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Edaphic and Human Effects on Landscape-Scale Distributions of Tropical Rain Forest Palms

Author(s): Deborah A. Clark, David B. Clark, Rosa Sandoval M., Marco Vinicio Castro C.Source: Ecology, Vol. 76, No. 8 (Dec., 1995), pp. 2581-2594Published by: Ecological Society of AmericaStable URL: http://www.jstor.org/stable/2265829

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Ecology, 76(8), 1995, pp. 2581-2594? 1995 by the Ecological Society of America

EDAPHIC AND HUMAN EFFECTS ON LANDSCAPE-SCALEDISTRIBUTIONS OFTROPICAL RAIN FOREST PALMS1DEBORAH A. CLARK,2 DAVID B. CLARK,2 ROSA SANDOVAL M., AND

MARCO VINICIO CASTRO C.3Organization for Tropical Studies, La Selva Biological Station,INTERLINK-341, P.O. Box 02-5635, Miami, Florida 33152 USAAbstract. We studied the landscape-level spatial variation in distribution and abun-dance of seven species of canopy and subcanopy palms in a neotropical rain forest. Within568 ha of nonswamp old-growth lowland forest at the La Selva Biological Station, CostaRica, we sampled at 516 intersections of a reserve-wide grid to systematically assess thespecies' distributions across the major edaphic gradients. We found mosaics of communitystructure related to marked within-forest variability in both soil and topography. Total stem

density of this guild varied with both edaphic factors. Steep sites had twice as many largepalms (> 10 m tall) per hectare than those on gentler topography or at lower slope positions.The combined density of subcanopy and canopy palms also varied significantly among soiltypes in the smallest size class (1-5 m tall), but not for larger individuals. Local (point)species richness of the subcanopy and canopy palms varied among soil types.Of the seven species, two (Astrocaryum alatum and A. confertum) were rare. All othersshowed significant edaphic variation in their distribution and/or estimated density. Twoclosely related species had strong and opposite edaphic associations. Euterpe macrospadixwas biased toward steep topography and less fertile sites. Prestoea decurrens was nearlyommipresent on soil types with gentle topography while absent from half the points onsoils with steep slopes. Two other closely related species, Iriartea deltoidea and Socrateaexorrhiza, while virtually omnipresent across soil types and topographic positions, showedmarked reciprocal variation in density between related soils. Iriartea's spatial distributionfurther indicates local removal of this species from one sector of the old growth by humanharvesting (with subsequent apparent "release" of Socratea in this site). The most abundantspecies, Welfia georgii, while present at all sample points, showed significant among-soilvariation in density.This substructuring of the arborescent palm guild results from the interplay of edaphicvariation and past human activity. These findings and evidence from other sites suggestthat marked spatial heterogeneity in community structure, at small to large scales (0.5-103ha), may be general among tropical wet forests. Study of the spatial scales and causes ofthis variability will produce a more robust understanding of these complex ecosystems.Key words: Astrocaryum; Costa Rica; edaphic variation; Euterpe; Iriartea; landscape ecology;palms; Prestoea; Socratea; spatial heterogeneity; tropical rain forest; Welfia.

INTRODUCTIONTo understand many aspects of populations, com-munities, and ecosystems, a first need is to determinehow the distributions and abundances of the organismsvary across the landscape. To develop predictive powerfurther requires understanding the processes, past andpresent, underlying the spatial heterogeneity thus iden-

tified (Levin 1992). Although these ideas are generallyrecognized by most ecologists, current ecological stud-

ies often lack the underpinnings of a clear understand-ing of the important scales of spatial variation withinstudy sites.In the wet tropics a growing number of studies atsmall-to-large scales within old-growth forest havedemonstrated strong effects of edaphic heterogeneityon floristic composition (Ashton 1969, Newbery andProctor 1984 and cited references, Lescure and Boulet1985, Lieberman et al. 1985, Basnet 1992, Johnston1992, Ruokolainen and Tuomisto 1993, Gentry and Or-tiz 1993, Oliveira-Filho et al. 1994). Much of the Am-azon Basin is a highly interdigitated mosaic of foresttypes produced by the erosion/deposition cycles of themajor rivers (Salo and Rasanen 1989, Foster 1990) andmarked variation in terrafirme parent material and geo-chemistry (Jordan 1985, Chauvel et al. 1987, Guillau-met 1987). Another potential source of small-to-me-dium scale spatial heterogeneity within tropical wet

I Manuscript received 12 September 1994; revised 21 Feb-ruary 1995; accepted 4 March 1995; final version received27 March 1995.2 Present institutional address: Department of Biology, Uni-versity of Missouri-St. Louis, 8001 Natural Bridge Road, St.Louis, Missouri 63121 USA (mailing address remains asabove).I Present address: Instituto Nacional de Biodiversidad, San-to Domingo de Heredia, Costa Rica.


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2582 DEBORAH A. CLARK ET AL. Ecology, Vol. 76, No. 8TABLE 1. The seven species of canopy and subcanopy palms (Arecaceae, Subfamily Arecoideae) in old-growth forest atLa Selva and their local uses. Tribe designations are from Uhl and Dransfield (1987). Voucher specimens are from theCosta Rican National Herbarium. Local uses were determined by interviewing eight long-term residents of the surroundingregion (Cant6n de Sarapiquf) about recent historical uses of each palm species, which they identified from line drawings.

Tribe Species (voucher no.) Local usesIriarteeae Iriartea deltoidea Ruiz & Pav6n [Chac6n, heart-of-palm, construction woodChac6n, Mora 1968]Socratea exorrhiza (Martius) Wendl. [W. D. construction wood (less used than Iriartea),Stevens 24559] rarely heart-of-palmAreceae Prestoea decurrens (Wendl.) H. E. Moore [M. noneH. Grayum, C. Jermy 6783]Euterpe macrospadix Oersted [M. H. Grayum heart-of-palm (less used than Iriartea)7813]Cocoeae Astrocaryum confertum Wendl. ex Burret [G. nonede Nevers, B. E. Hammel 7820]Astrocaryum alatum Loomis [W. D. Stevens none24625]Geonomeae Welfia georgii Wendl. ex Burret [M. Wei- thatchingmann & P. M. Rich 137]

forests is the historical or current impact of local humanactivity, from silviculture to selective harvesting, evenwithin stands considered to be old-growth (Gordon1982, Gomez-Pompa and Kaus 1990, Anderson 1990,Bush and Colinvaux 1994).

Understanding the patterns and causes of spatialvariability in the community structure of tropical wetforests can contribute to the resolution of importantquestions about these ecosystems. Is small-to-mediumscale edaphic heterogeneity more characteristic ofthese forests than of temperate stands? Could this bea factor in the maintenance of high species richness intropical rain forests? Are wet tropical forests charac-terized by major internal spatial heterogeneity in eco-system-level processes such as primary productivity?Is variability in site conditions and forest communitieslikely to have major impacts for efforts in tropical for-est conservation and restoration?Our goal in this study was to assess landscape-scalespatial heterogeneity within an old-growth neotropicalrain forest, as reflected in the distribution and abun-dance patterns of the large palms. An unprecedentedset of research tools for landscape-level studies of trop-ical rain forest (a reserve-wide grid system, soil map,and Geographical Information System [GIS]) is newlyavailable at the study site. We used them to ask thefollowing questions, at the scale of 500 ha of contig-uous forest: (1) How do the abundance, size distribu-tion, and local species diversity of the guild of sub-canopy and canopy palms vary with respect to the land-scape-scale variation in soil and topography? (2) Dothe distribution and abundance of the individual speciesvary with edaphic conditions, and do these patternsdiffer among species? (3) Is there evidence of humanimpact on the distributions of large palms in the old-growth forest?

STUDY SITE AND SPECIESThe La Selva Biological Station of the Organizationfor Tropical Studies (OTS) is a 1550-ha reserve in the

Atlantic lowlands of Costa Rica (10?26' N, 84?00' W;elevation 37-150 m). It is classified in the Holdridgelife zone system as tropical wet forest (Hartshorn andHammel 1994). Mean annual rainfall is 3962 mm, withevery month averaging at least 100 mm of rain (Sanfordet al. 1994).The flora includes 323 tree species (Hartshorn andHammel 1994) and is rich in palms (31 native species,Chazdon 1985; 25% of all woody stems ?10 cm indiameter, Lieberman et al. 1985). Although not subjectto large-scale disturbances such as hurricanes, the for-est is very dynamic. Stem turnover is high (2.0-2.3%/yr for trees ?10 cm dbh; Lieberman et al. 1990), as isthe frequency of gap formation (Hartshorn 1978, San-ford et al. 1986).La Selva's soils range from relatively fertile entisolsand inceptisols to infertile ultisols (Sollins et al. 1994).The 1:10 000 soils map of La Selva (Sancho and Mata1987) demarcates 23 consociations (mapping unitswithin which ?75% of the area is the described soiltype) and one complex.Our study species are the seven subcanopy to canopypalms found in old-growth at La Selva (Table 1).Henceforth all except the Astrocaryum species are des-ignated by genus name only. Four species have beenlocally harvested (for heart-of-palm, constructionwood, thatching) in recent history (Table 1).

METHODSTo evaluate landscape-scale distributions of the large

palms in upland old-growth forest, we used the originalLa Selva reserve ("Original La Selva"; McDade andHartshorn 1994), after excluding swamp, secondaryforest, disturbed habitats, and the 12.4 ha of restrictedaccess plots. Within the resulting study area (568 ha;Fig. 1) we sampled at intersections of La Selva's re-serve-wide grid (posts every 50 m along lines at 100-m intervals; accuracy ?20 cm). In the limited areas ofalluvial soils, we sampled at all grid intersections (N= 78). On the nonalluvial soils we sampled at the in-


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December1995 TROPICALPALM COMMUNITYSTRUCTURE 2583tersections along every other grid line (thus along linesseparated by 200 m; N = 438 grid points). We excludedpoints that fell within streams or floodable micrositesas well as those 30()m from secondary forest or alteredhabitat.

Pailnm amnplinig.-From data at each sample point(grid post) we evaluated distributions of the seven palmspecies in two ways: in terms of estimated density andpresence/absence.

1. Estimnated ensitv.-For each of four size classes,we measured the distance from each sample point tothe nearest individual of any of the species and notedthe species of that palm. This "Closest IndividualMethod" (Cottam and Curtis 1956) enables estimationof stem density [Densitv (N/ha) = 10 000/(4D2)J, whereD is the mean distance in metres to the closest indi-vidual (the mean of the distances of Closest Individualsfrom all sample points). At each point we used thistechnique tor each of four size classes: 1-5, >5-10,> 10(-15, and > 15 m tall. A telescoping 15--mmeasur-ing pole was used to evaluate palm heights. For eachsize class, density of each species in a given area (i.e.,in a given soil type or at a given topographic position)was calculated by multiplying the total stem density ofcanopy and subcanopy palm species (see formulaabove), by the proportion of that species among theClosest Individuals sampled in the area.2. Preseele/Absence.-For each of the seven studyspecies we noted whether any individual > 1 m tall wasvisible (at any distance) in any direction from the gridpost or while measuring the Closest Individuals.Edaiphicfactors: Soils.-The La Selva soils map isin the station's GIS (Arc/Info 6.0.1, on Sun Sparc IIworkstations). We used our field notes regardingstreams, swamps, and topography to refine this map,and then grouped related soil map units into four cat-egories. The resulting GIS coverage was used to clas-sify each sample point by major soil type.Alluvium is an Andic Humitropept (Inceptisol) ongently undulating terrain. Although divided into theExperinental and Holdridge consociations, which werepreviously considered distinct terraces (Sollins et al.1994), the grid survey data (OTS records) show thesesectors to be at equivalent elevations (Experimental:mode = 42-44 m, N = 132; Holdridge: mode = 42-44 m, N = 398). While low in pH and exchangeablebases, they have higher pH, extractable phosphorus (P),and/or exchangeable bases than the other three soiltypes (Sollins et al. 1994; J. S. Denslow and G. Chav-erri, unpublished data).Arboleda is a consociation thought to represent old,highly weathered alluvial deposits that overlie verybroken terrain (Sollins et al. 1994). This soil appearsintermediate between the Alluvium (Holdridge con-sociation) and Residual soils in extractable P,but equiv-alent in pH to the Residual soils (J. S. Denslow andG. Chaverri. unlpublished data)The Residual consociations (Jagutar, Matabttey, and

4 S @04.

N

4 1~~~~~0p'4 1

0 100 300 800 metresMVCC-JJP/Jan95

Ftc;.1. The studyareain old-growth(nonswamnp)orest(thethick blackborder ndicates heboundaryof thesampledarea).Circles denote the 516 pointssampledalongthe 50 x200 m grid coveringLa Selva. Differentgrey tones indicatethe four soil types (from lightest to darkestgrey tone: Al-luvium [Holdridgeand ExperimentalConsociationsof theAlluvium are labeled as "Ho" and "Ex' l; Arboledasoil,Residualsoil; Streamisoil [swampsare indicatedby the fig-uredhatchingpattern]).Trailsare shown as dashed ines.Thedistributionof Iri(artea leltoidleats shown by: present (0);absent(0).

Esquina) are highly weathered soils derived from oldlava flows and overlie broken ridge-valley topography.They are acidic and low in exchangeable bases andextractable P (Sollins et al. 1994; J. S. Denslow andG. Chaverri, un;ipublishledaita). The Jaguar and Mai-tabuievconsociations, classified as Ultisols (Typic Tro-pohumults), cover 45% of La Selva (Sollins et al.1994).The Stream consociations occur in the valley bot-toms of principal streams: El Scalto(Lithic Humitro-pept), El Surd-Saltito (Typic Humitropept), and El Ta-conazo (Typic Tropaquept). All are strongly acidic,very low in exchangeable bases, and with poor-to-mod-erate drainage (Sollins et al. 1994).Edap)hicfactors: To)pograiphvy.-In the field we cat-egorized each sampling point (grid post) by topograph-ic position: Slope Crest (just above to just below theupper breakpoint of a slope); Steep Slope, ModerateSlope, Gentle Slope (all the slope positions betweenCrest and Base, with slopes classed by relative steep-


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2584 DEBORAH A. CLARK ET AL. Ecology, Vol. 76, No. 8550500- IEI RESIDUAL111ARBOLEDAcu 450- sZZ STREAMS

o400- l ALLUVIUM1350 15300-zii 250-200-

C< 150-100-

501m > 5-lOin >10-15m >15m

HEIGHTSIZE CLASSFIG. 2. Variation in total palm density (all seven species

combined) by size class and soil type. Sample sizes are givenin Table 2. Probabilities are for a Kruskal-Wallis test of thedistances to the Closest Individual (see Methods), y soil type.* P ' 0.05.

ness); Base of Slope (just above to just below the lowerslope breakpoint); and Flat (flat terrain, whether onbroad ridges or terraces or in swales). When this fieldindex was combined with slope angle measurement atthe same point in another La Selva study (D. B. Clarket al., unpublished data), mean slope angles were (N,points): Steep Slope, 24.70 (91); Moderate Slope, 15.70(124); Gentle Slope, 6.60 (150); and Flat, 1.60 (60).Statistical analysis.-To test for species associationswith edaphic conditions, the presence-absence datawere tested with chi-square (number of sample pointswith a given species present and absent vs. soil typesor topographic positions). To test whether total palmdensity in a given size class differed among soil types(or topographic positions), a Kruskal-Wallis test wasperformed on the Closest Individual distances for thatsize class in each soil type (or topographic position);significantly different distances to Closest Individualsindicate significant density differences among theedaphic conditions (greater distances indicate lowerdensity). When total palm densities did not differ acrosssoils, species could be individually tested for an as-sociation between their density and soil. A chi-squaretest was used to compare the soil types in terms of theClosest Individuals that were and were not the speciesin question. Significant among-soil variation in a spe-cies' representation among Closest Individuals indi-cates that the species' density varies significantlyamong soils. Throughout, the probability used for sig-nificance is 0.05.

RESULTSTotal palm densityThe abundance of subcanopy and canopy palms var-ies greatly across the La Selva landscape. Changes in

total estimated density across topographic and soil gra-dients produce marked spatial heterogeneity in theirlocal abundance.Density and palm size.-By far the highest estimateddensities (203-509 palms/ha, the seven species com-

bined) occurred in the smallest size class (1-5 m tall;Fig. 2). Abundance dropped sharply at larger sizes.Topographic effects.-Estimated stem density variedsignificantly in relation to topography. In the two largersize classes (>10-15 m tall, >15 m tall), total densitydecreased continuously from slope crests, to slopes ofdecreasing steepness, to slope bases and flat terrain(Fig. 3B). In both size classes palm density varied two-fold among topographic positions. The number ofsmaller palms per hectare, however, did not vary sig-nificantly with topography (Fig. 3A).

-: 4000

630-zLU 200-J

0-iS5m >5-lOinm

60B. *

50-o 40

CO 30z20-

-J-

0>10-15 m >15 m

HEIGHTSIZE CLASSFIG. 3. The relation of total palm density (all seven spe-cies combined) to topographic position (all soils combined).(A) Individuals in the two smaller size classes. (B) The twolarger size classes (note different y axis). Probabilities are fora Kruskal-Wallis test of the distances to the Closest Individ-ual (see Methods),by topographic position. Fill patterns, fromleft to right (with N, points sampled): slope crest-138; steepslope-105; moderate slope-42; gentle slope-91; slopebase-57; flat-83. ** P ' 0.01; *** P ' 0.001.


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December 1995 TROPICAL PALM COMMUNITY STRUCTURE 2585

100- RESIDUAL900 l_ARBOLEDAH w 5 _ V/A STREAMSz 80 E ALLUVIUMwC/)

W 70 -CE0~~~~~~~~~~~~~~~~~~~~~~~~~~RW 60-w 50 1

;'-0l l

00 2010

WE SO IR EU PR AL COSPECIES

FIG. 4. The distribution of the seven canopy and subcanopy palm species with respect to the four major soil classes.Data for each species are the percent of sample points in each soil type at which any individual >1 m tall was observed.Sample sizes as in Table 2. Species abbreviations: WE-Welfia, SO-Socratea, IR-Iriartea, EU-Euterpe, PR-Prestoea,AL-Astrocaryum alatum, CO-Astrocaryum confertum.

Soil effects.-The relation between estimated palmdensity (all seven species combined) and soil type (Fig.2) contrasted with the topographic patterns. For thethree larger size classes, palm densities were equivalentacross the four soil types. Abundance of the smallestpalms, however, did vary significantly among soils(Kruskal-Wallis, P < 0.03). Stem density at this sizewas much lower on the Streams soils than on the otherthree soil types (Tukey a posteriori pairwise compar-ison, P < 0.05).

Species distributionsThe seven palm species have different distributionpatterns across La Selva. The combined data on pres-ence/absence and estimated density reveal: (1) general

rarity of the two Astrocaryum species; (2) strong andopposite associations with soil type and topography forthe species Euterpe and Prestoea; (3) evidence of localremoval of one species (Iriartea) through human har-vesting; (4) reciprocal density differences between Ir-iartea and Socratea; and (5) significant intersoil vari-ation in the density of one ubiquitous species (Welfia).Astrocaryum.-Both Astrocaryum species were rarein the sampled area (Fig. 4). In all four soil types, theyoccurred at few sample points (3-5%, A. confertum;2-i 1%, A. alatum). The estimated density of A. con-fertum (from Closest Individual data) was 0.0 stems/ha in all size classes on all soils, except for the 1-5 mheight class on Residual soils (1.2 stems/ha). Similarly,A. alatum estimated density was 0.0-3.0 stems/haacross sizes and soils. This species, however, is abun-dant in swamps at La Selva; Hartshorn(1983) reported

30.5 stems/ha (?10 cm diameter) in a 2-ha plot inswamp.Euterpe.-The presence/absence data (Fig. 4) re-vealed strong soil-related heterogeneity in Euterpe'sdistribution (chi-square, df = 3, P < 0.0001). Althoughpresent at 91% of sample points in the Residual soils,this species occurred at only 10% of the points in Al-luvium, with intermediate frequencies in the other twosoil types. A parallel pattern is seen with the ClosestIndividual data (percent of sample points with Euterpeas ?1 of the four Closest Individuals: Residual, 38%;Arboleda, 21%; Streams, 25%; Alluvium, 1%; chi-square, df = 3, P < 0.0001).Euterpe's abundance also significantly varied withsoil type at all sizes (Appendix). Estimated densities

were markedly higher on the Residual soils than on theother three soils. A single individual occurred in thedensity sampling on the Alluvium.Because topography varies with soil type (Table 2),a species' association with soil type could reflect re-sponses either to topography and/or to substrate per se.To separate these factors, we carried out two additionalanalyses of Euterpe's distribution patterns. The manysample points on the Residual soils allow assessmentof species' topographic associations within a single soiltype. Euterpe's presence/absence patterns within theResidual soils (Fig. SA) strongly varied with topo-graphic position. While present at >90% of points as-sociated with steeper topography (Slope Crest, SteepSlope, Moderate Slope), Euterpe was absent from halfof the Flat sites. Its distribution was also strongly as-sociated with soil type per se. Comparing presence/


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2586 DEBORAH A. CLARK ET AL. Ecology, Vol. 76, No. 8TABLE 2. Topographic variation on the four major soil types(see Methods or descriptions of soil classes and topograph-ic positions). Data are the proportion of sample points ineach topographic position, within each soil type.

Topographic Proportion within each soil typeposition Residual Arboleda Stream AlluvialSlope crest 0.30 0.36 0.00 0.31Steep slope 0.21 0.25 0.00 0.03Moderate slope 0.27 0.11 0.00 0.13Gentle slope 0.09 0.05 0.15 0.19Base of slope 0.10 0.21 0.69 0.06Flat 0.03 0.02 0.15 0.28

Total 1.00 1.00 1.00 1.00N 329 44 65 78Area sampled(ha)* 340 43 65 64

* Additional area was sampled at upland sites embeddedwithin the 55 ha of swamp in the total study area; such within-swamp points were classified to soil type based on the localtopography and proximity to soil map units.

absence at the same topographic position (the four po-sitions with adequate samples) showed much more fre-quent occurrence on the Residual soils than on the Al-luvium (Fig. 6A).Together these patterns suggest balanced avoidanceof gentle topography (Table 2) and more fertile con-ditions (based on the limited nutrient data for La Selvasoils; see Methods). Euterpe's distribution was: nearlyomnipresent on Residual soils (steep topography, in-

fertile); intermediate occurrence on both the Arboledasoils (steep topography, intermediate fertility) and theStreams soils (base of slopes/flat terrain, infertile); andnearly absent from Alluvial soils (gentle topography,fertile). Euterpe's significant density differences amongsoils (Appendix) paralleled these presence/absence pat-terns.Prestoea.-This close relative of Euterpe was alsostrongly associated with both topographic and soil vari-ation, but in directions opposite to those found withEuterpe. Prestoea's presence/absence patterns (Fig. 4)varied markedly among soil types (chi-square, df = 3,

P < 0.0001). While at only 48-53% of points in theResidual and Arboleda soils, it occurred at 91-92% ofpoints in the Streams and Alluvial soils. A similar pat-tern exists in the percent of sample points with Prestoeaas any of the four Closest Individuals (Residual, 14.3%;Arboleda, 20.5%; Streams, 52.3%; Alluvium, 46.2%;chi-square, df = 3, P < 0.0001).Prestoea's estimated density (stems per hectare; Ap-pendix) varied significantly across soil types in all threesize classes (smaller than the other six species, Pres-toea only occurred once as a Closest Neighbor at >15m height). Overall, Prestoea density was lowest on theResidual soils. The ratio between its density on theAlluvium and on the Residual soils increased with sizeclass, from 3.8 (1-5 m tall palms) and 3.5 (5-10 mtall) to 5.0 (10-15 m tall). Stronger shifts with increas-ing size class occurred in the ratios between Prestoea's

density on the Streams soils and Arboleda soils, andits density on the Residual soils (Density ratios, 1-5m, >5-10 m, and >10-15 m height classes, respec-tively: Streams/Residual-2.3, 3.8, 7.7; Arboleda/Re-sidual-0.9, 2.1, 5.0). These patterns suggest that inboth the 1-5 m and >5-10 m size classes, Prestoeasuffers higher mortality on the Residual soils than onthe Streams or Arboleda soils.

As with Euterpe, Prestoea's occurrence within theResidual soils (Fig. SA) was strongly associated withtopographic position, but in the opposite direction tothat of Euterpe. While present at only 29 and 47% ofpoints associated with steeper topography (Slope Crestand Steep Slopes, respectively), Prestoea was at 78 and81% of the Slope Base and Flat sites. Its distribution

100 A.H 90zww 70-wT- 50-ul) 40-z 30-

U_ 20-0-'0 10-0 EUTERPE PRESTOEA

100 BwUl) 80-wcEo~70-cE 60-

50- ftu) 40-Z0 30 qu_ 200S 10S}0 IRIARTEASOCRATEA WELFIA

FIG. 5. Topographic affinities of the abundant canopy/subcanopy palm species, controlling for soil type. Data arethe percent of sample points at which each species was presentat each topographic position, within the Residual soils. Fillpatterns, from left to right (with N, points): slope crest (98);steep slope (70); moderate slope (90); gentle slope (30); slopebase (32); flat (9). Probability (**** P ' 0.0001) is from achi-square test for association of species presence/absencewith topographic position. (A) Euterpe and Prestoea (df = 3for both chi-square tests; for each, two pairs of adjacent to-pographic positions were combined to eliminate expected val-ues


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was also significantly associated with soil type per se,in analyses controlling for topography (Fig. 6B). Incontrast to Euterpe (Fig. 6A), Prestoea occurred morefrequently on the Alluvium than on Residual soils atall four topographic positions that could be compared(chi-square, df = 1, P < 0.0001 and P = 0.01 for twoof four comparisons).Taken together, these patterns indicate that Pres-toea's distribution is associated with both soil and to-pography. A bias toward more fertile soil is suggestedby the Alluvium/Residual comparison at given topo-graphic positions (Fig. 6B) and by the size-related in-crease in relative density on the Arboleda soil, com-pared to the (less fertile, but topographically equiva-lent) Residual soils. The presence/absence data, how-ever, suggest a stronger association with topographythan with soil. Prestoea was nearly omnipresent on theStreams and Alluvium soils (both soils of low slopepositions/gentle topography, while contrasting in fer-tility). Similarly, the species occurred at only about halfthe sample points on the two soils on highly dissectedterrain (Residual, Arboleda; Fig. 4), in spite of thesesoils' apparent fertility difference. The significantamong-soil differences in Prestoea's stem density inthe two smaller size classes (Appendix) follow thesame general trend (markedly lower densities in theResidual and Arboleda soils than in the Streams andAlluvium soils). In the largest size class, although thepattern is less clear, Prestoea's density is lowest on thesteep Residual soils and highest on the flat Streamssoils.

Iriartea.-Unlike Euterpe and Prestoea, Iriartea didnot show an association with topography (Fig. 5B). Itspresence/absence patterns (Fig. 4), however, did differsignificantly among soils (chi-square, df = 3, P =0.0000). Iriartea was present at 91-98% of samplepoints on all soils but Alluvium, where it occurred at50% of the points.

Mapping (Fig. 1) revealed a strong spatial bias inIriartea's distribution within the Alluvium. Althoughfound at all 36 sample points in the Holdridge con-sociation of the Alluvium, the species was virtuallyabsent from the Experimental consociation (present atonly 2 of 42 points). The two consociations are bothclassified as Andic Humitropepts (Sollins et al. 1994),and have equivalent distributions of topographic po-sitions (chi-square, df = 3, P = 0.89) and elevations(see Methods).An edaphic explanation for Iriartea's distributionwithin the Alluvium is unlikely given: (1) the species'lack of variation with topography; (2) its virtual om-nipresence in all four soil types (within the Alluvium,omnipresent in the Holdridge consociation); (3) thatboth strongly edaphically varying species, Euterpe andPrestoea, had equal estimated densities on the two Al-luvium consociations (Appendix); and (4) the similar-ity of the two consociations. A nonedaphic factor dis-tinguishing the two soil map units, however, is location

A. *** ***100-

Ul) 80-70-

m 60UJ I50-cl 40-Z 30-a- 20O 10C-0

SLOPE MOD GENTLE FLATCREST SLOPE SLOPE

100F . Su

Ul) 80-70-

w 60-LU I50-U) 40-Z 30-0a- 20-ILO 100

SLOPE MOD. GENTLE FLATCREST SLOPE SLOPEFIG. 6. Soil affinities of (A) Euterpe and (B) Prestoea,controllingfor topographicposition (Residual soils: whitebars; Alluvium, black bars). Each probability s for a chi-squaretest for associationof the species' presence/absencewith soil type, at a fixedtopographicposition (** P < 0.01;*** P < 0.001; **** P < 0.0001). N, sample points (Residualsoils and Alluvium, respectively): slope crest, 98 and 24;moderateslope, 90 and 10; gentle slope, 30 and 15; flat, 9and 22.

with respect to human activity and access. The Exper-imental consociation lies between a former commercialcacao plantation (operative until the 1980s) and theformer housing for La Selva farm workers (abandonedin the early 1980s). In contrast, the old-growth areasof the Holdridge consociation, while not far from aneighboring cattle ranch, are relatively remote frommodern human habitation. Taken together, these linesof evidence indicate that Iriartea's absence from theExperimental consociation is due to intense past har-vesting of the species from this sector of the La Selvaold-growth forest. Iriartea's absence from this conso-ciation in all size classes >1 m tall suggests completelocal removal of large stems by harvesting, with thisprocess occurring over a protracted period. Such ac-


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2588 DEBORAH A. CLARK ET AL. Ecology, Vol. 76, No. 8TABLE 3. The relationship between the densities of Socratea exorrhiza (S) and Iriartea deltoidea (I) on related soil types.Probabilities are for chi-square tests of Closest Individual data; these tests effectively compare densities (see Methods) ofa given species on the two soils of each pair (or of the two species combined across the soil pair): *** P < 0.001; ** P< 0.01; * P < 0.05; NS, P > 0.05.

Density (stems/ha)Height class (m): 1-5 >5-10 >10-15 >15Soil I S (S + I) I S (S + I) I S (S + I) I S (S + I)

Alluvial consociationExperimental 0 58 (58) 0 11 (11) 1 16 (17) 0 23 (23)

NS NS NS ** ** NS * * NS * * NSHoldridge 47 35 (82) 13 0 (13) 13 4 (17) 10 5 (15)Arboleda 17 121 (138) 11 19 (30) 5 8 (13) 8 17 (25)

* * * * * NS NS NS NS NS NS NS * NS NSResidual 84 51 (135) 17 15 (32) 9 7 (16) 16 14 (30)

tivity could have been relatively recent, but is unlikelyto have occurred after strict site protection was estab-lished in the early 1980s.

Socratea.-As for Iriartea, the distribution of thisclosely related species was not associated with edaphicconditions. Within the Residual soils, Socratea's pres-ence/absence patterns did not vary with topographicposition (Fig. 5B). The species was present at 9 1-100%of the sample points in each of the four soil types (Fig.4). Nevertheless, Socratea's estimated density did varyamong soils (Appendix). In all four size classes, So-cratea's lowest density occurred on the Streams soils.In two of the four size classes, the among-soil densitydifferences were significant.Socratea and Iriartea have reciprocal density pat-terns on similar soils (Table 3). Between the Experi-mental and Holdridge consociations of the Alluvium,for example, both species showed significant densitydifferences in three of the four size classes. The inter-soil differences, however, are opposite for the two spe-cies. In spite of each species' large density differencesbetween consociations, the summed density of the twopalm species in each of these size classes is remarkablysimilar in the two consociations. None of the otherabundantpalm species (Euterpe, Prestoea, and Welfia)showed density differences between these two Alluvialconsociations (Appendix). Iriartea and Socratea alsoshowed reciprocal density patterns between the Resid-ual and Arboleda soils (Table 3). Between these twosoil types, which have similar topography (Table 2; chi-square, df = 4, P = 0.07), all seven palm species hadsimilar frequencies of occurrence (Fig. 4). In the 1-5m size class, however, Socratea and Iriartea had largesignificant differences in density between these soils,although the sum of the two species' densities in thissize class was remarkably similar between soils. In alleight comparisons for these two soil pairs (four sizeclasses, Experimental vs. Holdridge; four size classes,Arboleda vs. Residual), there is a reciprocal relation-ship between the densities of Iriartea and Socratea (onespecies' relatively higher density in the first soil com-pared to the second soil is complemented by the op-

posite pattern for the other species). The Binomialprobability of such an outcome is


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December 1995 TROPICAL PALM COMMUNITY STRUCTURE 2589Alluvium, 4.19 [Holdridge]. On no soil type were thereany sample points with fewer than two of the palmspecies present, however. Conversely, at no samplepoints in any soil did all the species co-occur.

DISCUSSIONEdaphic factors and forest heterogeneityThe variation in soil and topography within this old-growth forest has major impacts on the large palms: amesoscale (hundreds of hectares) gradient in local spe-

cies diversity; topographic changes in the group's over-all abundance; one species' absence from a major soiltype; and edaphic variation in density for many speciessize classes. All five common species showed markeddistributional and/or density changes over the edaphicgradients within La Selva.Palm species richness.-Over the landscape wefound highly significant variation in the local (point)species richness of subcanopy and canopy palms. Thelimited available soil data suggest that this diversitytrend is inversely related to soil fertility. The lowestlocal richness of palm species occurs in the Alluvium,the most fertile soil type (Sollins et al. 1994; J. S.Denslow and G. Chaverri, unpublished data). The soilswith highest local palm diversity, Streams and Resid-ual, appear to be the two least fertile (Sollins et al.1994; see Methods). Finally, the Arboleda soil, withintermediate local palm diversity, appears intermediate

in fertility between the Alluvium and Residual soils(see Methods). This trend is not confounded by stemdensity differences, which could produce spurious dif-ferences in species richness (palm densities were equiv-alent across soils in three of the four size classes; inthe 1-5 m size class, stem density was lowest in theStreams soil [Fig. 2], where local species richness washighest). Although the intersoil differences in local spe-cies diversity are clear, definitive analysis of their re-lation to soil fertility will await more systematic soilsampling.A negative correlation between tree species richnessand soil nutrients was found by Huston (1980) in a dataset from 46 forest plots distributed around Costa Rica.He attributed this pattern to lowered dominance by su-perior competitors in less productive sites. While verysuggestive, his findings involved possibly confoundingeffects from wide differences in elevation (which af-fects the species pool; Gentry 1982) and rainfall pat-terns. The patterns we found for the large palms at LaSelva, however, control for several factors that can varyamong geographically separated sites (e.g., climate, el-evation, species pool). They thus potentially provideinteresting support for Huston's hypothesis (contingenton confirmation by more extensive soil nutrient datafrom La Selva).Totalpalm density.-The abundance patterns of can-opy and subcanopy palms within the La Selva old-growth revealed marked topographic variation in this

tree guild. Estimated stem density of the two largersize classes varied twofold among topographic posi-tions, with highest densities on the slope crests andsteeper slopes.On steep slopes in La Selva old-growth forest heightis lower, and recent gaps (with canopy ?5 m high) arethree times more frequent than at other topographicpositions (D. B. Clark et al., unpublished data). Thedensity-topography variation of the larger size classesof palms may be due to the favoring of growth intothese sizes by more frequent gaps on steeper terrain.Topographic variation in tree stem density may befrequent in tropical wet forests. In a Central Amazonforest, Kahn and de Castro (1985) found substantiallyhigher palm densities on slope crests than at midslope,with lowest densities on the plateaus; they speculatedthat the higher densities at slope crests reflected greatergap formation on these more wind-prone sites. Simi-larly, in a Puerto Rican montane forest, Basnet (1992)found that the stem density of trees -10 cm dbh andof saplings 2.5-10 cm dbh decreased significantly fromridges to slopes to valley positions.In contrast, the soil variation at La Selva had littleimpact on the estimated density of canopy and sub-canopy palms. Only for the 1-5 m height class did totaldensity vary significantly among soils. For all othersize classes, the total density of stems in this speciesgroup was remarkably similar in the four soil types(Fig. 2), in spite of major intersoil variation in thedensity of individual species. This constancy in totalabundance of an internally varying species group sug-gests the operation of some sort of floristic "assemblyrules" with respect to the trees in this forest (cf. Gentryand Ortiz 1993). Although we as yet can propose nomechanisms that could produce such patterning, thispotentially important feature of tropical forests meritsstudy.

Species responses to edaphic variationThe patterns of local species richness of large palmsdemonstrated a high level of species mixing in this

guild. On all soils, the mean number of large palmspecies at each sample point was high (4.2-4.6 of sevenspecies). Nevertheless, all five abundant species variededaphically in density.Euterpe and Prestoea.-These closely related spe-cies showed marked associations with both soils andtopography (Euterpe with steep topography and lessfertile soils, Prestoea with gentle topography and morefertile soils). The limited additional data from La Selvasupport these patterns. Within three 4-ha forest inven-tory plots (one each on the Experimental and Holdridgeconsociations of the Alluvium and one on the Arboledasoil), Euterpe occurred at all the higher elevations (38-72 m) but was absent from the lowest elevations (32-36 m) (Lieberman et al. 1985). In a floristic study atLa Selva (J. S. Denslow and G. Chaverri, unpublisheddata) Euterpe occurred in plots on both the Arboleda


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2590 DEBORAH A. CLARK ET AL. Ecology, Vol. 76, No. 8

and Residual soils, but not on the two consociations ofthe Alluvium; Prestoea showed the opposite pattern.Determining the proximal causes of these edaphic

associations will require experimental work and inten-sive soil analysis. If Euterpe's distribution reflects low-ered competitive ability on more productive sites, suchcompetitive interactions must occur early in develop-ment. Even in the smallest (1-5 m) size class, Euterpewas virtually absent from the Alluvium. In contrast,the size-related increases in Prestoea's among-soil den-sity differences suggest continuing mortality effectsthrough regeneration. It is unlikely that direct com-petition between Euterpe and Prestoea causes their op-posite edaphic associations, given these developmentaldifferences and their relatively low densities.Iriartea, Socratea, and Welfia.-These palm speciesshowed no distributional variation with either topog-raphy or soil. Similarly, Iriartea deltoidea was foundby Phillips et al. (1994) in all seven forest types in alowland Amazonian reserve in Peru, and L exorrhizashowed no edaphic associations within a Brazilian Am-azonian forest (Kahn and de Castro 1985).Although Iriartea, Socratea, and Welfia were nearlyomnipresent in the four soil types, their densities variedgreatly within La Selva. Although their relation to theAlluvium is affected by human harvesting of Iriartea,among the other soils all three showed marked densitydifferences (Appendix).

Other sites.-There is increasing evidence of the im-portance of edaphically related spatial heterogeneitywithin old-growth tropical wet forests. Many cases areknown from Southeast Asia, from numerous small plotsover hundreds of square kilometres (cf. Brunei, Ashton1969; Sarawak, Baillie et al. 1987), to small-scale with-in-forest variation (four 1-ha plots, Sarawak, Newberyand Proctor 1984; 0.4 ha, subtropical Queensland, Wil-liams et al. 1969). Similar evidence has come fromneotropical wet forests. As in Asia, edaphic variationin forest composition has been found at all scales: fromvery local effects (within a 60 x 120 m plot, PuertoRico, Johnston 1992), to catenas or watersheds onscales of 0.5-500 ha (Central Amazon, Kahn and deCastro 1985, Peres 1994; French Guiana, Lescure andBoulet 1985; Puerto Rico, Basnet 1992; Guyana, terSteege et al. 1993). In Panama, Hubbell and Foster(1986) found half of the 303 tree and shrub species ina 50-ha plot to be significantly associated with one offour broad topographic site types.

Human impact in old-growthtropical rain forest

In addition to the now well-documented impacts ofedaphic variation, anthropogenic effects are a relativelylittle-studied but potentially important source of het-erogeneity within old-growth tropical forests. In thepresent study, the distribution of Iriartea revealed afootprint of human activities (Hamburg and Sanford1986) in forest previously considered "virgin."

Human activity is likely to have affected the com-position of most neotropical forests (e.g., Anderson1990, Gomez-Pompa and Kaus 1990, Garcia-Montieland Scatena 1994). In Panama, for example, the Guay-mi Indians practice selective silviculture in forests sim-ilar to La Selva (Gordon 1982). When clearing patchesof forest they protect Iriartea and Socratea, and theyoften plant these species, as well as Welfia, into their"tree gardens." Archaeological work at La Selva (I.Quintanilla, unpublished data cited by Horn and San-ford 1992) revealed habitation sites and pottery shardsfrom - BC 300 to AD 300; these pre-Columbians couldhave affected the composition of La Selva's currentoldgrowth. The distributional anomaly found for Iriartea,however, is likely to have resulted from more recentharvesting by local residents (otherwise, recolonizationfrom neighboring populations should have occurred).Given the increasing evidence of anthropogenic im-pacts within neotropical old growth, researchers study-ing the structure and function of these forests shouldexplicitly seek indications of human activities in theirstudy sites (Hamburg and Sanford 1986).

Interspecific interactions: the case ofIriartea and Socratea

The local abundances of these palms (Table 3) sug-gest some type of interspecific interaction. On the Re-sidual and Arboleda soils, these species showed recip-rocal density variation at all sizes (significant at 1-5m tall), and their summed density was remarkably sim-ilar between soils. On the Alluvium, the harvesting ofIriartea from the Experimental Consociation created anatural experiment. In all size classes, Socratea's cur-rent abundance is higher on the Experimental soil (Ir-iartea absent) than on the Holdridge (Iriartea present)(significant in the three larger size classes). No otherspecies varied in density between these consociations.Socratea and Iriartea would seem to have a lowprobability of interspecific encounter. Neither accountsfor >40-46% of the large palms per hectare in any sizeclass on any soil (Appendix), and 75% of the stems-10 cm dbh in this forest are nonpalms (Lieberman etal. 1985). Possible forms of interaction between thetwo include competition for pollinators or indirect ef-fects mediated by specific vesicular-arbuscular my-corrhizal fungi or natural enemies. Comparative fieldobservations and experiments to assess the factor(s)underlying these species' reciprocal distributionswould be very interesting. Such a study would be es-pecially valuable given the widespread human use ofIriartea deltoidea in neotropical forests (Pinard 1993,Phillips et al. 1994).

Methods for landscape-scale plantcommunity studies

The techniques in this study enabled a survey of palmdistributions and densities over a large area, revealedunrecognized spatial heterogeneity in the guild, and led


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to inferences about underlying factors. Both samplingmethods, however, have drawbacks. Although the Clos-est Individual technique produces quantitative densitydata, intersite density comparisons for individual spe-cies require equivalent overall density of the total guildbetween sites. With Closest Individuals evaluated on aspecies group basis, one abundant species could maskvariation in the others (taking data on each species ateach sample point would have required seven times thefield effort and would have involved data truncation atpoints where a species is absent or rare). The Presence/Absence sampling provided data on each species at allsample points, but within a variable "plot" size (dueto greater visibility in more open forest or steeper ter-rain). Additional noise in the data could result fromedaphic variability within the search area. Combiningmethods helped resolve these issues and strengthenedconclusions when the techniques produced equivalentpatterns. Based on this experience, however, we rec-ommend the following approach for studies of plantcommunity variation over large landscapes.

1) Distributing many sample points over the majorenvironmental gradients in the study area enables gen-eralization to the landscape. Such unbiased inferenceis difficult to attain from few samples or plots, es-pecially those not located with strict random sampling(see Botkin and Simpson 1990).2) To assess community or guild structure, we rec-ommend complete stem inventory and identificationwithin a small, standard-radius circular plot (largeenough to contain several stems of the target group) ateach sample point. This would provide data at eachpoint for each species of interest and would enableanalysis of presence/absence patterns and local density.With stem measurement, population structure could bequantified for more abundant species and for the spe-cies group as a whole. If not provided by a GIS or othermeans, field data on the topographic position, slope,and soil characteristics should be taken in each plot,to directly link the plant distributions to local site con-ditions. This small-plot method would provide morequantitative and more site-controlled data than thetechniques we used in the present study, at little ad-ditional field effort.

ConclusionsThe findings from this study and from many othersites indicate that tropical wet forests are characterized

by considerable internal heterogeneity in communitystructure. Much of this spatial variation is due to thefrequent occurrence of edaphic mosaics (varying soilchemistry and texture, drainage, and topography) with-in small-to-large landscapes in these forests. Additionalheterogeneity can derive from local human impacts,even in old-growth stands.Two challenging questions arise from this study. (1)What processes underly the nonuniform distributionsof the large palms at La Selva? For example, what

factors lead to the opposite distributions of Euterpe andPrestoea? Possibilities include differential impacts ofdrainage conditions or nutrients on their ability to growor survive in low light. More complex edaphic effectsmay produce the among-soil density changes in wide-spread species such as Welfia. What processes couldproduce the reciprocal densities of Socratea and Iriar-tea? Resolution of these issues will require field andshadehouse experiments (outplantings along soil/to-pographic gradients, soil trials with fertilization andwatering; cf. Goldberg 1982, Burslem et al. 1994). (2)Does high internal spatial heterogeneity promote theexceptional species richness of tropical wet forests (cf.Ashton 1969)? Do these forests have relatively moreplant species with strong edaphic associations and/ormore pronounced edaphic variability than less species-rich communities? Comparing these properties in tem-perate and tropical forests could be very revealing.ACKNOWLEDGMENTS

Wegratefullyacknowledge he financialsupportprovidedby the U.S. NationalScience Foundation BSR89-18185)andthe Andrew W. Mellon Foundation.Phil Sollins introducedus to La Selva's soil variability.LeonelCamposand WilliamBrenes carried out the field work and data input with skilland qualitycontrol. We also thank those interviewed aboutlocal uses of palms. We thank David Ackerly,Carol Aug-spurger,and Fred Scatenafor theirconstructivereviews ofthe manuscript, nd JennyJuarez or help withGIS mapping.The La SelvaGIS and reserve-widegridweremade possibleby donations o the Organizationor TropicalStudies(OTS)from the U.S. National Science Foundation,EnvironmentalSystems ResearchInstitute,the Andrew W. Mellon Foun-dation,and Sun Microsystems,Inc. We also thankOTS foron-going logistic support.

LITERATURE CITEDAnderson, A. B. 1990. Extraction and forest management byrural inhabitants in the Amazon estuary. Pages 65-85 inA. B. Anderson, editor. Alternatives to deforestation. Co-lumbia University Press, New York, New York, USA.Ashton, P. S. 1969. Speciation among tropical forest trees:some deductions in the light of recent evidence. BiologicalJournal of the Linnean Society 1:155-196.Baillie, I. C., P. S. Ashton, M. N. Court, J. A. R. Anderson,E. A. Fitzpatrick, and J. Tinsley. 1987. Site characteristicsand the distribution of tree species in Mixed Dipterocarp

Forest on Tertiary sediments in central Sarawak, Malaysia.Journal of Tropical Ecology 3:201-220.Basnet, K. 1992. Effect of topography on the pattern of treesin Tabonuco (Dacryodes excelsa) dominated rain forest inPuerto Rico. Biotropica 24:31-42.Botkin, D. B., and L. G. Simpson. 1990. Biomass of theNorth American boreal forest. Biogeochemistry 9:161-174.Burslem, D. F R. P., I. M. Turner, and P. J. Grubb. 1994.Mineral nutrient status of coastal hill dipterocarp forest andadinandra belukar in Singapore: bioassays of nutrient lim-itation. Journal of Tropical Ecology 10:579-599.Bush, M. B., and P. A. Colinvaux. 1994. Tropical forestdisturbance: paleoecological records from Darien, Panama.Ecology 75:1761-1768.Chauvel, A., Y. Lucas, and R. Boulet. 1987. On the genesisof the soil mantle of the region of Manaus, Central Ama-zonia, Brazil. Experientia 43:234-241.Chazdon, R. L. 1985. The palm flora of Finca La Selva.Principes 29:74-78.


13/15

2592 DEBORAH A. CLARK ET AL. Ecology, Vol. 76, No. 8Cottam, G., and J. T. Curtis. 1956. The use of distance mea-sures in phytosociological sampling. Ecology 37:451-460.Foster, R. B. 1990. The floristic composition of the Rio Manufloodplain forest. Pages 99-111 in A. H. Gentry, editor.Four neotropical rainforests. Yale University Press, NewHaven, Connecticut, USA.Garcia-Montiel, D. C., and F N. Scatena. 1994. The effectof human activities on the structure and composition of atropical forest in Puerto Rico. Forest Ecology and Man-agement 63:57-78.Gentry, A. H. 1982. Patterns of neotropical plant speciesdiversity. Evolutionary Biology 15:1-84.Gentry, A. H., and R. Ortiz S. 1993. Patrones de composicionfloristica en la Amazonia Peruana. Pages 155-166 in R.Kalliola, M. Puhakka, and W. Danjoy, editors. AmazoniaPeruana. PAUT and ONERN, Jyvaskyla, Finland.Goldberg, D. E. 1982. The distribution of evergreen anddeciduous trees relative to soil type: an example from theSierra Madre, Mexico, and a general model. Ecology 63:942-951.Gomez-Pompa, A., and A. Kaus. 1990. Traditional manage-

ment of tropical forests in Mexico. Pages 45-64 in A. B.Anderson, editor. Alternatives to deforestation. ColumbiaUniversity Press, New York, New York, USA.Gordon, B. L. 1982. A Panama forest and shore. BoxwoodPress, Pacific Grove, California, USA.Guillaumet, J.-L. 1987. Some structural and floristic aspectsof the forest. Experientia 43:241-25 1.Hamburg, S. P., and R. L. Sanford, Jr. 1986. Disturbance,Homo sapiens, and ecology. Bulletin of the Ecological So-ciety of America 67:169-17 1.Hartshorn, G. S. 1978. Tree falls and tropical forest dynam-ics. Pages 617-638 in P. B. Tomlinson and M. H. Zim-merman, editors. Tropical trees as living systems. Cam-bridge University Press, London, England.. 1983. Plants. Pages 118-157 in D. H. Janzen, editor.Costa Rican natural history. University of Chicago Press,Chicago, Illinois, USA.Hartshorn, G. S., and B. E. Hammel. 1994. Vegetation typesand floristic patterns. Pages 73-89 in L. A. McDade, K. S.Bawa, H. A. Hespenheide, and G. S. Hartshorn, editors.La Selva: ecology and natural history of a neotropical rainforest. University of Chicago Press, Chicago, Illinois, USA.Horn, S. P., and R. L. Sanford, Jr. 1992. Holocene fires inCosta Rica. Biotropica 24:354-361.Hubbell, S. P., and R. B. Foster. 1986. Commonness andrarity in a neotropical forest: implications for tropical treeconservation. Pages 205-231 in M. E. Soule, editor. Con-servation biology: the science of scarcity and diversity.Sinauer, Sunderland, Massachusetts, USA.Huston, M. A. 1980. Soil nutrients and tree species richnessin Costa Rican forests. Journal of Biogeography 7:147-157.Johnston, M. H. 1992. Soil-vegetation relationships in a ta-bonuco forest community in the Luquillo Mountains ofPuerto Rico. Journal of Tropical Ecology 8:253-263.Jordan, C. E 1985. Soils of the Amazon forest. Pages 83-94 in G. T. Prance and T. E. Lovejoy, editors. Amazonia.Pergamon, New York, New York, USA.Kahn, E, and A. de Castro. 1985. The palm community ina forest of Central Amazonia, Brazil. Biotropica 17:210-216.Lescure, J. P., and R. Boulet. 1985. Relationships betweensoil and vegetation in a tropical rain forest in French Gui-ana. Biotropica 17:155-164.

Levin, S. A. 1992. The problem of pattern and scale in ecol-ogy. Ecology 73:1943-1967.Lieberman, D., G. S. Hartshorn, M. Lieberman, and R. Per-

alta. 1990. Forest dynamics at La Selva Biological Station,1969-1985. Pages 509-521 in A. H. Gentry, editor. Fourneotropical rainforests. Yale University Press, New Haven,Connecticut, USA.Lieberman, M., D. Lieberman, G. S. Hartshorn, and R. Per-alta. 1985. Small-scale altitudinal variation in lowland wettropical forest vegetation. Journal of Ecology 73:505-516.McDade, L. A., and G. S. Hartshorn. 1994. La Selva Bio-logical Station. Pages 6-14 in L. A. McDade, K. S. Bawa,H. A. Hespenheide, and G. S. Hartshorn, editors. La Selva:ecology and natural history of a neotropical rain forest.University of Chicago Press, Chicago, Illinois, USA.Newbery, D. McC., and J. Proctor. 1984. Ecological studiesin four contrasting lowland rain forests in Gunung MuluNational Park, Sarawak. Journal of Ecology 72:475-493.Oliveira-Filho, A. T., E. A. Vilela, D. A. Carvalho, and M.L. Gavilanes. 1994. Effects of soils and topography on thedistribution of tree species in a tropical riverine forest insouth-eastern Brazil. Journal of Tropical Ecology 10:483-508.Peres, C. A. 1994. Composition, density, and fruiting phe-nology of arborescent palms in an Amazonian terra firmeforest. Biotropica 26:285-294.Phillips, O., A. H. Gentry, C. Reynel, P. Wilkin, and B. Gal-vez-Durand. 1994. Quantitative ethnobotany and Ama-zonian conservation. Conservation Biology 8:225-248.Pinard, M. 1993. Impacts of stem harvesting on populationsof Iriartea deltoidea (Palmae) in an extractive reserve inAcre, Brazil. Biotropica 25:2-14.Ruokolainen, K., and H. Tuomisto. 1993. La vegetacion deterrenos no inundables (tierra firme) en la selva baja de laAmazonia Peruana. Pages 139-153 in R. Kalliola, M. Pu-hakka, and W. Danjoy, editors. Amazonia Peruana. PAUTand ONERN, Jyvaskyla, Finland.Salo, J., and M. Rasanen. 1989. Hierarchy of landscape pat-terns in western Amazon. Pages 35-45 in L. B. Holm-Nielsen, I. C. Nielsen, and H. Balslev, editors. Tropicalforests: botanical dynamics, speciation and diversity. Ac-ademic Press, New York, New York, USA.Sancho M., E, and R. Mata Ch. 1987. Estudio detallado desuelos, Estaci6n Biol6gica "La Selva." Organization forTropical Studies, San Jos6, Costa Rica.Sanford, R. L., H. E. Braker, and G. S. Hartshorn. 1986.Canopy openings in a primary neotropical lowland forest.Journal of Tropical Ecology 2:277-282.Sanford, R. L., Jr., P. Paaby, J. C. Luvall, and E. Phillips.1994. Climate, geomorphology, and aquatic systems. Pages19-33 in L. A. McDade, K. S. Bawa, H. A. Hespenheide,and G. S. Hartshorn, editors. La Selva: ecology and naturalhistory of a neotropical rain forest. University of ChicagoPress, Chicago, Illinois, USA.Sollins, P., E Sancho M., R. Mata Ch., and R. L. Sanford, Jr.1994. Soils and soil process research. Pages 34-53 in L.A. McDade, K. S. Bawa, H. Hespenheide, and G. S. Hart-shorn, editors. La Selva: ecology and natural history of aneotropical rainforest. University of Chicago Press, Chi-cago, Illinois, USA.ter Steege, H., V. G. Jetten, A. M. Polak, and M. J. A. Werger.1993. Tropical rain forest types and soil factors in a wa-tershed area in Guyana. Journal of Vegetation Science 4:705-716.Uhl, N. W., and J. Dransfield. 1987. Genera palmarum. AllenPress, Lawrence, Kansas, USA.Williams, W. T., G. N. Lance, L. J. Webb, J. G. Tracey, andJ. H. Connell. 1969. Studies in the numerical analysis ofcomplex rain-forest communities. IV. A method for theelucidation of small-scale forest pattern. Journal of Ecology57:635-654.


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December 1995 TROPICAL PALM COMMUNITY STRUCTURE 2593APPENDIX

Density of the five abundant palm species by size and soil type. For the Alluvium, data are presented both for the overallsoil type and separately by consociation (Experimental, Holdridge). Probabilities are for chi-square tests of the numbers ofClosest Individuals that were and were not a given species, across soils. When total palm density does not differ amongsoils, this tests for variation in a given species' density across soils (see Methods). Only in the 1-5 m height class did totaldensity vary among soils (see Results); for this size, P* is for a chi-square test (as above) of a species' representation amongClosest Individuals on the three soil types of equivalent palm density (Residual, Arboleda, and Alluvium).Density (stems/ha)

Height class (m): 1-5 >5-10 >10-15 >15Euterpe macrospadix

Soil typeResidual 45.0 6.7 5.1 6.3Arboleda 17.1 3.7 1.5 4.0Stream 28.0 0.0 2.8 2.4Alluvium 6.6 0.0 0.0 0.0

P 0.001*


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2594 DEBORAH A. CLARK ET AL. Ecology, Vol. 76, No. 8APPENDIX. Continued.

Density (stems/ha)Height class (m): 1-5 >5-10 >10-15 >15

Welfia georgiiSoil typeResidual 177.0 29.5 14.8 8.6Arboleda 199.0 35.8 16.3 14.8Stream 53.2 21.3 10.6 8.3Alluvium 319.3 23.1 10.7 15.8

P 0.02* NS NS 0.0000Consociation

Experimental 404.8 21.7 8.8 15.9Holdridge 245.5 25.0 13.2 15.6P NS NS NS NS

clark & clark

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