 cm Overall the median DBH increasedlinearly with the distance from the savannandashforest edge

Scarce recruitment of C mackeeana in the undergrowth

In total 53 small trees (ie 5 cmDBH lt 10 cm) and 1382seedlings (ie height50 cm and DBH lt 5 cm) were

Transect 1 Transect 2 Transect 3

Transect 4 Transect 5

Position along the transect (m)

Position along the transect (m)

Rel

ativ

e de

nsity

Rel

ativ

e de

nsity

TreesS

mall trees

Seedlings

TreesS

mall trees

Seedlings

OtherCMMQ

OtherCMMQ

For

est

Savannah

OtherMQ

CM

(a) (b) (c)

(f ) (g) (h)

(k) (l ) (m )

(d )

(i )

(n ) (o )

(j )

(e )

Fig 3 Relative density profiles (andashe) of canopy-level trees (diameter at breast height (DBH) 10 cm) and (fndashj) undergrowth-level small trees(5 cmDBH lt 10 cm) Lines represent smoothing values of relative densities of Codia makeeana (CM full black lines) Melaleuca quinquenervia (MQfull grey lines) and other species (Other dotted black lines) Grey areas highlight areas where CM is considered as monodominant (RDENSCM gt 05) Bottomgraphs (kndasho) represent the locations of CM MQ and other species seedlings (50-cm height and DBH of lt5 cm) along the transects

316 Australian Journal of Botany T Ibanez and P Birnbaum

inventoried in the undergrowth of SAMPLE-1 This regenerationpool was by far dominated by forest species (94 of the smalltrees and 99 of the seedlings) Regeneration of CM was scarce(3 small trees and 19 seedlings located in only 3 and 7 of the 37sample points respectively) and neither MQ small trees norseedlings were observed in the undergrowth No clearrelationships between the characteristics of the CM canopy-level population and regeneration pool were detected

In contrast in SAMPLE-2 many CM small trees wererecorded in the undergrowth of the CM canopy-levelpopulation (Fig 3fndashj) Nevertheless compared with thecanopy-level population the extent and the relative dominancein the undergrowth decreased as the dominance of other forestspecies increased Only 10 of the 393 inventoried seedlingswere CM (81 were forest species and 9 were MQ) CMseedlings were found both under CM canopy and in opensavanna (up to 172m in front of the forest edge) at similardensities (015 seedlings mndash2 on average Wilcoxon testP-value gt005) Conversely MQ seedlings were found only insavannas (Fig 3kndasho) Seedlings of forest species occurredall along transects and their number increased significantly(chi-square test P-value lt0001) from savanna to mixed forest

(8 in savanna 36 in the CM population and 56 in themixed forest)

Species richness and species composition patterns

Despite the dominance of CM 121 taxa belonging to 50families were identified (24 trees were not identified seeAppendix S1 available as Supplementary Material for thispaper) In SAMPLE-1 canopy-level species richness wasnegatively correlated with RDENSCM (Fig 6a b) In samplingpoints where CM occurred species richness ranged from 3 fora RDENSCM of 094 to 23 for a RDENSCM of 004 whereasspecies richness reached up to 30 in adjacent mixed forestOverall the spatial pattern of species richness in SAMPLE-1suggested that species richness increased from CM populationslocated on the ridges and upslope to mixed rainforest locateddownslope This pattern was highlighted in the SAMPLE-2with species richness increasing from savanna located upslopeor on the ridges to mixed forest located downslope (Fig 7) Theprofiles of species richness and cumulative number of specieswere not affected by the CM population

Interpreting floristic composition was difficult because ofthe overall rarity of species in both samplings Only 31 specieswere represented by more than 10 trees and only 23 of themwere inventoried in both samplings In SAMPLE-1 NMDShighlighted gradual changes rather than clearly distinct plantcomposition Distribution of the most common species alongtransects (Table 1) suggested that no species were able to growin all three compartments of our transects However mostspecies occurred either in savannandashCM interface or theCM-mixed forest one As a result the canopy between the

(a) (b)10

06

04

02

0

RD

EN

SC

M250

200

150

100

50

0Fr

eque

ncy

10 20 30 40 50 60 70 80

DBHCM

08

20 40 60DBHCM

80 100

Fig 4 Populations size structure of Codia mackeeana trees (CM) inSAMPLE-1 (a) Diameter at breast height of CM (DBHCM) as a functionof the relative density of CM (RDENSCM) points represent the median valueand bars the 1st and 3rd quartiles intervals (the grey tone of the points isproportional to RDENSCM) Median values were significantly smaller whenRDENSCM05 (Wilcoxon rank sums test Plt 0001) (b) Histogram ofthe distribution of DBHCM all sampling points for which RDENSCM05pooled together

20

60

50

40

30

20

10

40

Position along the transect (m)

DB

HC

M

60 80

T1T2T3T4

T5

Fig 5 Size distribution of Codia mackeeana (DBHCM) according tothe position of the trees along the transects (Pearsonrsquos r= 034 P-valuelt0001) Dark solid line represents linear quantile regression for q= 05(median y= 020x+ 847) and grey polygon represents the intervalbetween the linear quantile regressions for q= 025 and q= 075 Thevertical black line represents the forestndashsavanna edge

Monodominance at the rainforest edge Australian Journal of Botany 317

savanna and the mixed forest although dominated by CMconsisted of a mixture of pioneer species such Myodocarpusspecies (mostly found close to the savanna) as well as foresttree species such as Garcinia virgata Plerandra pancheri orCalophyllum caledonicum (mostly found close to the mixedforest) Additional small trees such as Guioa glauca orDiospyros olen enriched the undergrowth

Discussion

Monodominance of C mackeeanea a step in thesuccessional process

Our results suggest that the observed CM populations constitutean early and non-persistent step in the process of successionfrom savanna to mixed tropical rainforest The studied patch of

1657635

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

1657645

Longitude (DD) 1-RDENSCM NDMS11657655 00 02 04 06 08 10 ndash04 ndash02 00 02 04

Latit

ude

(DD

)

R2 = 072lowastlowastlowast FOR

20

15

10

5

Spe

cies

ric

hnes

s

04

02

00

ndash02

ndash04

ND

MS

2

(c)(b)

y = 41 + 148

lowast x

MQ

CM

Stress = 015(a)

430

440450

460

470

430

440420

440

Fig 6 Distribution of species richness and relationship with relative density ofCodia mackeeana (RDENSCM) in the SAMPLE-1 point size is proportional tospecies richness and point colour is proportional to RDENSCM (linear grey scales white for RDENSCM= 0 and black for RDENSCM= 1 (a) Map of samplingpoints contour lines represent elevation isoclines (10m) (b) Linear relationship between species richness andRDENSCM (sampling points where RDENSCM= 0were removed) (c) Ordination of sampling points using non-metric multidimensional scaling (non-metric multidimensional scaling 2D-solution) CMindicates points where RDENSCM05 MQ points where alive Melaleuca quiquenervia were inventoried but no C mackeeanea and FOR mixed forestpoints where neither C mackeeanea nor M quinquenervia were inventoried

Transect 1

Transect 4 Transect 5

Transect 2 Transect 3

0 10 20 30 40 50 60

0 20 40 60 80 100

Position along the transect (m)

0 10 20 30 40 50 60

0 10 20 30 40 50 60 0 10 20 30 40 5070

40

30

20

10

0

40

30

20

10

0

Spe

cies

ric

hnes

s amp

cum

ulat

ive

num

ber

of s

peci

es

Fig 7 Smoothed local species richness (black lines) and cumulative number of species (dotted lines) along the five studied transects (trees and small treespooled together) Vertical black lines represent first and last inventoried Codia mackeeana (CM) along the transects and grey areas represent areamonodominated by CM (ie RDENSCM gt 05) Bold black lines represent significative (Pgt 0005) linear relationships between species richness and theposition along the transects across the CM population

318 Australian Journal of Botany T Ibanez and P Birnbaum

CM within a matrix of mixed tropical rainforest (SAMPLE-1)is likely to result from the margin expansion of CM forestfrom mixed forest edges toward savanna (SAMPLE-2) Thepresence of remnant MQ savanna trees a shade-intolerantspecies (Serbesoff-King 2003) in the CM tree populationsindicates that this species occurred in the savannas before theestablishment of CM (Ibanez et al 2013c) This hypothesis issupported by the presence of seedlings and small trees of CMin savannas (SAMPLE-2)

The recruitment pool under CM canopy was stronglydominated by mixed forest species which suggests thatmonodominance will not persist one more generation in theabsence of disturbance (Connell and Lowman 1989 Hart1990) Although CM small trees and seedlings were veryscarce in SAMPLE-1 they were substantially more abundantin places where light availability was higher as in tree gaps(SAMPLE-1 T Ibanez pers obs) or near the forest edge(SAMPLE-2) This is consistent with prolific seedlinggermination of shade-intolerant species following canopyopening (eg by tree fall or defoliation) (Marimon et al 2012Read and Jaffre 2013) Nevertheless as shown by Newberyet al (2013) the openness created by the fall of a single treemay be insufficient to allow the recruitment in the canopy level

The spatial pattern of species richness and the analysis ofspecies composition suggest that mixed rainforest will succeedto CM population by margin expansion At middle elevationsthe landscape of New Caledonia mainly consists of a mosaic ofsavannas (or maquis on ultramafic substrates) maintained bybush fires and remnant rainforest patches in valleys and gullies(ie valley path see Jaffreacute et al 1998a Ibanez et al 2013a)In contrast to New Caledonian Nothofagus which establishesin mixed forest areas after severe disturbance (Read and Jaffre2013) our results showed that CM can establish in opensavanna and thus initiate forest recovery The pattern of CMdominance and species richness in SAMPLE-1 suggests that theestablishment of CM and the subsequent enrichment of mixedforest species begin at the edge of forest located along valleysand gullies and then progressively extends toward the crest

(see also Ibanez et al 2013a) The formation of belt of CMalong forest edges (SAMPLE-2) is likely to be due to mostfavourable conditions for the establishment of CM trees thereIndeed relativelywet conditions in the savanna close to the forestedge may promote forest expansion by limiting fire spread(Ibanez et al 2012)

Drivers of C mackeeana dominance

Monodominance during early stages of succession is widelyattributed to the massive establishment of a single highlyvagile and rapidly growing species (Hart 1990) The small sizerange of CM in locations where it was dominant suggests thatits dominance results from massive establishment of a singlecohort Codia may fit to this model as it produces indehiscentfruits with many woolly wind-dispersed seeds (Hopkins 2005)However many others species located in the study area(including other Cunoniaceae) possess these traits but do notproduce monodominant forests (see Ibanez 2012) Peh et al(2011) stated that poor seed dispersal leading to gregarioushabit is one mechanism that favours monodominance

The main plant attributes acting on dispersal pattern ofwind-dispersed seeds are the aerodynamic properties ofdiaspores and the height from which they are released (Greeneand Johnson 1989 Nathan et al 2001 Muller-Landau et al2008) Although wind-dispersed seeds may be dispersed faraway most seeds are dispersed close to the parent treeespecially if it is not tall Field observations showed thatCodia is likely to be fertile very early in its ontogeny and thusrapidly disperses seeds from a low height (lt5m) after itsestablishment in an open area This leads to the formation ofdense thickets of CM shrubs which may exclude theestablishment of other species and promote the developmentof CM monodominant forest

Monodominance is also promoted by competitive advantages(Peh et al 2011) such as adaptation to the frequent fire andpoor-nutrient soils of this study system Codia species have acombination of traits that allow them to tolerate fire For

Table 1 Number of trees (diameter at breat height (DBH)$10 cm) and small trees (5 DBHlt 10 cm) of the15 most common species in the three compartments of transects savanna (S) Codia mackeeana population (C) and

mixed rainforest (F)

Species Family Trees Small treesS C F S C F

Codia mackeeana Cunoniaceae 4 125 ndash 5 49 2Melaleuca quinquenervia Myrtaceae 47 12 ndash 104 15 ndash

Myodocarpus sp Myodocarpaceae 2 13 ndash 10 27 1Garcinia virgata Clusiaceae ndash 9 6 ndash 13 2Plerandra pancheri Araliaceae ndash 13 7 ndash 4 1Calophyllum caledonicum Calophyllaceae ndash 7 14 ndash ndash ndash

Myodocarpus pinnatus Myodocarpaceae ndash 11 2 2 3 ndash

Myrsine arborea Primulaceae ndash 4 5 ndash ndash 4Storthocalyx sp Sapindaceae ndash ndash 8 ndash 3 2Styphelia cf cymbulae Ericaceae ndash 2 ndash ndash 3 5Diospyros olen Ebenaceae ndash ndash 1 ndash 2 4Guioa glauca Sapindaceae ndash ndash 2 ndash 4 ndash

Weinmannia serrata Cunoniaceae ndash 4 ndash 2 ndash

Podocarpus sylvestris Podocarpaceae ndash 2 2 ndash ndash 2Denhamia fournieri subsp Drakeana Celastraceae ndash 1 4 ndash ndash ndash

Monodominance at the rainforest edge Australian Journal of Botany 319

exampleC albicans has relatively thick bark and its investmentin bark thickness is disproportionally higher when the trees aresmall (Ibanez et al 2013b) enhancing its probability ofestablishment in fire-prone ecosystems (see Jackson et al1999 Lawes et al 2013) Furthermore all Codia species arelikely to be able to resprout after fire enhancing the probabilityof persistence in fire-prone ecosystems (Gignoux et al 1997Higgins et al 2000) Resprouting has been observed forC discolour and C nitida in maquis (Jaffre et al 1998b) andfor C albicans and C montana in savannas (Ibanez 2012) CMis also possibly pre-adapted to poor-nutrient soils giving it acompetitive advantage (Pillon et al 2009)

Conclusions

The monodominance of CM is clearly an early and non-persistent step in the secondary succession from savanna tomixed rainforest Given our state of knowledge it is difficult toidentify which combination of traits and environmental conditionslead to the monodominance of CM Monodominance in earlysuccession often results from a disturbance such as fire and thepresence of a species well adapted to and able to rapidly occupythe disturbed environment It is crucial to understand suchvegetation dynamics in order to effectively manage these areasHere rather than preventing recovery CM likely allowed aquick closure of anthropogenic savannas followed by a slowrecovery of diversity toward a mixed rainforest Moststudies have focussed on the ecosystem lsquoconsequencesrsquo ofmonodominant forest (eg Torti et al 2001 Brookshire andThomas 2013) but species such as CM that are able to rapidlyoccupy a disturbed environment and even form monodominantforest may provide ecosystem lsquobenefitsrsquo for example by limitingsoil erosion and maintaining soil quality

Acknowledgements

This work was funded by the Southern Province of New Caledonia(C 315-12) We thank the personnel of the provincial park Parc desGrands Fougegraveres for their hospitality and logistical support as well as thestaff of Noumeacutearsquos herbarium of IRD We are grateful to Juliane KaohGendrilla Warimavute Paul Birmbaum and Michegravele Magat for help withfieldwork andCeacutelineChambreyVanessaHequet andHerveacuteVandrot for plantidentification We thank Jennifer Read Tanguy Jaffreacute Lynda Prior as well astwo anonymous reviewers for their valuable comments on the manuscript

References

Brookshire ENJ Thomas SA (2013) Ecosystem consequences of treemonodominance for nitrogen cycling in lowland tropical forest PLoSONE 8 1ndash7

Chatain A Read J Jaffre T (2009) Does leaf-level nutrient-use efficiencyexplain Nothofagus-dominance of some tropical rain forests in NewCaledonia Plant Ecology 201 51ndash66 doi101007s11258-008-9477-z

Connell JH Lowman MD (1989) Low-diversity tropical rain forests ndash somepossible mechanisms for their existence American Naturalist 13488ndash119 doi101086284967

DegagneRSHenkel TW Steinberg SJ Fox Iii L (2009) IdentifyingDicymbecorymbosa monodominant forests in Guyana using satellite imageryBiotropica 41 7ndash15 doi101111j1744-7429200800446x

Fonty E Molino J-F Prevost M-F Sabatier D (2011) A new case ofneotropical monodominant forest Spirotropis longifolia

(LeguminosaendashPapilionoideae) in French Guiana Journal of TropicalEcology 27 641ndash644 doi101017S0266467411000356

Gignoux J Clobert J Menaut JC (1997) Alternative fire resistancestrategies in savanna trees Oecologia 110 576ndash583doi101007s004420050198

Greene DF Johnson EA (1989) A model of wind dispersal of winged orplumed seeds Ecology 70 339ndash347 doi1023071937538

Hart TB (1990) Monospecific dominance in tropical rain forests Trends inEcology amp Evolution 5 6ndash11 doi1010160169-5347(90)90005-X

Hart TB Hart JA Murphy PG (1989) Monodominant and species-richforests of the humid tropics causes for their co-occurrence AmericanNaturalist 133 613ndash633 doi101086284941

Henkel TW (2003) Monodominance in the ectomycorrhizal Dicymbecorymbosa (Caesalpiniaceae) from Guyana Journal of TropicalEcology 19 417ndash437 doi101017S0266467403003468

Higgins SI Bond WJ Trollope WSW (2000) Fire resprouting andvariability a recipe for grass-tree coexistence in savanna Journal ofEcology 88 213ndash229 doi101046j1365-2745200000435x

Hopkins HCF (2005) Nomenclature and typification in the endemic genusCodia (Cunoniaceae) from New Caledonia Adansonia 27 243ndash254

Hopkins HCF Fogliani B Pillon Y (2007) Four new species in the endemicgenus Codia (Cunoniaceae) from New Caledonia Kew Bulletin 62259ndash274

Ibanez T (2012) lsquoDynamique des forecircts denses humides et des savanes enreacuteponse aux incendies en Nouvelle-Caleacutedoniersquo Rainforest and savannadynamics in response to fires in New Caledonia (Universiteacute Aix-Marseille Aix en Provence France)

Ibanez T Heacutely C Curt T Gaucherel C (2012) Sharp transitions ofmicroclimatic conditions between savanna and forest in NewCaledonia insights into vulnerability of forest edges to fire AustralEcology doi101111aec12015

Ibanez T Borgniet L Mangeas M Gaucherel C Geacuteraux H Heacutely C (2013a)Rainforest and savanna landscape dynamics in New Caledonia towardsa mosaic of stable rainforest and savanna states Austral Ecology 3833ndash45 doi101111j1442-9993201202369x

Ibanez T Curt T Heacutely C (2013b) Low tolerance of New Caledoniansecondary forest species to savanna fires Journal of VegetationScience 24 177ndash188 doi101111j1654-1103201201448x

Ibanez TMunzinger J Dagostini G Hequet V Rigault F Jaffreacute T BirnbaumP (2014) Structural and floristic diversity of mixed tropical rain forest inNew Caledonia new data from the New Caledonian Plant Inventoryand Permanent Plot Network (NC-PIPPN) Applied Vegetation Science17 386ndash397

Ibanez T Munzinger J Gaucherel C Curt T Heacutely C (2013c) Inferringsavannah-rainforest boundary dynamics from vegetation structure andcomposition a case study in New Caledonia Australian Journal ofBotany 61 128ndash138 doi101071BT12255

Jackson JF Adams DC Jackson UB (1999) Allometry of constitutivedefense a model and a comparative test with tree bark and fire regimeAmerican Naturalist 153 614ndash632 doi101086303201

Jaffreacute T Bouchet P Veillon JM (1998a) Threatened plants of NewCaledonia is the system of protected areas adequate Biodiversity andConservation 7 109ndash135 doi101023A1008815930865

Jaffre T Rigault F Dagostini G (1998b) Impact des feux de brousse surles maquis ligno-herbaceacutes des roches ultramafiques de Nouvelle-Caleacutedonie Adansonia 20 173ndash189

Lawes MJ Midgley JJ Clarke PJ (2013) Costs and benefits of relative barkthickness in relation to fire damage a savannaforest contrast Journalof Ecology 101 517ndash524 doi1011111365-274512035

Marimon BS Felfili JM Fagg CW Marimon-Junior BH Umetsu RKOliveira-Santos C Morandi PS Lima HS Terra Nascimento AR(2012) Monodominance in a forest of Brosimum rubescens Taub(Moraceae) structure and dynamics of natural regeneration ActaOecologica 43 134ndash139 doi101016jactao201207001

320 Australian Journal of Botany T Ibanez and P Birnbaum

structures recruitment pools (amount of small trees andseedlings) and species richness using linear relationships Inthe absence of growth-rate data we inferred the age of thepopulations using the distribution of DBH to study thedynamics of CM Although growth rates may differ accordingto the environment (eg savanna vs forest) we assumed thatthe distribution of the DBH is positively correlated with the ageof the individuals hence older CM populations should exhibitlarger DBH Species community patterns in SAMPLE-1 werecomputed using non-metric multi-dimensional scaling (NMDS)using the R package vegan (Oksanen et al 2012) All statisticsanalysis was performed using the R 2152 environment forstatistical computing (R Core Team 2012)

Results

Dominance of the canopy by C mackeeana

Across all samples almost 40 of the 2004 inventoried canopy-level trees (DBH 10 cm encompassing trees ferns and palms)belonged to C mackeeana (CM) In SAMPLE-1 when CMwas

present (32 over 37 points) its relative density (RDENSCM)ranged from 002 to 097 (044 030 sd in average) andRDENSCM was 05 (ie CM monodominance) in 14 of 32points (Fig 2) Considering the biomass the dominance ofCM was even more important with RBACM ranging from 004to 099 (060 030 sd in average) and RBACM05 in 20sampling points

No other species exhibits monodominance The secondmost abundant tree species was the savanna remnant treeM quinquenervia (MQ) Live MQ occurred in 12 samplingpoints (18 taking into account dead trees) mainly located alongthe ridges and showed low relative densities (RDENSMQ

ranged from 002 to 029) and basal area (RBAMQ rangedfrom 001 to 057) The maximum RDENS and RBA valuesobserved from all other forest species never exceeded 05 andranged from 001 to 049 (015 009 sd in average) and from001 to 041 (014 011 sd in average) respectively

The CM populations occupied 20ndash60m (ie 200ndash600m2) ofthe five studied transects (SAMPLE-2) RDENSCM ranged from043 to 068 (053 009 sd in average) and RBACM ranged

Longitude (DD)

Latit

ude

(DD

)

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

Codia mackeeana Melaleuca quinquenervia Max(other species)

Relative density

Relative basal area

1657635 1657645 1657655 1657635 1657645 1657655 1657635 1657645 1657655

Value 0 025 050 100times

(a) (b) (c)

(d) (e) (f)

430 430 430

430 430

450 450

460 460

470 470

430 430

430 430

440 440

440 440

430 430

430 430

420

420

440 440

450 450

460 460

470 470

440

440

440 440420

420

440 440

440 440

430

440

440450

460

70

430

430

440

440450

460

430

440420

430 440

440

440

440

440420

Fig 2 Spatial variation in (andashc) relative density and (endashf) relative basal area of Codia mackeeana Melaleuca quinquenervia and maximum values for allother species pooled together Point size is proportional to values of relative density or relative dominanceBlackpoints indicate valuesgt05 (iemonodominance)and crosses null values Contour lines represent elevation isoclines (10m)

Monodominance at the rainforest edge Australian Journal of Botany 315

from 052 to 067 (060 008 sd in average) Moving windowanalysis highlighted heterogeneity in these populations(Fig 3andashe) RDENSCM ranged from 02 to 1 and the areasidentified as monodominated by CM (ie RDENSCM 05)were smaller (37ndash81 of the area) The transition fromsavanna to the CM population was very sharp whereas thetransition from CM populations to mixed forest was moregradual

In both samples the dominance of CM mainly reflected ahigh density of small stems In sampling points dominated byCM (SAMPLE-1) the median DBH of CM was 197 cm (range

100ndash643 cm) while in other sampling points the median DBHwas 299 cm (10ndash914 cm) (Fig 4) A similar pattern wasobserved along transects (SAMPLE-2) with a high density ofCM small stems (Fig 5) Most (nearly 75) CM trees wereinventoried in the first 20m behind the savannandashforest edge withmedian DBH of 141 cm Overall the median DBH increasedlinearly with the distance from the savannandashforest edge

Scarce recruitment of C mackeeana in the undergrowth

In total 53 small trees (ie 5 cmDBH lt 10 cm) and 1382seedlings (ie height50 cm and DBH lt 5 cm) were

Transect 1 Transect 2 Transect 3

Transect 4 Transect 5

Position along the transect (m)

Position along the transect (m)

Rel

ativ

e de

nsity

Rel

ativ

e de

nsity

TreesS

mall trees

Seedlings

TreesS

mall trees

Seedlings

OtherCMMQ

OtherCMMQ

For

est

Savannah

OtherMQ

CM

(a) (b) (c)

(f ) (g) (h)

(k) (l ) (m )

(d )

(i )

(n ) (o )

(j )

(e )

Fig 3 Relative density profiles (andashe) of canopy-level trees (diameter at breast height (DBH) 10 cm) and (fndashj) undergrowth-level small trees(5 cmDBH lt 10 cm) Lines represent smoothing values of relative densities of Codia makeeana (CM full black lines) Melaleuca quinquenervia (MQfull grey lines) and other species (Other dotted black lines) Grey areas highlight areas where CM is considered as monodominant (RDENSCM gt 05) Bottomgraphs (kndasho) represent the locations of CM MQ and other species seedlings (50-cm height and DBH of lt5 cm) along the transects

316 Australian Journal of Botany T Ibanez and P Birnbaum

inventoried in the undergrowth of SAMPLE-1 This regenerationpool was by far dominated by forest species (94 of the smalltrees and 99 of the seedlings) Regeneration of CM was scarce(3 small trees and 19 seedlings located in only 3 and 7 of the 37sample points respectively) and neither MQ small trees norseedlings were observed in the undergrowth No clearrelationships between the characteristics of the CM canopy-level population and regeneration pool were detected

In contrast in SAMPLE-2 many CM small trees wererecorded in the undergrowth of the CM canopy-levelpopulation (Fig 3fndashj) Nevertheless compared with thecanopy-level population the extent and the relative dominancein the undergrowth decreased as the dominance of other forestspecies increased Only 10 of the 393 inventoried seedlingswere CM (81 were forest species and 9 were MQ) CMseedlings were found both under CM canopy and in opensavanna (up to 172m in front of the forest edge) at similardensities (015 seedlings mndash2 on average Wilcoxon testP-value gt005) Conversely MQ seedlings were found only insavannas (Fig 3kndasho) Seedlings of forest species occurredall along transects and their number increased significantly(chi-square test P-value lt0001) from savanna to mixed forest

(8 in savanna 36 in the CM population and 56 in themixed forest)

Species richness and species composition patterns

Despite the dominance of CM 121 taxa belonging to 50families were identified (24 trees were not identified seeAppendix S1 available as Supplementary Material for thispaper) In SAMPLE-1 canopy-level species richness wasnegatively correlated with RDENSCM (Fig 6a b) In samplingpoints where CM occurred species richness ranged from 3 fora RDENSCM of 094 to 23 for a RDENSCM of 004 whereasspecies richness reached up to 30 in adjacent mixed forestOverall the spatial pattern of species richness in SAMPLE-1suggested that species richness increased from CM populationslocated on the ridges and upslope to mixed rainforest locateddownslope This pattern was highlighted in the SAMPLE-2with species richness increasing from savanna located upslopeor on the ridges to mixed forest located downslope (Fig 7) Theprofiles of species richness and cumulative number of specieswere not affected by the CM population

Interpreting floristic composition was difficult because ofthe overall rarity of species in both samplings Only 31 specieswere represented by more than 10 trees and only 23 of themwere inventoried in both samplings In SAMPLE-1 NMDShighlighted gradual changes rather than clearly distinct plantcomposition Distribution of the most common species alongtransects (Table 1) suggested that no species were able to growin all three compartments of our transects However mostspecies occurred either in savannandashCM interface or theCM-mixed forest one As a result the canopy between the

(a) (b)10

06

04

02

0

RD

EN

SC

M250

200

150

100

50

0Fr

eque

ncy

10 20 30 40 50 60 70 80

DBHCM

08

20 40 60DBHCM

80 100

Fig 4 Populations size structure of Codia mackeeana trees (CM) inSAMPLE-1 (a) Diameter at breast height of CM (DBHCM) as a functionof the relative density of CM (RDENSCM) points represent the median valueand bars the 1st and 3rd quartiles intervals (the grey tone of the points isproportional to RDENSCM) Median values were significantly smaller whenRDENSCM05 (Wilcoxon rank sums test Plt 0001) (b) Histogram ofthe distribution of DBHCM all sampling points for which RDENSCM05pooled together

20

60

50

40

30

20

10

40

Position along the transect (m)

DB

HC

M

60 80

T1T2T3T4

T5

Fig 5 Size distribution of Codia mackeeana (DBHCM) according tothe position of the trees along the transects (Pearsonrsquos r= 034 P-valuelt0001) Dark solid line represents linear quantile regression for q= 05(median y= 020x+ 847) and grey polygon represents the intervalbetween the linear quantile regressions for q= 025 and q= 075 Thevertical black line represents the forestndashsavanna edge

Monodominance at the rainforest edge Australian Journal of Botany 317

savanna and the mixed forest although dominated by CMconsisted of a mixture of pioneer species such Myodocarpusspecies (mostly found close to the savanna) as well as foresttree species such as Garcinia virgata Plerandra pancheri orCalophyllum caledonicum (mostly found close to the mixedforest) Additional small trees such as Guioa glauca orDiospyros olen enriched the undergrowth

Discussion

Monodominance of C mackeeanea a step in thesuccessional process

Our results suggest that the observed CM populations constitutean early and non-persistent step in the process of successionfrom savanna to mixed tropical rainforest The studied patch of

1657635

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

1657645

Longitude (DD) 1-RDENSCM NDMS11657655 00 02 04 06 08 10 ndash04 ndash02 00 02 04

Latit

ude

(DD

)

R2 = 072lowastlowastlowast FOR

20

15

10

5

Spe

cies

ric

hnes

s

04

02

00

ndash02

ndash04

ND

MS

2

(c)(b)

y = 41 + 148

lowast x

MQ

CM

Stress = 015(a)

430

440450

460

470

430

440420

440

Fig 6 Distribution of species richness and relationship with relative density ofCodia mackeeana (RDENSCM) in the SAMPLE-1 point size is proportional tospecies richness and point colour is proportional to RDENSCM (linear grey scales white for RDENSCM= 0 and black for RDENSCM= 1 (a) Map of samplingpoints contour lines represent elevation isoclines (10m) (b) Linear relationship between species richness andRDENSCM (sampling points where RDENSCM= 0were removed) (c) Ordination of sampling points using non-metric multidimensional scaling (non-metric multidimensional scaling 2D-solution) CMindicates points where RDENSCM05 MQ points where alive Melaleuca quiquenervia were inventoried but no C mackeeanea and FOR mixed forestpoints where neither C mackeeanea nor M quinquenervia were inventoried

Transect 1

Transect 4 Transect 5

Transect 2 Transect 3

0 10 20 30 40 50 60

0 20 40 60 80 100

Position along the transect (m)

0 10 20 30 40 50 60

0 10 20 30 40 50 60 0 10 20 30 40 5070

40

30

20

10

0

40

30

20

10

0

Spe

cies

ric

hnes

s amp

cum

ulat

ive

num

ber

of s

peci

es

Fig 7 Smoothed local species richness (black lines) and cumulative number of species (dotted lines) along the five studied transects (trees and small treespooled together) Vertical black lines represent first and last inventoried Codia mackeeana (CM) along the transects and grey areas represent areamonodominated by CM (ie RDENSCM gt 05) Bold black lines represent significative (Pgt 0005) linear relationships between species richness and theposition along the transects across the CM population

318 Australian Journal of Botany T Ibanez and P Birnbaum

CM within a matrix of mixed tropical rainforest (SAMPLE-1)is likely to result from the margin expansion of CM forestfrom mixed forest edges toward savanna (SAMPLE-2) Thepresence of remnant MQ savanna trees a shade-intolerantspecies (Serbesoff-King 2003) in the CM tree populationsindicates that this species occurred in the savannas before theestablishment of CM (Ibanez et al 2013c) This hypothesis issupported by the presence of seedlings and small trees of CMin savannas (SAMPLE-2)

The recruitment pool under CM canopy was stronglydominated by mixed forest species which suggests thatmonodominance will not persist one more generation in theabsence of disturbance (Connell and Lowman 1989 Hart1990) Although CM small trees and seedlings were veryscarce in SAMPLE-1 they were substantially more abundantin places where light availability was higher as in tree gaps(SAMPLE-1 T Ibanez pers obs) or near the forest edge(SAMPLE-2) This is consistent with prolific seedlinggermination of shade-intolerant species following canopyopening (eg by tree fall or defoliation) (Marimon et al 2012Read and Jaffre 2013) Nevertheless as shown by Newberyet al (2013) the openness created by the fall of a single treemay be insufficient to allow the recruitment in the canopy level

The spatial pattern of species richness and the analysis ofspecies composition suggest that mixed rainforest will succeedto CM population by margin expansion At middle elevationsthe landscape of New Caledonia mainly consists of a mosaic ofsavannas (or maquis on ultramafic substrates) maintained bybush fires and remnant rainforest patches in valleys and gullies(ie valley path see Jaffreacute et al 1998a Ibanez et al 2013a)In contrast to New Caledonian Nothofagus which establishesin mixed forest areas after severe disturbance (Read and Jaffre2013) our results showed that CM can establish in opensavanna and thus initiate forest recovery The pattern of CMdominance and species richness in SAMPLE-1 suggests that theestablishment of CM and the subsequent enrichment of mixedforest species begin at the edge of forest located along valleysand gullies and then progressively extends toward the crest

(see also Ibanez et al 2013a) The formation of belt of CMalong forest edges (SAMPLE-2) is likely to be due to mostfavourable conditions for the establishment of CM trees thereIndeed relativelywet conditions in the savanna close to the forestedge may promote forest expansion by limiting fire spread(Ibanez et al 2012)

Drivers of C mackeeana dominance

Monodominance during early stages of succession is widelyattributed to the massive establishment of a single highlyvagile and rapidly growing species (Hart 1990) The small sizerange of CM in locations where it was dominant suggests thatits dominance results from massive establishment of a singlecohort Codia may fit to this model as it produces indehiscentfruits with many woolly wind-dispersed seeds (Hopkins 2005)However many others species located in the study area(including other Cunoniaceae) possess these traits but do notproduce monodominant forests (see Ibanez 2012) Peh et al(2011) stated that poor seed dispersal leading to gregarioushabit is one mechanism that favours monodominance

The main plant attributes acting on dispersal pattern ofwind-dispersed seeds are the aerodynamic properties ofdiaspores and the height from which they are released (Greeneand Johnson 1989 Nathan et al 2001 Muller-Landau et al2008) Although wind-dispersed seeds may be dispersed faraway most seeds are dispersed close to the parent treeespecially if it is not tall Field observations showed thatCodia is likely to be fertile very early in its ontogeny and thusrapidly disperses seeds from a low height (lt5m) after itsestablishment in an open area This leads to the formation ofdense thickets of CM shrubs which may exclude theestablishment of other species and promote the developmentof CM monodominant forest

Monodominance is also promoted by competitive advantages(Peh et al 2011) such as adaptation to the frequent fire andpoor-nutrient soils of this study system Codia species have acombination of traits that allow them to tolerate fire For

Table 1 Number of trees (diameter at breat height (DBH)$10 cm) and small trees (5 DBHlt 10 cm) of the15 most common species in the three compartments of transects savanna (S) Codia mackeeana population (C) and

mixed rainforest (F)

Species Family Trees Small treesS C F S C F

Codia mackeeana Cunoniaceae 4 125 ndash 5 49 2Melaleuca quinquenervia Myrtaceae 47 12 ndash 104 15 ndash

Myodocarpus sp Myodocarpaceae 2 13 ndash 10 27 1Garcinia virgata Clusiaceae ndash 9 6 ndash 13 2Plerandra pancheri Araliaceae ndash 13 7 ndash 4 1Calophyllum caledonicum Calophyllaceae ndash 7 14 ndash ndash ndash

Myodocarpus pinnatus Myodocarpaceae ndash 11 2 2 3 ndash

Myrsine arborea Primulaceae ndash 4 5 ndash ndash 4Storthocalyx sp Sapindaceae ndash ndash 8 ndash 3 2Styphelia cf cymbulae Ericaceae ndash 2 ndash ndash 3 5Diospyros olen Ebenaceae ndash ndash 1 ndash 2 4Guioa glauca Sapindaceae ndash ndash 2 ndash 4 ndash

Weinmannia serrata Cunoniaceae ndash 4 ndash 2 ndash

Podocarpus sylvestris Podocarpaceae ndash 2 2 ndash ndash 2Denhamia fournieri subsp Drakeana Celastraceae ndash 1 4 ndash ndash ndash

Monodominance at the rainforest edge Australian Journal of Botany 319

exampleC albicans has relatively thick bark and its investmentin bark thickness is disproportionally higher when the trees aresmall (Ibanez et al 2013b) enhancing its probability ofestablishment in fire-prone ecosystems (see Jackson et al1999 Lawes et al 2013) Furthermore all Codia species arelikely to be able to resprout after fire enhancing the probabilityof persistence in fire-prone ecosystems (Gignoux et al 1997Higgins et al 2000) Resprouting has been observed forC discolour and C nitida in maquis (Jaffre et al 1998b) andfor C albicans and C montana in savannas (Ibanez 2012) CMis also possibly pre-adapted to poor-nutrient soils giving it acompetitive advantage (Pillon et al 2009)

Conclusions

The monodominance of CM is clearly an early and non-persistent step in the secondary succession from savanna tomixed rainforest Given our state of knowledge it is difficult toidentify which combination of traits and environmental conditionslead to the monodominance of CM Monodominance in earlysuccession often results from a disturbance such as fire and thepresence of a species well adapted to and able to rapidly occupythe disturbed environment It is crucial to understand suchvegetation dynamics in order to effectively manage these areasHere rather than preventing recovery CM likely allowed aquick closure of anthropogenic savannas followed by a slowrecovery of diversity toward a mixed rainforest Moststudies have focussed on the ecosystem lsquoconsequencesrsquo ofmonodominant forest (eg Torti et al 2001 Brookshire andThomas 2013) but species such as CM that are able to rapidlyoccupy a disturbed environment and even form monodominantforest may provide ecosystem lsquobenefitsrsquo for example by limitingsoil erosion and maintaining soil quality

Acknowledgements

This work was funded by the Southern Province of New Caledonia(C 315-12) We thank the personnel of the provincial park Parc desGrands Fougegraveres for their hospitality and logistical support as well as thestaff of Noumeacutearsquos herbarium of IRD We are grateful to Juliane KaohGendrilla Warimavute Paul Birmbaum and Michegravele Magat for help withfieldwork andCeacutelineChambreyVanessaHequet andHerveacuteVandrot for plantidentification We thank Jennifer Read Tanguy Jaffreacute Lynda Prior as well astwo anonymous reviewers for their valuable comments on the manuscript

References

Brookshire ENJ Thomas SA (2013) Ecosystem consequences of treemonodominance for nitrogen cycling in lowland tropical forest PLoSONE 8 1ndash7

Chatain A Read J Jaffre T (2009) Does leaf-level nutrient-use efficiencyexplain Nothofagus-dominance of some tropical rain forests in NewCaledonia Plant Ecology 201 51ndash66 doi101007s11258-008-9477-z

Connell JH Lowman MD (1989) Low-diversity tropical rain forests ndash somepossible mechanisms for their existence American Naturalist 13488ndash119 doi101086284967

DegagneRSHenkel TW Steinberg SJ Fox Iii L (2009) IdentifyingDicymbecorymbosa monodominant forests in Guyana using satellite imageryBiotropica 41 7ndash15 doi101111j1744-7429200800446x

Fonty E Molino J-F Prevost M-F Sabatier D (2011) A new case ofneotropical monodominant forest Spirotropis longifolia

(LeguminosaendashPapilionoideae) in French Guiana Journal of TropicalEcology 27 641ndash644 doi101017S0266467411000356

Gignoux J Clobert J Menaut JC (1997) Alternative fire resistancestrategies in savanna trees Oecologia 110 576ndash583doi101007s004420050198

Greene DF Johnson EA (1989) A model of wind dispersal of winged orplumed seeds Ecology 70 339ndash347 doi1023071937538

Hart TB (1990) Monospecific dominance in tropical rain forests Trends inEcology amp Evolution 5 6ndash11 doi1010160169-5347(90)90005-X

Hart TB Hart JA Murphy PG (1989) Monodominant and species-richforests of the humid tropics causes for their co-occurrence AmericanNaturalist 133 613ndash633 doi101086284941

Henkel TW (2003) Monodominance in the ectomycorrhizal Dicymbecorymbosa (Caesalpiniaceae) from Guyana Journal of TropicalEcology 19 417ndash437 doi101017S0266467403003468

Higgins SI Bond WJ Trollope WSW (2000) Fire resprouting andvariability a recipe for grass-tree coexistence in savanna Journal ofEcology 88 213ndash229 doi101046j1365-2745200000435x

Hopkins HCF (2005) Nomenclature and typification in the endemic genusCodia (Cunoniaceae) from New Caledonia Adansonia 27 243ndash254

Hopkins HCF Fogliani B Pillon Y (2007) Four new species in the endemicgenus Codia (Cunoniaceae) from New Caledonia Kew Bulletin 62259ndash274

Ibanez T (2012) lsquoDynamique des forecircts denses humides et des savanes enreacuteponse aux incendies en Nouvelle-Caleacutedoniersquo Rainforest and savannadynamics in response to fires in New Caledonia (Universiteacute Aix-Marseille Aix en Provence France)

Ibanez T Heacutely C Curt T Gaucherel C (2012) Sharp transitions ofmicroclimatic conditions between savanna and forest in NewCaledonia insights into vulnerability of forest edges to fire AustralEcology doi101111aec12015

Ibanez T Borgniet L Mangeas M Gaucherel C Geacuteraux H Heacutely C (2013a)Rainforest and savanna landscape dynamics in New Caledonia towardsa mosaic of stable rainforest and savanna states Austral Ecology 3833ndash45 doi101111j1442-9993201202369x

Ibanez T Curt T Heacutely C (2013b) Low tolerance of New Caledoniansecondary forest species to savanna fires Journal of VegetationScience 24 177ndash188 doi101111j1654-1103201201448x

Ibanez TMunzinger J Dagostini G Hequet V Rigault F Jaffreacute T BirnbaumP (2014) Structural and floristic diversity of mixed tropical rain forest inNew Caledonia new data from the New Caledonian Plant Inventoryand Permanent Plot Network (NC-PIPPN) Applied Vegetation Science17 386ndash397

Ibanez T Munzinger J Gaucherel C Curt T Heacutely C (2013c) Inferringsavannah-rainforest boundary dynamics from vegetation structure andcomposition a case study in New Caledonia Australian Journal ofBotany 61 128ndash138 doi101071BT12255

Jackson JF Adams DC Jackson UB (1999) Allometry of constitutivedefense a model and a comparative test with tree bark and fire regimeAmerican Naturalist 153 614ndash632 doi101086303201

Jaffreacute T Bouchet P Veillon JM (1998a) Threatened plants of NewCaledonia is the system of protected areas adequate Biodiversity andConservation 7 109ndash135 doi101023A1008815930865

Jaffre T Rigault F Dagostini G (1998b) Impact des feux de brousse surles maquis ligno-herbaceacutes des roches ultramafiques de Nouvelle-Caleacutedonie Adansonia 20 173ndash189

Lawes MJ Midgley JJ Clarke PJ (2013) Costs and benefits of relative barkthickness in relation to fire damage a savannaforest contrast Journalof Ecology 101 517ndash524 doi1011111365-274512035

Marimon BS Felfili JM Fagg CW Marimon-Junior BH Umetsu RKOliveira-Santos C Morandi PS Lima HS Terra Nascimento AR(2012) Monodominance in a forest of Brosimum rubescens Taub(Moraceae) structure and dynamics of natural regeneration ActaOecologica 43 134ndash139 doi101016jactao201207001

320 Australian Journal of Botany T Ibanez and P Birnbaum

from 052 to 067 (060 008 sd in average) Moving windowanalysis highlighted heterogeneity in these populations(Fig 3andashe) RDENSCM ranged from 02 to 1 and the areasidentified as monodominated by CM (ie RDENSCM 05)were smaller (37ndash81 of the area) The transition fromsavanna to the CM population was very sharp whereas thetransition from CM populations to mixed forest was moregradual

In both samples the dominance of CM mainly reflected ahigh density of small stems In sampling points dominated byCM (SAMPLE-1) the median DBH of CM was 197 cm (range

100ndash643 cm) while in other sampling points the median DBHwas 299 cm (10ndash914 cm) (Fig 4) A similar pattern wasobserved along transects (SAMPLE-2) with a high density ofCM small stems (Fig 5) Most (nearly 75) CM trees wereinventoried in the first 20m behind the savannandashforest edge withmedian DBH of 141 cm Overall the median DBH increasedlinearly with the distance from the savannandashforest edge

Scarce recruitment of C mackeeana in the undergrowth

In total 53 small trees (ie 5 cmDBH lt 10 cm) and 1382seedlings (ie height50 cm and DBH lt 5 cm) were

Transect 1 Transect 2 Transect 3

Transect 4 Transect 5

Position along the transect (m)

Position along the transect (m)

Rel

ativ

e de

nsity

Rel

ativ

e de

nsity

TreesS

mall trees

Seedlings

TreesS

mall trees

Seedlings

OtherCMMQ

OtherCMMQ

For

est

Savannah

OtherMQ

CM

(a) (b) (c)

(f ) (g) (h)

(k) (l ) (m )

(d )

(i )

(n ) (o )

(j )

(e )

Fig 3 Relative density profiles (andashe) of canopy-level trees (diameter at breast height (DBH) 10 cm) and (fndashj) undergrowth-level small trees(5 cmDBH lt 10 cm) Lines represent smoothing values of relative densities of Codia makeeana (CM full black lines) Melaleuca quinquenervia (MQfull grey lines) and other species (Other dotted black lines) Grey areas highlight areas where CM is considered as monodominant (RDENSCM gt 05) Bottomgraphs (kndasho) represent the locations of CM MQ and other species seedlings (50-cm height and DBH of lt5 cm) along the transects

316 Australian Journal of Botany T Ibanez and P Birnbaum

inventoried in the undergrowth of SAMPLE-1 This regenerationpool was by far dominated by forest species (94 of the smalltrees and 99 of the seedlings) Regeneration of CM was scarce(3 small trees and 19 seedlings located in only 3 and 7 of the 37sample points respectively) and neither MQ small trees norseedlings were observed in the undergrowth No clearrelationships between the characteristics of the CM canopy-level population and regeneration pool were detected

In contrast in SAMPLE-2 many CM small trees wererecorded in the undergrowth of the CM canopy-levelpopulation (Fig 3fndashj) Nevertheless compared with thecanopy-level population the extent and the relative dominancein the undergrowth decreased as the dominance of other forestspecies increased Only 10 of the 393 inventoried seedlingswere CM (81 were forest species and 9 were MQ) CMseedlings were found both under CM canopy and in opensavanna (up to 172m in front of the forest edge) at similardensities (015 seedlings mndash2 on average Wilcoxon testP-value gt005) Conversely MQ seedlings were found only insavannas (Fig 3kndasho) Seedlings of forest species occurredall along transects and their number increased significantly(chi-square test P-value lt0001) from savanna to mixed forest

(8 in savanna 36 in the CM population and 56 in themixed forest)

Species richness and species composition patterns

Despite the dominance of CM 121 taxa belonging to 50families were identified (24 trees were not identified seeAppendix S1 available as Supplementary Material for thispaper) In SAMPLE-1 canopy-level species richness wasnegatively correlated with RDENSCM (Fig 6a b) In samplingpoints where CM occurred species richness ranged from 3 fora RDENSCM of 094 to 23 for a RDENSCM of 004 whereasspecies richness reached up to 30 in adjacent mixed forestOverall the spatial pattern of species richness in SAMPLE-1suggested that species richness increased from CM populationslocated on the ridges and upslope to mixed rainforest locateddownslope This pattern was highlighted in the SAMPLE-2with species richness increasing from savanna located upslopeor on the ridges to mixed forest located downslope (Fig 7) Theprofiles of species richness and cumulative number of specieswere not affected by the CM population

Interpreting floristic composition was difficult because ofthe overall rarity of species in both samplings Only 31 specieswere represented by more than 10 trees and only 23 of themwere inventoried in both samplings In SAMPLE-1 NMDShighlighted gradual changes rather than clearly distinct plantcomposition Distribution of the most common species alongtransects (Table 1) suggested that no species were able to growin all three compartments of our transects However mostspecies occurred either in savannandashCM interface or theCM-mixed forest one As a result the canopy between the

(a) (b)10

06

04

02

0

RD

EN

SC

M250

200

150

100

50

0Fr

eque

ncy

10 20 30 40 50 60 70 80

DBHCM

08

20 40 60DBHCM

80 100

Fig 4 Populations size structure of Codia mackeeana trees (CM) inSAMPLE-1 (a) Diameter at breast height of CM (DBHCM) as a functionof the relative density of CM (RDENSCM) points represent the median valueand bars the 1st and 3rd quartiles intervals (the grey tone of the points isproportional to RDENSCM) Median values were significantly smaller whenRDENSCM05 (Wilcoxon rank sums test Plt 0001) (b) Histogram ofthe distribution of DBHCM all sampling points for which RDENSCM05pooled together

20

60

50

40

30

20

10

40

Position along the transect (m)

DB

HC

M

60 80

T1T2T3T4

T5

Fig 5 Size distribution of Codia mackeeana (DBHCM) according tothe position of the trees along the transects (Pearsonrsquos r= 034 P-valuelt0001) Dark solid line represents linear quantile regression for q= 05(median y= 020x+ 847) and grey polygon represents the intervalbetween the linear quantile regressions for q= 025 and q= 075 Thevertical black line represents the forestndashsavanna edge

Monodominance at the rainforest edge Australian Journal of Botany 317

savanna and the mixed forest although dominated by CMconsisted of a mixture of pioneer species such Myodocarpusspecies (mostly found close to the savanna) as well as foresttree species such as Garcinia virgata Plerandra pancheri orCalophyllum caledonicum (mostly found close to the mixedforest) Additional small trees such as Guioa glauca orDiospyros olen enriched the undergrowth

Discussion

Monodominance of C mackeeanea a step in thesuccessional process

Our results suggest that the observed CM populations constitutean early and non-persistent step in the process of successionfrom savanna to mixed tropical rainforest The studied patch of

1657635

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

1657645

Longitude (DD) 1-RDENSCM NDMS11657655 00 02 04 06 08 10 ndash04 ndash02 00 02 04

Latit

ude

(DD

)

R2 = 072lowastlowastlowast FOR

20

15

10

5

Spe

cies

ric

hnes

s

04

02

00

ndash02

ndash04

ND

MS

2

(c)(b)

y = 41 + 148

lowast x

MQ

CM

Stress = 015(a)

430

440450

460

470

430

440420

440

Fig 6 Distribution of species richness and relationship with relative density ofCodia mackeeana (RDENSCM) in the SAMPLE-1 point size is proportional tospecies richness and point colour is proportional to RDENSCM (linear grey scales white for RDENSCM= 0 and black for RDENSCM= 1 (a) Map of samplingpoints contour lines represent elevation isoclines (10m) (b) Linear relationship between species richness andRDENSCM (sampling points where RDENSCM= 0were removed) (c) Ordination of sampling points using non-metric multidimensional scaling (non-metric multidimensional scaling 2D-solution) CMindicates points where RDENSCM05 MQ points where alive Melaleuca quiquenervia were inventoried but no C mackeeanea and FOR mixed forestpoints where neither C mackeeanea nor M quinquenervia were inventoried

Transect 1

Transect 4 Transect 5

Transect 2 Transect 3

0 10 20 30 40 50 60

0 20 40 60 80 100

Position along the transect (m)

0 10 20 30 40 50 60

0 10 20 30 40 50 60 0 10 20 30 40 5070

40

30

20

10

0

40

30

20

10

0

Spe

cies

ric

hnes

s amp

cum

ulat

ive

num

ber

of s

peci

es

Fig 7 Smoothed local species richness (black lines) and cumulative number of species (dotted lines) along the five studied transects (trees and small treespooled together) Vertical black lines represent first and last inventoried Codia mackeeana (CM) along the transects and grey areas represent areamonodominated by CM (ie RDENSCM gt 05) Bold black lines represent significative (Pgt 0005) linear relationships between species richness and theposition along the transects across the CM population

318 Australian Journal of Botany T Ibanez and P Birnbaum

CM within a matrix of mixed tropical rainforest (SAMPLE-1)is likely to result from the margin expansion of CM forestfrom mixed forest edges toward savanna (SAMPLE-2) Thepresence of remnant MQ savanna trees a shade-intolerantspecies (Serbesoff-King 2003) in the CM tree populationsindicates that this species occurred in the savannas before theestablishment of CM (Ibanez et al 2013c) This hypothesis issupported by the presence of seedlings and small trees of CMin savannas (SAMPLE-2)

The recruitment pool under CM canopy was stronglydominated by mixed forest species which suggests thatmonodominance will not persist one more generation in theabsence of disturbance (Connell and Lowman 1989 Hart1990) Although CM small trees and seedlings were veryscarce in SAMPLE-1 they were substantially more abundantin places where light availability was higher as in tree gaps(SAMPLE-1 T Ibanez pers obs) or near the forest edge(SAMPLE-2) This is consistent with prolific seedlinggermination of shade-intolerant species following canopyopening (eg by tree fall or defoliation) (Marimon et al 2012Read and Jaffre 2013) Nevertheless as shown by Newberyet al (2013) the openness created by the fall of a single treemay be insufficient to allow the recruitment in the canopy level

The spatial pattern of species richness and the analysis ofspecies composition suggest that mixed rainforest will succeedto CM population by margin expansion At middle elevationsthe landscape of New Caledonia mainly consists of a mosaic ofsavannas (or maquis on ultramafic substrates) maintained bybush fires and remnant rainforest patches in valleys and gullies(ie valley path see Jaffreacute et al 1998a Ibanez et al 2013a)In contrast to New Caledonian Nothofagus which establishesin mixed forest areas after severe disturbance (Read and Jaffre2013) our results showed that CM can establish in opensavanna and thus initiate forest recovery The pattern of CMdominance and species richness in SAMPLE-1 suggests that theestablishment of CM and the subsequent enrichment of mixedforest species begin at the edge of forest located along valleysand gullies and then progressively extends toward the crest

(see also Ibanez et al 2013a) The formation of belt of CMalong forest edges (SAMPLE-2) is likely to be due to mostfavourable conditions for the establishment of CM trees thereIndeed relativelywet conditions in the savanna close to the forestedge may promote forest expansion by limiting fire spread(Ibanez et al 2012)

Drivers of C mackeeana dominance

Monodominance during early stages of succession is widelyattributed to the massive establishment of a single highlyvagile and rapidly growing species (Hart 1990) The small sizerange of CM in locations where it was dominant suggests thatits dominance results from massive establishment of a singlecohort Codia may fit to this model as it produces indehiscentfruits with many woolly wind-dispersed seeds (Hopkins 2005)However many others species located in the study area(including other Cunoniaceae) possess these traits but do notproduce monodominant forests (see Ibanez 2012) Peh et al(2011) stated that poor seed dispersal leading to gregarioushabit is one mechanism that favours monodominance

The main plant attributes acting on dispersal pattern ofwind-dispersed seeds are the aerodynamic properties ofdiaspores and the height from which they are released (Greeneand Johnson 1989 Nathan et al 2001 Muller-Landau et al2008) Although wind-dispersed seeds may be dispersed faraway most seeds are dispersed close to the parent treeespecially if it is not tall Field observations showed thatCodia is likely to be fertile very early in its ontogeny and thusrapidly disperses seeds from a low height (lt5m) after itsestablishment in an open area This leads to the formation ofdense thickets of CM shrubs which may exclude theestablishment of other species and promote the developmentof CM monodominant forest

Monodominance is also promoted by competitive advantages(Peh et al 2011) such as adaptation to the frequent fire andpoor-nutrient soils of this study system Codia species have acombination of traits that allow them to tolerate fire For

Table 1 Number of trees (diameter at breat height (DBH)$10 cm) and small trees (5 DBHlt 10 cm) of the15 most common species in the three compartments of transects savanna (S) Codia mackeeana population (C) and

mixed rainforest (F)

Species Family Trees Small treesS C F S C F

Codia mackeeana Cunoniaceae 4 125 ndash 5 49 2Melaleuca quinquenervia Myrtaceae 47 12 ndash 104 15 ndash

Myodocarpus sp Myodocarpaceae 2 13 ndash 10 27 1Garcinia virgata Clusiaceae ndash 9 6 ndash 13 2Plerandra pancheri Araliaceae ndash 13 7 ndash 4 1Calophyllum caledonicum Calophyllaceae ndash 7 14 ndash ndash ndash

Myodocarpus pinnatus Myodocarpaceae ndash 11 2 2 3 ndash

Myrsine arborea Primulaceae ndash 4 5 ndash ndash 4Storthocalyx sp Sapindaceae ndash ndash 8 ndash 3 2Styphelia cf cymbulae Ericaceae ndash 2 ndash ndash 3 5Diospyros olen Ebenaceae ndash ndash 1 ndash 2 4Guioa glauca Sapindaceae ndash ndash 2 ndash 4 ndash

Weinmannia serrata Cunoniaceae ndash 4 ndash 2 ndash

Podocarpus sylvestris Podocarpaceae ndash 2 2 ndash ndash 2Denhamia fournieri subsp Drakeana Celastraceae ndash 1 4 ndash ndash ndash

Monodominance at the rainforest edge Australian Journal of Botany 319

exampleC albicans has relatively thick bark and its investmentin bark thickness is disproportionally higher when the trees aresmall (Ibanez et al 2013b) enhancing its probability ofestablishment in fire-prone ecosystems (see Jackson et al1999 Lawes et al 2013) Furthermore all Codia species arelikely to be able to resprout after fire enhancing the probabilityof persistence in fire-prone ecosystems (Gignoux et al 1997Higgins et al 2000) Resprouting has been observed forC discolour and C nitida in maquis (Jaffre et al 1998b) andfor C albicans and C montana in savannas (Ibanez 2012) CMis also possibly pre-adapted to poor-nutrient soils giving it acompetitive advantage (Pillon et al 2009)

Conclusions

The monodominance of CM is clearly an early and non-persistent step in the secondary succession from savanna tomixed rainforest Given our state of knowledge it is difficult toidentify which combination of traits and environmental conditionslead to the monodominance of CM Monodominance in earlysuccession often results from a disturbance such as fire and thepresence of a species well adapted to and able to rapidly occupythe disturbed environment It is crucial to understand suchvegetation dynamics in order to effectively manage these areasHere rather than preventing recovery CM likely allowed aquick closure of anthropogenic savannas followed by a slowrecovery of diversity toward a mixed rainforest Moststudies have focussed on the ecosystem lsquoconsequencesrsquo ofmonodominant forest (eg Torti et al 2001 Brookshire andThomas 2013) but species such as CM that are able to rapidlyoccupy a disturbed environment and even form monodominantforest may provide ecosystem lsquobenefitsrsquo for example by limitingsoil erosion and maintaining soil quality

Acknowledgements

This work was funded by the Southern Province of New Caledonia(C 315-12) We thank the personnel of the provincial park Parc desGrands Fougegraveres for their hospitality and logistical support as well as thestaff of Noumeacutearsquos herbarium of IRD We are grateful to Juliane KaohGendrilla Warimavute Paul Birmbaum and Michegravele Magat for help withfieldwork andCeacutelineChambreyVanessaHequet andHerveacuteVandrot for plantidentification We thank Jennifer Read Tanguy Jaffreacute Lynda Prior as well astwo anonymous reviewers for their valuable comments on the manuscript

References

Brookshire ENJ Thomas SA (2013) Ecosystem consequences of treemonodominance for nitrogen cycling in lowland tropical forest PLoSONE 8 1ndash7

Chatain A Read J Jaffre T (2009) Does leaf-level nutrient-use efficiencyexplain Nothofagus-dominance of some tropical rain forests in NewCaledonia Plant Ecology 201 51ndash66 doi101007s11258-008-9477-z

Connell JH Lowman MD (1989) Low-diversity tropical rain forests ndash somepossible mechanisms for their existence American Naturalist 13488ndash119 doi101086284967

DegagneRSHenkel TW Steinberg SJ Fox Iii L (2009) IdentifyingDicymbecorymbosa monodominant forests in Guyana using satellite imageryBiotropica 41 7ndash15 doi101111j1744-7429200800446x

Fonty E Molino J-F Prevost M-F Sabatier D (2011) A new case ofneotropical monodominant forest Spirotropis longifolia

(LeguminosaendashPapilionoideae) in French Guiana Journal of TropicalEcology 27 641ndash644 doi101017S0266467411000356

Gignoux J Clobert J Menaut JC (1997) Alternative fire resistancestrategies in savanna trees Oecologia 110 576ndash583doi101007s004420050198

Greene DF Johnson EA (1989) A model of wind dispersal of winged orplumed seeds Ecology 70 339ndash347 doi1023071937538

Hart TB (1990) Monospecific dominance in tropical rain forests Trends inEcology amp Evolution 5 6ndash11 doi1010160169-5347(90)90005-X

Hart TB Hart JA Murphy PG (1989) Monodominant and species-richforests of the humid tropics causes for their co-occurrence AmericanNaturalist 133 613ndash633 doi101086284941

Henkel TW (2003) Monodominance in the ectomycorrhizal Dicymbecorymbosa (Caesalpiniaceae) from Guyana Journal of TropicalEcology 19 417ndash437 doi101017S0266467403003468

Higgins SI Bond WJ Trollope WSW (2000) Fire resprouting andvariability a recipe for grass-tree coexistence in savanna Journal ofEcology 88 213ndash229 doi101046j1365-2745200000435x

Hopkins HCF (2005) Nomenclature and typification in the endemic genusCodia (Cunoniaceae) from New Caledonia Adansonia 27 243ndash254

Hopkins HCF Fogliani B Pillon Y (2007) Four new species in the endemicgenus Codia (Cunoniaceae) from New Caledonia Kew Bulletin 62259ndash274

Ibanez T (2012) lsquoDynamique des forecircts denses humides et des savanes enreacuteponse aux incendies en Nouvelle-Caleacutedoniersquo Rainforest and savannadynamics in response to fires in New Caledonia (Universiteacute Aix-Marseille Aix en Provence France)

Ibanez T Heacutely C Curt T Gaucherel C (2012) Sharp transitions ofmicroclimatic conditions between savanna and forest in NewCaledonia insights into vulnerability of forest edges to fire AustralEcology doi101111aec12015

Ibanez T Borgniet L Mangeas M Gaucherel C Geacuteraux H Heacutely C (2013a)Rainforest and savanna landscape dynamics in New Caledonia towardsa mosaic of stable rainforest and savanna states Austral Ecology 3833ndash45 doi101111j1442-9993201202369x

Ibanez T Curt T Heacutely C (2013b) Low tolerance of New Caledoniansecondary forest species to savanna fires Journal of VegetationScience 24 177ndash188 doi101111j1654-1103201201448x

Ibanez TMunzinger J Dagostini G Hequet V Rigault F Jaffreacute T BirnbaumP (2014) Structural and floristic diversity of mixed tropical rain forest inNew Caledonia new data from the New Caledonian Plant Inventoryand Permanent Plot Network (NC-PIPPN) Applied Vegetation Science17 386ndash397

Ibanez T Munzinger J Gaucherel C Curt T Heacutely C (2013c) Inferringsavannah-rainforest boundary dynamics from vegetation structure andcomposition a case study in New Caledonia Australian Journal ofBotany 61 128ndash138 doi101071BT12255

Jackson JF Adams DC Jackson UB (1999) Allometry of constitutivedefense a model and a comparative test with tree bark and fire regimeAmerican Naturalist 153 614ndash632 doi101086303201

Jaffreacute T Bouchet P Veillon JM (1998a) Threatened plants of NewCaledonia is the system of protected areas adequate Biodiversity andConservation 7 109ndash135 doi101023A1008815930865

Jaffre T Rigault F Dagostini G (1998b) Impact des feux de brousse surles maquis ligno-herbaceacutes des roches ultramafiques de Nouvelle-Caleacutedonie Adansonia 20 173ndash189

Lawes MJ Midgley JJ Clarke PJ (2013) Costs and benefits of relative barkthickness in relation to fire damage a savannaforest contrast Journalof Ecology 101 517ndash524 doi1011111365-274512035

Marimon BS Felfili JM Fagg CW Marimon-Junior BH Umetsu RKOliveira-Santos C Morandi PS Lima HS Terra Nascimento AR(2012) Monodominance in a forest of Brosimum rubescens Taub(Moraceae) structure and dynamics of natural regeneration ActaOecologica 43 134ndash139 doi101016jactao201207001

320 Australian Journal of Botany T Ibanez and P Birnbaum

inventoried in the undergrowth of SAMPLE-1 This regenerationpool was by far dominated by forest species (94 of the smalltrees and 99 of the seedlings) Regeneration of CM was scarce(3 small trees and 19 seedlings located in only 3 and 7 of the 37sample points respectively) and neither MQ small trees norseedlings were observed in the undergrowth No clearrelationships between the characteristics of the CM canopy-level population and regeneration pool were detected

In contrast in SAMPLE-2 many CM small trees wererecorded in the undergrowth of the CM canopy-levelpopulation (Fig 3fndashj) Nevertheless compared with thecanopy-level population the extent and the relative dominancein the undergrowth decreased as the dominance of other forestspecies increased Only 10 of the 393 inventoried seedlingswere CM (81 were forest species and 9 were MQ) CMseedlings were found both under CM canopy and in opensavanna (up to 172m in front of the forest edge) at similardensities (015 seedlings mndash2 on average Wilcoxon testP-value gt005) Conversely MQ seedlings were found only insavannas (Fig 3kndasho) Seedlings of forest species occurredall along transects and their number increased significantly(chi-square test P-value lt0001) from savanna to mixed forest

(8 in savanna 36 in the CM population and 56 in themixed forest)

Species richness and species composition patterns

Despite the dominance of CM 121 taxa belonging to 50families were identified (24 trees were not identified seeAppendix S1 available as Supplementary Material for thispaper) In SAMPLE-1 canopy-level species richness wasnegatively correlated with RDENSCM (Fig 6a b) In samplingpoints where CM occurred species richness ranged from 3 fora RDENSCM of 094 to 23 for a RDENSCM of 004 whereasspecies richness reached up to 30 in adjacent mixed forestOverall the spatial pattern of species richness in SAMPLE-1suggested that species richness increased from CM populationslocated on the ridges and upslope to mixed rainforest locateddownslope This pattern was highlighted in the SAMPLE-2with species richness increasing from savanna located upslopeor on the ridges to mixed forest located downslope (Fig 7) Theprofiles of species richness and cumulative number of specieswere not affected by the CM population

Interpreting floristic composition was difficult because ofthe overall rarity of species in both samplings Only 31 specieswere represented by more than 10 trees and only 23 of themwere inventoried in both samplings In SAMPLE-1 NMDShighlighted gradual changes rather than clearly distinct plantcomposition Distribution of the most common species alongtransects (Table 1) suggested that no species were able to growin all three compartments of our transects However mostspecies occurred either in savannandashCM interface or theCM-mixed forest one As a result the canopy between the

(a) (b)10

06

04

02

0

RD

EN

SC

M250

200

150

100

50

0Fr

eque

ncy

10 20 30 40 50 60 70 80

DBHCM

08

20 40 60DBHCM

80 100

Fig 4 Populations size structure of Codia mackeeana trees (CM) inSAMPLE-1 (a) Diameter at breast height of CM (DBHCM) as a functionof the relative density of CM (RDENSCM) points represent the median valueand bars the 1st and 3rd quartiles intervals (the grey tone of the points isproportional to RDENSCM) Median values were significantly smaller whenRDENSCM05 (Wilcoxon rank sums test Plt 0001) (b) Histogram ofthe distribution of DBHCM all sampling points for which RDENSCM05pooled together

20

60

50

40

30

20

10

40

Position along the transect (m)

DB

HC

M

60 80

T1T2T3T4

T5

Fig 5 Size distribution of Codia mackeeana (DBHCM) according tothe position of the trees along the transects (Pearsonrsquos r= 034 P-valuelt0001) Dark solid line represents linear quantile regression for q= 05(median y= 020x+ 847) and grey polygon represents the intervalbetween the linear quantile regressions for q= 025 and q= 075 Thevertical black line represents the forestndashsavanna edge

Monodominance at the rainforest edge Australian Journal of Botany 317

savanna and the mixed forest although dominated by CMconsisted of a mixture of pioneer species such Myodocarpusspecies (mostly found close to the savanna) as well as foresttree species such as Garcinia virgata Plerandra pancheri orCalophyllum caledonicum (mostly found close to the mixedforest) Additional small trees such as Guioa glauca orDiospyros olen enriched the undergrowth

Discussion

Monodominance of C mackeeanea a step in thesuccessional process

Our results suggest that the observed CM populations constitutean early and non-persistent step in the process of successionfrom savanna to mixed tropical rainforest The studied patch of

1657635

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

1657645

Longitude (DD) 1-RDENSCM NDMS11657655 00 02 04 06 08 10 ndash04 ndash02 00 02 04

Latit

ude

(DD

)

R2 = 072lowastlowastlowast FOR

20

15

10

5

Spe

cies

ric

hnes

s

04

02

00

ndash02

ndash04

ND

MS

2

(c)(b)

y = 41 + 148

lowast x

MQ

CM

Stress = 015(a)

430

440450

460

470

430

440420

440

Fig 6 Distribution of species richness and relationship with relative density ofCodia mackeeana (RDENSCM) in the SAMPLE-1 point size is proportional tospecies richness and point colour is proportional to RDENSCM (linear grey scales white for RDENSCM= 0 and black for RDENSCM= 1 (a) Map of samplingpoints contour lines represent elevation isoclines (10m) (b) Linear relationship between species richness andRDENSCM (sampling points where RDENSCM= 0were removed) (c) Ordination of sampling points using non-metric multidimensional scaling (non-metric multidimensional scaling 2D-solution) CMindicates points where RDENSCM05 MQ points where alive Melaleuca quiquenervia were inventoried but no C mackeeanea and FOR mixed forestpoints where neither C mackeeanea nor M quinquenervia were inventoried

Transect 1

Transect 4 Transect 5

Transect 2 Transect 3

0 10 20 30 40 50 60

0 20 40 60 80 100

Position along the transect (m)

0 10 20 30 40 50 60

0 10 20 30 40 50 60 0 10 20 30 40 5070

40

30

20

10

0

40

30

20

10

0

Spe

cies

ric

hnes

s amp

cum

ulat

ive

num

ber

of s

peci

es

Fig 7 Smoothed local species richness (black lines) and cumulative number of species (dotted lines) along the five studied transects (trees and small treespooled together) Vertical black lines represent first and last inventoried Codia mackeeana (CM) along the transects and grey areas represent areamonodominated by CM (ie RDENSCM gt 05) Bold black lines represent significative (Pgt 0005) linear relationships between species richness and theposition along the transects across the CM population

318 Australian Journal of Botany T Ibanez and P Birnbaum

CM within a matrix of mixed tropical rainforest (SAMPLE-1)is likely to result from the margin expansion of CM forestfrom mixed forest edges toward savanna (SAMPLE-2) Thepresence of remnant MQ savanna trees a shade-intolerantspecies (Serbesoff-King 2003) in the CM tree populationsindicates that this species occurred in the savannas before theestablishment of CM (Ibanez et al 2013c) This hypothesis issupported by the presence of seedlings and small trees of CMin savannas (SAMPLE-2)

The recruitment pool under CM canopy was stronglydominated by mixed forest species which suggests thatmonodominance will not persist one more generation in theabsence of disturbance (Connell and Lowman 1989 Hart1990) Although CM small trees and seedlings were veryscarce in SAMPLE-1 they were substantially more abundantin places where light availability was higher as in tree gaps(SAMPLE-1 T Ibanez pers obs) or near the forest edge(SAMPLE-2) This is consistent with prolific seedlinggermination of shade-intolerant species following canopyopening (eg by tree fall or defoliation) (Marimon et al 2012Read and Jaffre 2013) Nevertheless as shown by Newberyet al (2013) the openness created by the fall of a single treemay be insufficient to allow the recruitment in the canopy level

The spatial pattern of species richness and the analysis ofspecies composition suggest that mixed rainforest will succeedto CM population by margin expansion At middle elevationsthe landscape of New Caledonia mainly consists of a mosaic ofsavannas (or maquis on ultramafic substrates) maintained bybush fires and remnant rainforest patches in valleys and gullies(ie valley path see Jaffreacute et al 1998a Ibanez et al 2013a)In contrast to New Caledonian Nothofagus which establishesin mixed forest areas after severe disturbance (Read and Jaffre2013) our results showed that CM can establish in opensavanna and thus initiate forest recovery The pattern of CMdominance and species richness in SAMPLE-1 suggests that theestablishment of CM and the subsequent enrichment of mixedforest species begin at the edge of forest located along valleysand gullies and then progressively extends toward the crest

(see also Ibanez et al 2013a) The formation of belt of CMalong forest edges (SAMPLE-2) is likely to be due to mostfavourable conditions for the establishment of CM trees thereIndeed relativelywet conditions in the savanna close to the forestedge may promote forest expansion by limiting fire spread(Ibanez et al 2012)

Drivers of C mackeeana dominance

Monodominance during early stages of succession is widelyattributed to the massive establishment of a single highlyvagile and rapidly growing species (Hart 1990) The small sizerange of CM in locations where it was dominant suggests thatits dominance results from massive establishment of a singlecohort Codia may fit to this model as it produces indehiscentfruits with many woolly wind-dispersed seeds (Hopkins 2005)However many others species located in the study area(including other Cunoniaceae) possess these traits but do notproduce monodominant forests (see Ibanez 2012) Peh et al(2011) stated that poor seed dispersal leading to gregarioushabit is one mechanism that favours monodominance

The main plant attributes acting on dispersal pattern ofwind-dispersed seeds are the aerodynamic properties ofdiaspores and the height from which they are released (Greeneand Johnson 1989 Nathan et al 2001 Muller-Landau et al2008) Although wind-dispersed seeds may be dispersed faraway most seeds are dispersed close to the parent treeespecially if it is not tall Field observations showed thatCodia is likely to be fertile very early in its ontogeny and thusrapidly disperses seeds from a low height (lt5m) after itsestablishment in an open area This leads to the formation ofdense thickets of CM shrubs which may exclude theestablishment of other species and promote the developmentof CM monodominant forest

Monodominance is also promoted by competitive advantages(Peh et al 2011) such as adaptation to the frequent fire andpoor-nutrient soils of this study system Codia species have acombination of traits that allow them to tolerate fire For

Table 1 Number of trees (diameter at breat height (DBH)$10 cm) and small trees (5 DBHlt 10 cm) of the15 most common species in the three compartments of transects savanna (S) Codia mackeeana population (C) and

mixed rainforest (F)

Species Family Trees Small treesS C F S C F

Codia mackeeana Cunoniaceae 4 125 ndash 5 49 2Melaleuca quinquenervia Myrtaceae 47 12 ndash 104 15 ndash

Myodocarpus sp Myodocarpaceae 2 13 ndash 10 27 1Garcinia virgata Clusiaceae ndash 9 6 ndash 13 2Plerandra pancheri Araliaceae ndash 13 7 ndash 4 1Calophyllum caledonicum Calophyllaceae ndash 7 14 ndash ndash ndash

Myodocarpus pinnatus Myodocarpaceae ndash 11 2 2 3 ndash

Myrsine arborea Primulaceae ndash 4 5 ndash ndash 4Storthocalyx sp Sapindaceae ndash ndash 8 ndash 3 2Styphelia cf cymbulae Ericaceae ndash 2 ndash ndash 3 5Diospyros olen Ebenaceae ndash ndash 1 ndash 2 4Guioa glauca Sapindaceae ndash ndash 2 ndash 4 ndash

Weinmannia serrata Cunoniaceae ndash 4 ndash 2 ndash

Podocarpus sylvestris Podocarpaceae ndash 2 2 ndash ndash 2Denhamia fournieri subsp Drakeana Celastraceae ndash 1 4 ndash ndash ndash

Monodominance at the rainforest edge Australian Journal of Botany 319

exampleC albicans has relatively thick bark and its investmentin bark thickness is disproportionally higher when the trees aresmall (Ibanez et al 2013b) enhancing its probability ofestablishment in fire-prone ecosystems (see Jackson et al1999 Lawes et al 2013) Furthermore all Codia species arelikely to be able to resprout after fire enhancing the probabilityof persistence in fire-prone ecosystems (Gignoux et al 1997Higgins et al 2000) Resprouting has been observed forC discolour and C nitida in maquis (Jaffre et al 1998b) andfor C albicans and C montana in savannas (Ibanez 2012) CMis also possibly pre-adapted to poor-nutrient soils giving it acompetitive advantage (Pillon et al 2009)

Conclusions

The monodominance of CM is clearly an early and non-persistent step in the secondary succession from savanna tomixed rainforest Given our state of knowledge it is difficult toidentify which combination of traits and environmental conditionslead to the monodominance of CM Monodominance in earlysuccession often results from a disturbance such as fire and thepresence of a species well adapted to and able to rapidly occupythe disturbed environment It is crucial to understand suchvegetation dynamics in order to effectively manage these areasHere rather than preventing recovery CM likely allowed aquick closure of anthropogenic savannas followed by a slowrecovery of diversity toward a mixed rainforest Moststudies have focussed on the ecosystem lsquoconsequencesrsquo ofmonodominant forest (eg Torti et al 2001 Brookshire andThomas 2013) but species such as CM that are able to rapidlyoccupy a disturbed environment and even form monodominantforest may provide ecosystem lsquobenefitsrsquo for example by limitingsoil erosion and maintaining soil quality

Acknowledgements

This work was funded by the Southern Province of New Caledonia(C 315-12) We thank the personnel of the provincial park Parc desGrands Fougegraveres for their hospitality and logistical support as well as thestaff of Noumeacutearsquos herbarium of IRD We are grateful to Juliane KaohGendrilla Warimavute Paul Birmbaum and Michegravele Magat for help withfieldwork andCeacutelineChambreyVanessaHequet andHerveacuteVandrot for plantidentification We thank Jennifer Read Tanguy Jaffreacute Lynda Prior as well astwo anonymous reviewers for their valuable comments on the manuscript

References

Brookshire ENJ Thomas SA (2013) Ecosystem consequences of treemonodominance for nitrogen cycling in lowland tropical forest PLoSONE 8 1ndash7

Chatain A Read J Jaffre T (2009) Does leaf-level nutrient-use efficiencyexplain Nothofagus-dominance of some tropical rain forests in NewCaledonia Plant Ecology 201 51ndash66 doi101007s11258-008-9477-z

Connell JH Lowman MD (1989) Low-diversity tropical rain forests ndash somepossible mechanisms for their existence American Naturalist 13488ndash119 doi101086284967

DegagneRSHenkel TW Steinberg SJ Fox Iii L (2009) IdentifyingDicymbecorymbosa monodominant forests in Guyana using satellite imageryBiotropica 41 7ndash15 doi101111j1744-7429200800446x

Fonty E Molino J-F Prevost M-F Sabatier D (2011) A new case ofneotropical monodominant forest Spirotropis longifolia

(LeguminosaendashPapilionoideae) in French Guiana Journal of TropicalEcology 27 641ndash644 doi101017S0266467411000356

Gignoux J Clobert J Menaut JC (1997) Alternative fire resistancestrategies in savanna trees Oecologia 110 576ndash583doi101007s004420050198

Greene DF Johnson EA (1989) A model of wind dispersal of winged orplumed seeds Ecology 70 339ndash347 doi1023071937538

Hart TB (1990) Monospecific dominance in tropical rain forests Trends inEcology amp Evolution 5 6ndash11 doi1010160169-5347(90)90005-X

Hart TB Hart JA Murphy PG (1989) Monodominant and species-richforests of the humid tropics causes for their co-occurrence AmericanNaturalist 133 613ndash633 doi101086284941

Henkel TW (2003) Monodominance in the ectomycorrhizal Dicymbecorymbosa (Caesalpiniaceae) from Guyana Journal of TropicalEcology 19 417ndash437 doi101017S0266467403003468

Higgins SI Bond WJ Trollope WSW (2000) Fire resprouting andvariability a recipe for grass-tree coexistence in savanna Journal ofEcology 88 213ndash229 doi101046j1365-2745200000435x

Hopkins HCF (2005) Nomenclature and typification in the endemic genusCodia (Cunoniaceae) from New Caledonia Adansonia 27 243ndash254

Hopkins HCF Fogliani B Pillon Y (2007) Four new species in the endemicgenus Codia (Cunoniaceae) from New Caledonia Kew Bulletin 62259ndash274

Ibanez T (2012) lsquoDynamique des forecircts denses humides et des savanes enreacuteponse aux incendies en Nouvelle-Caleacutedoniersquo Rainforest and savannadynamics in response to fires in New Caledonia (Universiteacute Aix-Marseille Aix en Provence France)

Ibanez T Heacutely C Curt T Gaucherel C (2012) Sharp transitions ofmicroclimatic conditions between savanna and forest in NewCaledonia insights into vulnerability of forest edges to fire AustralEcology doi101111aec12015

Ibanez T Borgniet L Mangeas M Gaucherel C Geacuteraux H Heacutely C (2013a)Rainforest and savanna landscape dynamics in New Caledonia towardsa mosaic of stable rainforest and savanna states Austral Ecology 3833ndash45 doi101111j1442-9993201202369x

Ibanez T Curt T Heacutely C (2013b) Low tolerance of New Caledoniansecondary forest species to savanna fires Journal of VegetationScience 24 177ndash188 doi101111j1654-1103201201448x

Ibanez TMunzinger J Dagostini G Hequet V Rigault F Jaffreacute T BirnbaumP (2014) Structural and floristic diversity of mixed tropical rain forest inNew Caledonia new data from the New Caledonian Plant Inventoryand Permanent Plot Network (NC-PIPPN) Applied Vegetation Science17 386ndash397

Ibanez T Munzinger J Gaucherel C Curt T Heacutely C (2013c) Inferringsavannah-rainforest boundary dynamics from vegetation structure andcomposition a case study in New Caledonia Australian Journal ofBotany 61 128ndash138 doi101071BT12255

Jackson JF Adams DC Jackson UB (1999) Allometry of constitutivedefense a model and a comparative test with tree bark and fire regimeAmerican Naturalist 153 614ndash632 doi101086303201

Jaffreacute T Bouchet P Veillon JM (1998a) Threatened plants of NewCaledonia is the system of protected areas adequate Biodiversity andConservation 7 109ndash135 doi101023A1008815930865

Jaffre T Rigault F Dagostini G (1998b) Impact des feux de brousse surles maquis ligno-herbaceacutes des roches ultramafiques de Nouvelle-Caleacutedonie Adansonia 20 173ndash189

Lawes MJ Midgley JJ Clarke PJ (2013) Costs and benefits of relative barkthickness in relation to fire damage a savannaforest contrast Journalof Ecology 101 517ndash524 doi1011111365-274512035

Marimon BS Felfili JM Fagg CW Marimon-Junior BH Umetsu RKOliveira-Santos C Morandi PS Lima HS Terra Nascimento AR(2012) Monodominance in a forest of Brosimum rubescens Taub(Moraceae) structure and dynamics of natural regeneration ActaOecologica 43 134ndash139 doi101016jactao201207001

320 Australian Journal of Botany T Ibanez and P Birnbaum

savanna and the mixed forest although dominated by CMconsisted of a mixture of pioneer species such Myodocarpusspecies (mostly found close to the savanna) as well as foresttree species such as Garcinia virgata Plerandra pancheri orCalophyllum caledonicum (mostly found close to the mixedforest) Additional small trees such as Guioa glauca orDiospyros olen enriched the undergrowth

Discussion

Monodominance of C mackeeanea a step in thesuccessional process

Our results suggest that the observed CM populations constitutean early and non-persistent step in the process of successionfrom savanna to mixed tropical rainforest The studied patch of

1657635

ndash21

6240

ndash21

6230

ndash21

6220

ndash21

6210

1657645

Longitude (DD) 1-RDENSCM NDMS11657655 00 02 04 06 08 10 ndash04 ndash02 00 02 04

Latit

ude

(DD

)

R2 = 072lowastlowastlowast FOR

20

15

10

5

Spe

cies

ric

hnes

s

04

02

00

ndash02

ndash04

ND

MS

2

(c)(b)

y = 41 + 148

lowast x

MQ

CM

Stress = 015(a)

430

440450

460

470

430

440420

440

Fig 6 Distribution of species richness and relationship with relative density ofCodia mackeeana (RDENSCM) in the SAMPLE-1 point size is proportional tospecies richness and point colour is proportional to RDENSCM (linear grey scales white for RDENSCM= 0 and black for RDENSCM= 1 (a) Map of samplingpoints contour lines represent elevation isoclines (10m) (b) Linear relationship between species richness andRDENSCM (sampling points where RDENSCM= 0were removed) (c) Ordination of sampling points using non-metric multidimensional scaling (non-metric multidimensional scaling 2D-solution) CMindicates points where RDENSCM05 MQ points where alive Melaleuca quiquenervia were inventoried but no C mackeeanea and FOR mixed forestpoints where neither C mackeeanea nor M quinquenervia were inventoried

Transect 1

Transect 4 Transect 5

Transect 2 Transect 3

0 10 20 30 40 50 60

0 20 40 60 80 100

Position along the transect (m)

0 10 20 30 40 50 60

0 10 20 30 40 50 60 0 10 20 30 40 5070

40

30

20

10

0

40

30

20

10

0

Spe

cies

ric

hnes

s amp

cum

ulat

ive

num

ber

of s

peci

es

Fig 7 Smoothed local species richness (black lines) and cumulative number of species (dotted lines) along the five studied transects (trees and small treespooled together) Vertical black lines represent first and last inventoried Codia mackeeana (CM) along the transects and grey areas represent areamonodominated by CM (ie RDENSCM gt 05) Bold black lines represent significative (Pgt 0005) linear relationships between species richness and theposition along the transects across the CM population

318 Australian Journal of Botany T Ibanez and P Birnbaum

CM within a matrix of mixed tropical rainforest (SAMPLE-1)is likely to result from the margin expansion of CM forestfrom mixed forest edges toward savanna (SAMPLE-2) Thepresence of remnant MQ savanna trees a shade-intolerantspecies (Serbesoff-King 2003) in the CM tree populationsindicates that this species occurred in the savannas before theestablishment of CM (Ibanez et al 2013c) This hypothesis issupported by the presence of seedlings and small trees of CMin savannas (SAMPLE-2)

The recruitment pool under CM canopy was stronglydominated by mixed forest species which suggests thatmonodominance will not persist one more generation in theabsence of disturbance (Connell and Lowman 1989 Hart1990) Although CM small trees and seedlings were veryscarce in SAMPLE-1 they were substantially more abundantin places where light availability was higher as in tree gaps(SAMPLE-1 T Ibanez pers obs) or near the forest edge(SAMPLE-2) This is consistent with prolific seedlinggermination of shade-intolerant species following canopyopening (eg by tree fall or defoliation) (Marimon et al 2012Read and Jaffre 2013) Nevertheless as shown by Newberyet al (2013) the openness created by the fall of a single treemay be insufficient to allow the recruitment in the canopy level

The spatial pattern of species richness and the analysis ofspecies composition suggest that mixed rainforest will succeedto CM population by margin expansion At middle elevationsthe landscape of New Caledonia mainly consists of a mosaic ofsavannas (or maquis on ultramafic substrates) maintained bybush fires and remnant rainforest patches in valleys and gullies(ie valley path see Jaffreacute et al 1998a Ibanez et al 2013a)In contrast to New Caledonian Nothofagus which establishesin mixed forest areas after severe disturbance (Read and Jaffre2013) our results showed that CM can establish in opensavanna and thus initiate forest recovery The pattern of CMdominance and species richness in SAMPLE-1 suggests that theestablishment of CM and the subsequent enrichment of mixedforest species begin at the edge of forest located along valleysand gullies and then progressively extends toward the crest

(see also Ibanez et al 2013a) The formation of belt of CMalong forest edges (SAMPLE-2) is likely to be due to mostfavourable conditions for the establishment of CM trees thereIndeed relativelywet conditions in the savanna close to the forestedge may promote forest expansion by limiting fire spread(Ibanez et al 2012)

Drivers of C mackeeana dominance

Monodominance during early stages of succession is widelyattributed to the massive establishment of a single highlyvagile and rapidly growing species (Hart 1990) The small sizerange of CM in locations where it was dominant suggests thatits dominance results from massive establishment of a singlecohort Codia may fit to this model as it produces indehiscentfruits with many woolly wind-dispersed seeds (Hopkins 2005)However many others species located in the study area(including other Cunoniaceae) possess these traits but do notproduce monodominant forests (see Ibanez 2012) Peh et al(2011) stated that poor seed dispersal leading to gregarioushabit is one mechanism that favours monodominance

The main plant attributes acting on dispersal pattern ofwind-dispersed seeds are the aerodynamic properties ofdiaspores and the height from which they are released (Greeneand Johnson 1989 Nathan et al 2001 Muller-Landau et al2008) Although wind-dispersed seeds may be dispersed faraway most seeds are dispersed close to the parent treeespecially if it is not tall Field observations showed thatCodia is likely to be fertile very early in its ontogeny and thusrapidly disperses seeds from a low height (lt5m) after itsestablishment in an open area This leads to the formation ofdense thickets of CM shrubs which may exclude theestablishment of other species and promote the developmentof CM monodominant forest

Monodominance is also promoted by competitive advantages(Peh et al 2011) such as adaptation to the frequent fire andpoor-nutrient soils of this study system Codia species have acombination of traits that allow them to tolerate fire For

Table 1 Number of trees (diameter at breat height (DBH)$10 cm) and small trees (5 DBHlt 10 cm) of the15 most common species in the three compartments of transects savanna (S) Codia mackeeana population (C) and

mixed rainforest (F)

Species Family Trees Small treesS C F S C F

Codia mackeeana Cunoniaceae 4 125 ndash 5 49 2Melaleuca quinquenervia Myrtaceae 47 12 ndash 104 15 ndash

Myodocarpus sp Myodocarpaceae 2 13 ndash 10 27 1Garcinia virgata Clusiaceae ndash 9 6 ndash 13 2Plerandra pancheri Araliaceae ndash 13 7 ndash 4 1Calophyllum caledonicum Calophyllaceae ndash 7 14 ndash ndash ndash

Myodocarpus pinnatus Myodocarpaceae ndash 11 2 2 3 ndash

Myrsine arborea Primulaceae ndash 4 5 ndash ndash 4Storthocalyx sp Sapindaceae ndash ndash 8 ndash 3 2Styphelia cf cymbulae Ericaceae ndash 2 ndash ndash 3 5Diospyros olen Ebenaceae ndash ndash 1 ndash 2 4Guioa glauca Sapindaceae ndash ndash 2 ndash 4 ndash

Weinmannia serrata Cunoniaceae ndash 4 ndash 2 ndash

Podocarpus sylvestris Podocarpaceae ndash 2 2 ndash ndash 2Denhamia fournieri subsp Drakeana Celastraceae ndash 1 4 ndash ndash ndash

Monodominance at the rainforest edge Australian Journal of Botany 319

exampleC albicans has relatively thick bark and its investmentin bark thickness is disproportionally higher when the trees aresmall (Ibanez et al 2013b) enhancing its probability ofestablishment in fire-prone ecosystems (see Jackson et al1999 Lawes et al 2013) Furthermore all Codia species arelikely to be able to resprout after fire enhancing the probabilityof persistence in fire-prone ecosystems (Gignoux et al 1997Higgins et al 2000) Resprouting has been observed forC discolour and C nitida in maquis (Jaffre et al 1998b) andfor C albicans and C montana in savannas (Ibanez 2012) CMis also possibly pre-adapted to poor-nutrient soils giving it acompetitive advantage (Pillon et al 2009)

Conclusions

The monodominance of CM is clearly an early and non-persistent step in the secondary succession from savanna tomixed rainforest Given our state of knowledge it is difficult toidentify which combination of traits and environmental conditionslead to the monodominance of CM Monodominance in earlysuccession often results from a disturbance such as fire and thepresence of a species well adapted to and able to rapidly occupythe disturbed environment It is crucial to understand suchvegetation dynamics in order to effectively manage these areasHere rather than preventing recovery CM likely allowed aquick closure of anthropogenic savannas followed by a slowrecovery of diversity toward a mixed rainforest Moststudies have focussed on the ecosystem lsquoconsequencesrsquo ofmonodominant forest (eg Torti et al 2001 Brookshire andThomas 2013) but species such as CM that are able to rapidlyoccupy a disturbed environment and even form monodominantforest may provide ecosystem lsquobenefitsrsquo for example by limitingsoil erosion and maintaining soil quality

Acknowledgements

This work was funded by the Southern Province of New Caledonia(C 315-12) We thank the personnel of the provincial park Parc desGrands Fougegraveres for their hospitality and logistical support as well as thestaff of Noumeacutearsquos herbarium of IRD We are grateful to Juliane KaohGendrilla Warimavute Paul Birmbaum and Michegravele Magat for help withfieldwork andCeacutelineChambreyVanessaHequet andHerveacuteVandrot for plantidentification We thank Jennifer Read Tanguy Jaffreacute Lynda Prior as well astwo anonymous reviewers for their valuable comments on the manuscript

References

Brookshire ENJ Thomas SA (2013) Ecosystem consequences of treemonodominance for nitrogen cycling in lowland tropical forest PLoSONE 8 1ndash7

Chatain A Read J Jaffre T (2009) Does leaf-level nutrient-use efficiencyexplain Nothofagus-dominance of some tropical rain forests in NewCaledonia Plant Ecology 201 51ndash66 doi101007s11258-008-9477-z

Connell JH Lowman MD (1989) Low-diversity tropical rain forests ndash somepossible mechanisms for their existence American Naturalist 13488ndash119 doi101086284967

DegagneRSHenkel TW Steinberg SJ Fox Iii L (2009) IdentifyingDicymbecorymbosa monodominant forests in Guyana using satellite imageryBiotropica 41 7ndash15 doi101111j1744-7429200800446x

Fonty E Molino J-F Prevost M-F Sabatier D (2011) A new case ofneotropical monodominant forest Spirotropis longifolia

(LeguminosaendashPapilionoideae) in French Guiana Journal of TropicalEcology 27 641ndash644 doi101017S0266467411000356

Gignoux J Clobert J Menaut JC (1997) Alternative fire resistancestrategies in savanna trees Oecologia 110 576ndash583doi101007s004420050198

Greene DF Johnson EA (1989) A model of wind dispersal of winged orplumed seeds Ecology 70 339ndash347 doi1023071937538

Hart TB (1990) Monospecific dominance in tropical rain forests Trends inEcology amp Evolution 5 6ndash11 doi1010160169-5347(90)90005-X

Hart TB Hart JA Murphy PG (1989) Monodominant and species-richforests of the humid tropics causes for their co-occurrence AmericanNaturalist 133 613ndash633 doi101086284941

Henkel TW (2003) Monodominance in the ectomycorrhizal Dicymbecorymbosa (Caesalpiniaceae) from Guyana Journal of TropicalEcology 19 417ndash437 doi101017S0266467403003468

Higgins SI Bond WJ Trollope WSW (2000) Fire resprouting andvariability a recipe for grass-tree coexistence in savanna Journal ofEcology 88 213ndash229 doi101046j1365-2745200000435x

Hopkins HCF (2005) Nomenclature and typification in the endemic genusCodia (Cunoniaceae) from New Caledonia Adansonia 27 243ndash254

Hopkins HCF Fogliani B Pillon Y (2007) Four new species in the endemicgenus Codia (Cunoniaceae) from New Caledonia Kew Bulletin 62259ndash274

Ibanez T (2012) lsquoDynamique des forecircts denses humides et des savanes enreacuteponse aux incendies en Nouvelle-Caleacutedoniersquo Rainforest and savannadynamics in response to fires in New Caledonia (Universiteacute Aix-Marseille Aix en Provence France)

Ibanez T Heacutely C Curt T Gaucherel C (2012) Sharp transitions ofmicroclimatic conditions between savanna and forest in NewCaledonia insights into vulnerability of forest edges to fire AustralEcology doi101111aec12015

Ibanez T Borgniet L Mangeas M Gaucherel C Geacuteraux H Heacutely C (2013a)Rainforest and savanna landscape dynamics in New Caledonia towardsa mosaic of stable rainforest and savanna states Austral Ecology 3833ndash45 doi101111j1442-9993201202369x

Ibanez T Curt T Heacutely C (2013b) Low tolerance of New Caledoniansecondary forest species to savanna fires Journal of VegetationScience 24 177ndash188 doi101111j1654-1103201201448x

Ibanez TMunzinger J Dagostini G Hequet V Rigault F Jaffreacute T BirnbaumP (2014) Structural and floristic diversity of mixed tropical rain forest inNew Caledonia new data from the New Caledonian Plant Inventoryand Permanent Plot Network (NC-PIPPN) Applied Vegetation Science17 386ndash397

Ibanez T Munzinger J Gaucherel C Curt T Heacutely C (2013c) Inferringsavannah-rainforest boundary dynamics from vegetation structure andcomposition a case study in New Caledonia Australian Journal ofBotany 61 128ndash138 doi101071BT12255

Jackson JF Adams DC Jackson UB (1999) Allometry of constitutivedefense a model and a comparative test with tree bark and fire regimeAmerican Naturalist 153 614ndash632 doi101086303201

Jaffreacute T Bouchet P Veillon JM (1998a) Threatened plants of NewCaledonia is the system of protected areas adequate Biodiversity andConservation 7 109ndash135 doi101023A1008815930865

Jaffre T Rigault F Dagostini G (1998b) Impact des feux de brousse surles maquis ligno-herbaceacutes des roches ultramafiques de Nouvelle-Caleacutedonie Adansonia 20 173ndash189

Lawes MJ Midgley JJ Clarke PJ (2013) Costs and benefits of relative barkthickness in relation to fire damage a savannaforest contrast Journalof Ecology 101 517ndash524 doi1011111365-274512035

Marimon BS Felfili JM Fagg CW Marimon-Junior BH Umetsu RKOliveira-Santos C Morandi PS Lima HS Terra Nascimento AR(2012) Monodominance in a forest of Brosimum rubescens Taub(Moraceae) structure and dynamics of natural regeneration ActaOecologica 43 134ndash139 doi101016jactao201207001

320 Australian Journal of Botany T Ibanez and P Birnbaum

CM within a matrix of mixed tropical rainforest (SAMPLE-1)is likely to result from the margin expansion of CM forestfrom mixed forest edges toward savanna (SAMPLE-2) Thepresence of remnant MQ savanna trees a shade-intolerantspecies (Serbesoff-King 2003) in the CM tree populationsindicates that this species occurred in the savannas before theestablishment of CM (Ibanez et al 2013c) This hypothesis issupported by the presence of seedlings and small trees of CMin savannas (SAMPLE-2)

The recruitment pool under CM canopy was stronglydominated by mixed forest species which suggests thatmonodominance will not persist one more generation in theabsence of disturbance (Connell and Lowman 1989 Hart1990) Although CM small trees and seedlings were veryscarce in SAMPLE-1 they were substantially more abundantin places where light availability was higher as in tree gaps(SAMPLE-1 T Ibanez pers obs) or near the forest edge(SAMPLE-2) This is consistent with prolific seedlinggermination of shade-intolerant species following canopyopening (eg by tree fall or defoliation) (Marimon et al 2012Read and Jaffre 2013) Nevertheless as shown by Newberyet al (2013) the openness created by the fall of a single treemay be insufficient to allow the recruitment in the canopy level

The spatial pattern of species richness and the analysis ofspecies composition suggest that mixed rainforest will succeedto CM population by margin expansion At middle elevationsthe landscape of New Caledonia mainly consists of a mosaic ofsavannas (or maquis on ultramafic substrates) maintained bybush fires and remnant rainforest patches in valleys and gullies(ie valley path see Jaffreacute et al 1998a Ibanez et al 2013a)In contrast to New Caledonian Nothofagus which establishesin mixed forest areas after severe disturbance (Read and Jaffre2013) our results showed that CM can establish in opensavanna and thus initiate forest recovery The pattern of CMdominance and species richness in SAMPLE-1 suggests that theestablishment of CM and the subsequent enrichment of mixedforest species begin at the edge of forest located along valleysand gullies and then progressively extends toward the crest

(see also Ibanez et al 2013a) The formation of belt of CMalong forest edges (SAMPLE-2) is likely to be due to mostfavourable conditions for the establishment of CM trees thereIndeed relativelywet conditions in the savanna close to the forestedge may promote forest expansion by limiting fire spread(Ibanez et al 2012)

Drivers of C mackeeana dominance

Monodominance during early stages of succession is widelyattributed to the massive establishment of a single highlyvagile and rapidly growing species (Hart 1990) The small sizerange of CM in locations where it was dominant suggests thatits dominance results from massive establishment of a singlecohort Codia may fit to this model as it produces indehiscentfruits with many woolly wind-dispersed seeds (Hopkins 2005)However many others species located in the study area(including other Cunoniaceae) possess these traits but do notproduce monodominant forests (see Ibanez 2012) Peh et al(2011) stated that poor seed dispersal leading to gregarioushabit is one mechanism that favours monodominance

The main plant attributes acting on dispersal pattern ofwind-dispersed seeds are the aerodynamic properties ofdiaspores and the height from which they are released (Greeneand Johnson 1989 Nathan et al 2001 Muller-Landau et al2008) Although wind-dispersed seeds may be dispersed faraway most seeds are dispersed close to the parent treeespecially if it is not tall Field observations showed thatCodia is likely to be fertile very early in its ontogeny and thusrapidly disperses seeds from a low height (lt5m) after itsestablishment in an open area This leads to the formation ofdense thickets of CM shrubs which may exclude theestablishment of other species and promote the developmentof CM monodominant forest

Monodominance is also promoted by competitive advantages(Peh et al 2011) such as adaptation to the frequent fire andpoor-nutrient soils of this study system Codia species have acombination of traits that allow them to tolerate fire For

Table 1 Number of trees (diameter at breat height (DBH)$10 cm) and small trees (5 DBHlt 10 cm) of the15 most common species in the three compartments of transects savanna (S) Codia mackeeana population (C) and

mixed rainforest (F)

Species Family Trees Small treesS C F S C F

Codia mackeeana Cunoniaceae 4 125 ndash 5 49 2Melaleuca quinquenervia Myrtaceae 47 12 ndash 104 15 ndash

Myodocarpus sp Myodocarpaceae 2 13 ndash 10 27 1Garcinia virgata Clusiaceae ndash 9 6 ndash 13 2Plerandra pancheri Araliaceae ndash 13 7 ndash 4 1Calophyllum caledonicum Calophyllaceae ndash 7 14 ndash ndash ndash

Myodocarpus pinnatus Myodocarpaceae ndash 11 2 2 3 ndash

Myrsine arborea Primulaceae ndash 4 5 ndash ndash 4Storthocalyx sp Sapindaceae ndash ndash 8 ndash 3 2Styphelia cf cymbulae Ericaceae ndash 2 ndash ndash 3 5Diospyros olen Ebenaceae ndash ndash 1 ndash 2 4Guioa glauca Sapindaceae ndash ndash 2 ndash 4 ndash

Weinmannia serrata Cunoniaceae ndash 4 ndash 2 ndash

Podocarpus sylvestris Podocarpaceae ndash 2 2 ndash ndash 2Denhamia fournieri subsp Drakeana Celastraceae ndash 1 4 ndash ndash ndash

Monodominance at the rainforest edge Australian Journal of Botany 319

exampleC albicans has relatively thick bark and its investmentin bark thickness is disproportionally higher when the trees aresmall (Ibanez et al 2013b) enhancing its probability ofestablishment in fire-prone ecosystems (see Jackson et al1999 Lawes et al 2013) Furthermore all Codia species arelikely to be able to resprout after fire enhancing the probabilityof persistence in fire-prone ecosystems (Gignoux et al 1997Higgins et al 2000) Resprouting has been observed forC discolour and C nitida in maquis (Jaffre et al 1998b) andfor C albicans and C montana in savannas (Ibanez 2012) CMis also possibly pre-adapted to poor-nutrient soils giving it acompetitive advantage (Pillon et al 2009)

Conclusions

The monodominance of CM is clearly an early and non-persistent step in the secondary succession from savanna tomixed rainforest Given our state of knowledge it is difficult toidentify which combination of traits and environmental conditionslead to the monodominance of CM Monodominance in earlysuccession often results from a disturbance such as fire and thepresence of a species well adapted to and able to rapidly occupythe disturbed environment It is crucial to understand suchvegetation dynamics in order to effectively manage these areasHere rather than preventing recovery CM likely allowed aquick closure of anthropogenic savannas followed by a slowrecovery of diversity toward a mixed rainforest Moststudies have focussed on the ecosystem lsquoconsequencesrsquo ofmonodominant forest (eg Torti et al 2001 Brookshire andThomas 2013) but species such as CM that are able to rapidlyoccupy a disturbed environment and even form monodominantforest may provide ecosystem lsquobenefitsrsquo for example by limitingsoil erosion and maintaining soil quality

Acknowledgements

This work was funded by the Southern Province of New Caledonia(C 315-12) We thank the personnel of the provincial park Parc desGrands Fougegraveres for their hospitality and logistical support as well as thestaff of Noumeacutearsquos herbarium of IRD We are grateful to Juliane KaohGendrilla Warimavute Paul Birmbaum and Michegravele Magat for help withfieldwork andCeacutelineChambreyVanessaHequet andHerveacuteVandrot for plantidentification We thank Jennifer Read Tanguy Jaffreacute Lynda Prior as well astwo anonymous reviewers for their valuable comments on the manuscript

References

Brookshire ENJ Thomas SA (2013) Ecosystem consequences of treemonodominance for nitrogen cycling in lowland tropical forest PLoSONE 8 1ndash7

Chatain A Read J Jaffre T (2009) Does leaf-level nutrient-use efficiencyexplain Nothofagus-dominance of some tropical rain forests in NewCaledonia Plant Ecology 201 51ndash66 doi101007s11258-008-9477-z

Connell JH Lowman MD (1989) Low-diversity tropical rain forests ndash somepossible mechanisms for their existence American Naturalist 13488ndash119 doi101086284967

DegagneRSHenkel TW Steinberg SJ Fox Iii L (2009) IdentifyingDicymbecorymbosa monodominant forests in Guyana using satellite imageryBiotropica 41 7ndash15 doi101111j1744-7429200800446x

Fonty E Molino J-F Prevost M-F Sabatier D (2011) A new case ofneotropical monodominant forest Spirotropis longifolia

(LeguminosaendashPapilionoideae) in French Guiana Journal of TropicalEcology 27 641ndash644 doi101017S0266467411000356

Gignoux J Clobert J Menaut JC (1997) Alternative fire resistancestrategies in savanna trees Oecologia 110 576ndash583doi101007s004420050198

Greene DF Johnson EA (1989) A model of wind dispersal of winged orplumed seeds Ecology 70 339ndash347 doi1023071937538

Hart TB (1990) Monospecific dominance in tropical rain forests Trends inEcology amp Evolution 5 6ndash11 doi1010160169-5347(90)90005-X

Hart TB Hart JA Murphy PG (1989) Monodominant and species-richforests of the humid tropics causes for their co-occurrence AmericanNaturalist 133 613ndash633 doi101086284941

Henkel TW (2003) Monodominance in the ectomycorrhizal Dicymbecorymbosa (Caesalpiniaceae) from Guyana Journal of TropicalEcology 19 417ndash437 doi101017S0266467403003468

Higgins SI Bond WJ Trollope WSW (2000) Fire resprouting andvariability a recipe for grass-tree coexistence in savanna Journal ofEcology 88 213ndash229 doi101046j1365-2745200000435x

Hopkins HCF (2005) Nomenclature and typification in the endemic genusCodia (Cunoniaceae) from New Caledonia Adansonia 27 243ndash254

Hopkins HCF Fogliani B Pillon Y (2007) Four new species in the endemicgenus Codia (Cunoniaceae) from New Caledonia Kew Bulletin 62259ndash274

Ibanez T (2012) lsquoDynamique des forecircts denses humides et des savanes enreacuteponse aux incendies en Nouvelle-Caleacutedoniersquo Rainforest and savannadynamics in response to fires in New Caledonia (Universiteacute Aix-Marseille Aix en Provence France)

Ibanez T Heacutely C Curt T Gaucherel C (2012) Sharp transitions ofmicroclimatic conditions between savanna and forest in NewCaledonia insights into vulnerability of forest edges to fire AustralEcology doi101111aec12015

Ibanez T Borgniet L Mangeas M Gaucherel C Geacuteraux H Heacutely C (2013a)Rainforest and savanna landscape dynamics in New Caledonia towardsa mosaic of stable rainforest and savanna states Austral Ecology 3833ndash45 doi101111j1442-9993201202369x

Ibanez T Curt T Heacutely C (2013b) Low tolerance of New Caledoniansecondary forest species to savanna fires Journal of VegetationScience 24 177ndash188 doi101111j1654-1103201201448x

Ibanez TMunzinger J Dagostini G Hequet V Rigault F Jaffreacute T BirnbaumP (2014) Structural and floristic diversity of mixed tropical rain forest inNew Caledonia new data from the New Caledonian Plant Inventoryand Permanent Plot Network (NC-PIPPN) Applied Vegetation Science17 386ndash397

Ibanez T Munzinger J Gaucherel C Curt T Heacutely C (2013c) Inferringsavannah-rainforest boundary dynamics from vegetation structure andcomposition a case study in New Caledonia Australian Journal ofBotany 61 128ndash138 doi101071BT12255

Jackson JF Adams DC Jackson UB (1999) Allometry of constitutivedefense a model and a comparative test with tree bark and fire regimeAmerican Naturalist 153 614ndash632 doi101086303201

Jaffreacute T Bouchet P Veillon JM (1998a) Threatened plants of NewCaledonia is the system of protected areas adequate Biodiversity andConservation 7 109ndash135 doi101023A1008815930865

Jaffre T Rigault F Dagostini G (1998b) Impact des feux de brousse surles maquis ligno-herbaceacutes des roches ultramafiques de Nouvelle-Caleacutedonie Adansonia 20 173ndash189

Lawes MJ Midgley JJ Clarke PJ (2013) Costs and benefits of relative barkthickness in relation to fire damage a savannaforest contrast Journalof Ecology 101 517ndash524 doi1011111365-274512035

Marimon BS Felfili JM Fagg CW Marimon-Junior BH Umetsu RKOliveira-Santos C Morandi PS Lima HS Terra Nascimento AR(2012) Monodominance in a forest of Brosimum rubescens Taub(Moraceae) structure and dynamics of natural regeneration ActaOecologica 43 134ndash139 doi101016jactao201207001

320 Australian Journal of Botany T Ibanez and P Birnbaum

exampleC albicans has relatively thick bark and its investmentin bark thickness is disproportionally higher when the trees aresmall (Ibanez et al 2013b) enhancing its probability ofestablishment in fire-prone ecosystems (see Jackson et al1999 Lawes et al 2013) Furthermore all Codia species arelikely to be able to resprout after fire enhancing the probabilityof persistence in fire-prone ecosystems (Gignoux et al 1997Higgins et al 2000) Resprouting has been observed forC discolour and C nitida in maquis (Jaffre et al 1998b) andfor C albicans and C montana in savannas (Ibanez 2012) CMis also possibly pre-adapted to poor-nutrient soils giving it acompetitive advantage (Pillon et al 2009)

Conclusions

The monodominance of CM is clearly an early and non-persistent step in the secondary succession from savanna tomixed rainforest Given our state of knowledge it is difficult toidentify which combination of traits and environmental conditionslead to the monodominance of CM Monodominance in earlysuccession often results from a disturbance such as fire and thepresence of a species well adapted to and able to rapidly occupythe disturbed environment It is crucial to understand suchvegetation dynamics in order to effectively manage these areasHere rather than preventing recovery CM likely allowed aquick closure of anthropogenic savannas followed by a slowrecovery of diversity toward a mixed rainforest Moststudies have focussed on the ecosystem lsquoconsequencesrsquo ofmonodominant forest (eg Torti et al 2001 Brookshire andThomas 2013) but species such as CM that are able to rapidlyoccupy a disturbed environment and even form monodominantforest may provide ecosystem lsquobenefitsrsquo for example by limitingsoil erosion and maintaining soil quality

Acknowledgements

This work was funded by the Southern Province of New Caledonia(C 315-12) We thank the personnel of the provincial park Parc desGrands Fougegraveres for their hospitality and logistical support as well as thestaff of Noumeacutearsquos herbarium of IRD We are grateful to Juliane KaohGendrilla Warimavute Paul Birmbaum and Michegravele Magat for help withfieldwork andCeacutelineChambreyVanessaHequet andHerveacuteVandrot for plantidentification We thank Jennifer Read Tanguy Jaffreacute Lynda Prior as well astwo anonymous reviewers for their valuable comments on the manuscript

References

Brookshire ENJ Thomas SA (2013) Ecosystem consequences of treemonodominance for nitrogen cycling in lowland tropical forest PLoSONE 8 1ndash7

Chatain A Read J Jaffre T (2009) Does leaf-level nutrient-use efficiencyexplain Nothofagus-dominance of some tropical rain forests in NewCaledonia Plant Ecology 201 51ndash66 doi101007s11258-008-9477-z

Connell JH Lowman MD (1989) Low-diversity tropical rain forests ndash somepossible mechanisms for their existence American Naturalist 13488ndash119 doi101086284967

DegagneRSHenkel TW Steinberg SJ Fox Iii L (2009) IdentifyingDicymbecorymbosa monodominant forests in Guyana using satellite imageryBiotropica 41 7ndash15 doi101111j1744-7429200800446x

Fonty E Molino J-F Prevost M-F Sabatier D (2011) A new case ofneotropical monodominant forest Spirotropis longifolia

(LeguminosaendashPapilionoideae) in French Guiana Journal of TropicalEcology 27 641ndash644 doi101017S0266467411000356

Gignoux J Clobert J Menaut JC (1997) Alternative fire resistancestrategies in savanna trees Oecologia 110 576ndash583doi101007s004420050198

Greene DF Johnson EA (1989) A model of wind dispersal of winged orplumed seeds Ecology 70 339ndash347 doi1023071937538

Hart TB (1990) Monospecific dominance in tropical rain forests Trends inEcology amp Evolution 5 6ndash11 doi1010160169-5347(90)90005-X

Hart TB Hart JA Murphy PG (1989) Monodominant and species-richforests of the humid tropics causes for their co-occurrence AmericanNaturalist 133 613ndash633 doi101086284941

Henkel TW (2003) Monodominance in the ectomycorrhizal Dicymbecorymbosa (Caesalpiniaceae) from Guyana Journal of TropicalEcology 19 417ndash437 doi101017S0266467403003468

Higgins SI Bond WJ Trollope WSW (2000) Fire resprouting andvariability a recipe for grass-tree coexistence in savanna Journal ofEcology 88 213ndash229 doi101046j1365-2745200000435x

Hopkins HCF (2005) Nomenclature and typification in the endemic genusCodia (Cunoniaceae) from New Caledonia Adansonia 27 243ndash254

Hopkins HCF Fogliani B Pillon Y (2007) Four new species in the endemicgenus Codia (Cunoniaceae) from New Caledonia Kew Bulletin 62259ndash274

Ibanez T (2012) lsquoDynamique des forecircts denses humides et des savanes enreacuteponse aux incendies en Nouvelle-Caleacutedoniersquo Rainforest and savannadynamics in response to fires in New Caledonia (Universiteacute Aix-Marseille Aix en Provence France)

Ibanez T Heacutely C Curt T Gaucherel C (2012) Sharp transitions ofmicroclimatic conditions between savanna and forest in NewCaledonia insights into vulnerability of forest edges to fire AustralEcology doi101111aec12015

Ibanez T Borgniet L Mangeas M Gaucherel C Geacuteraux H Heacutely C (2013a)Rainforest and savanna landscape dynamics in New Caledonia towardsa mosaic of stable rainforest and savanna states Austral Ecology 3833ndash45 doi101111j1442-9993201202369x

Ibanez T Curt T Heacutely C (2013b) Low tolerance of New Caledoniansecondary forest species to savanna fires Journal of VegetationScience 24 177ndash188 doi101111j1654-1103201201448x

Ibanez TMunzinger J Dagostini G Hequet V Rigault F Jaffreacute T BirnbaumP (2014) Structural and floristic diversity of mixed tropical rain forest inNew Caledonia new data from the New Caledonian Plant Inventoryand Permanent Plot Network (NC-PIPPN) Applied Vegetation Science17 386ndash397

Ibanez T Munzinger J Gaucherel C Curt T Heacutely C (2013c) Inferringsavannah-rainforest boundary dynamics from vegetation structure andcomposition a case study in New Caledonia Australian Journal ofBotany 61 128ndash138 doi101071BT12255

Jackson JF Adams DC Jackson UB (1999) Allometry of constitutivedefense a model and a comparative test with tree bark and fire regimeAmerican Naturalist 153 614ndash632 doi101086303201

Jaffreacute T Bouchet P Veillon JM (1998a) Threatened plants of NewCaledonia is the system of protected areas adequate Biodiversity andConservation 7 109ndash135 doi101023A1008815930865

Jaffre T Rigault F Dagostini G (1998b) Impact des feux de brousse surles maquis ligno-herbaceacutes des roches ultramafiques de Nouvelle-Caleacutedonie Adansonia 20 173ndash189

Lawes MJ Midgley JJ Clarke PJ (2013) Costs and benefits of relative barkthickness in relation to fire damage a savannaforest contrast Journalof Ecology 101 517ndash524 doi1011111365-274512035

Marimon BS Felfili JM Fagg CW Marimon-Junior BH Umetsu RKOliveira-Santos C Morandi PS Lima HS Terra Nascimento AR(2012) Monodominance in a forest of Brosimum rubescens Taub(Moraceae) structure and dynamics of natural regeneration ActaOecologica 43 134ndash139 doi101016jactao201207001

320 Australian Journal of Botany T Ibanez and P Birnbaum

McCoy S Jaffreacute T Rigault F Ash JE (1999) Fire and succession in theultramafic maquis of New Caledonia Journal of Biogeography 26579ndash594 doi101046j1365-2699199900309x

METEO-FRANCE (2007) lsquoAtlas climatique de la Nouvelle CaleacutedonieMETEO-France en Nouvelle Caleacutedoniersquo (METEO-France Noumeacutea)

MittermeierRARoblesGil PHoffmannMPilgrim J BrooksTMittermeierCG Lamoureux J da Fonseca GAB (2004) lsquoHotspots revisitedrsquo(Chicago University Press Chicago IL)

MoratP JaffreTTronchetFMunzinger J PillonYVeillon JMChalopinMBirnbaum P Rigault F Dagostini G Tinel J Lowry PPII (2012) Thetaxonomic reference base lsquoFloricalrsquo and characteristics of the nativevascular flora of New Caledonia Adansonia 34 179ndash221doi105252a2012n2a1

Muller-Landau HC Wright SJ Calderon O Condit R Hubbell SP (2008)Interspecific variation in primary seed dispersal in a tropical forestJournal of Ecology 96 653ndash667doi101111j1365-2745200801399x

Myers N (1988) Threatened biotas lsquohot spotsrsquo in tropical forests TheEnvironmentalist 8 187ndash208 doi101007BF02240252

Nascimento MT Proctor J (1997) Soil and plant changes across amonodominant rain forest boundary on Maraca Island RoraimaBrazil Global Ecology and Biogeography Letters 6 387ndash395doi1023072997339

Nathan R Safriel UN Noy-Meir I (2001) Field validation and sensitivityanalysis of a mechanistic model for tree seed dispersal by wind Ecology82 374ndash388doi1018900012-9658(2001)082[0374FVASAO]20CO2

Newbery DM Alexander IJ Rother JA (2000) Does proximity toconspecific adults influence the establishment of ectomycorrhizal treesin rain forest New Phytologist 147 401ndash409doi101046j1469-8137200000698x

Newbery DM van der Burgt XM Worbes M Chuyong GB (2013)Transient dominance in a central African rain forest EcologicalMonographs 83 339ndash382 doi10189012-16991

Oksanen J Blanchet FG Kindt R Legendre P Minchin PR OrsquoHara RBSimpson GL Solymos P Stevens MHH Wagner H (2012) lsquovegancommunity ecology packagersquo Available at httpcranr-projectorgwebpackagesveganindexhtml [Accessed 05 July 2014]

Peh KSH Lewis SL Lloyd J (2011) Mechanisms of monodominancein diverse tropical tree-dominated systems Journal of Ecology 99891ndash898 doi101111j1365-2745201101827x

Pillon Y Munzinger J Amir H Hopkins HCF Chase MW (2009) Reticulateevolution on a mosaic of soils diversification of the New Caledonianendemic genusCodia (Cunoniaceae)MolecularEcology18 2263ndash2275doi101111j1365-294X200904178x

QGIS Development Team (2013) lsquoQGIS geographic information systemrsquo(Open Source Geospatial Foundation) Available at httpqgisosgeoorg[Accessed 5 July 2014]

R Core Team (2012) lsquoR a language and environment for statisticalcomputingrsquo (R Foundation for Statistical Computing Vienna)

Read J Jaffre T (2013) Population dynamics of canopy trees in NewCaledonian rain forests are monodominant Nothofagus (Nothofagaceae)forests successional to mixed rain forests Journal of Tropical Ecology29 485ndash499 doi101017S0266467413000576

Read J Hallam P Cherrier JF (1995) The anomaly of monodominanttropical rain-forests ndash some preliminary-observations in theNothophagus-dominated rain-forests of New-Caledonia Journal ofTropical Ecology 11 359ndash389 doi101017S026646740000883X

Read J Jaffre T Godrie E Hope GS Veillon JM (2000) Structural andfloristic characteristics of some monodominant and adjacent mixedrainforests in New Caledonia Journal of Biogeography 27 233ndash250doi101046j1365-2699200000407x

Read J Jaffre T Ferris JM McCoy S Hope GS (2006) Does soil determinethe boundaries of monodominant rain forest with adjacent mixed rainforest and maquis on ultramafic soils in New Caledonia Journal ofBiogeography 33 1055ndash1065 doi101111j1365-2699200601470x

Rigg LS Enright NJ Jaffre T Perry GLW (2010) Contrasting populationdynamics of the endemic NewCaledonian conifer Araucaria laubenfelsiiin maquis and rain forest Biotropica 42 479ndash487doi101111j1744-7429200900615x

Serbesoff-King K (2003) Melaleuca in Florida a literature review on thetaxonomy distribution biology ecology economic importance andcontrol measures Journal of Aquatic Plant Management 41 98ndash112

Torti SD Coley PD Kursar TA (2001) Causes and consequences ofmonodominance in tropical lowland forests American Naturalist 157141ndash153 doi101086318629

Monodominance at the rainforest edge Australian Journal of Botany 321

wwwpublishcsiroaujournalsajb