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Aim A major floristic and climatic transition from aseasonal to seasonalevergreen tropical forest (the Kangar–Pattani Line; KPL) exists in the Indo-Sundaic region of Southeast Asia. Mechanisms constraining species distributionhere are at present poorly understood, but it is hypothesized that species differ intheir tolerances of abiotic factors, in particular water availability. Under thishypothesis, we anticipate differences in performance or habitat preferences, orboth, of species differing in distribution with respect to the KPL. The aim of thisstudy is to test whether geographical distributions can be used to explainvariation in growth, mortality and habitat preferences in co-occurring tree speciesdiffering in their distribution in relation to the KPL.Location Pasoh Forest Reserve, Negeri Sembilan, Malaysia; south of the KPL.Methods All tree species within a 50-ha forest dynamics plot were classified aswidespread or southern based upon their distributions in relation to the KPL andas habitat specialists or generalists based on spatial association with soil-basedhabitat categories. Growth and mortality rates, variation in growth and mortalitywith respect to soil type, and levels of habitat association were quantified forspecies with different geographical distributions.Results Differences existed in species performance based upon geographicaldistributions. Specifically, widespread species had lower growth rates than didspeciesrestrictedtotheaseasonalforests.Mortalityratesdidnotdifferasafunctionof geographical distribution. The growth responses of species to soil habitats alsodiverged, such that differences in performance of widespread species among soiltypesweremoreconservativethanthoseofspeciesrestrictedintheirdistributiontothe aseasonal forests. However, the proportion of species showing positive habitatassociations did not differ significantly between widespread and southern species.Main conclusions Distribution-based differences in species performance andresponse to soil type support the hypothesis that species tolerant of wider climaticvariation perform less well in any given environment due to limitations onplasticity. These performance differences provide quantitative evidence of the roleof climatic transitions in determining tree species distributions in relation to theKangar–Pattani Line in the Indo-Malay region. Such differences in performancehave important implications for our understanding of biodiversity gradients andresponses of Indo-Sundaic forests to climate change.KeywordsAbiotic resource requirements, geographical range, habitat association, plasti-city, rainfall seasonality, Southeast Asia, stress tolerance, performance trade-offs,tropical trees.

Tropical forests vary substantially in the densities of trees of different sizes and thus in above-ground biomass and carbon stores. However, these tree size distributions show fundamental similarities suggestive of underlying general principles. The theory of metabolic ecology predicts that tree abundances will scale as the -2 power of diameter. Demographic equilibrium theory explains tree abundances in terms of the scaling of growth and mortality. We use demographic equilibrium theory to derive analytic predictions for tree size distributions corresponding to different growth and mortality functions. We test both sets of predictions using data from 14 large-scale tropical forest plots encompassing censuses of 473 ha and > 2 million trees. The data are uniformly inconsistent with the predictions of metabolic ecology. In most forests, size distributions are much closer to the predictions of demographic equilibrium, and thus, intersite variation in size distributions is explained partly by intersite variation in growth and mortality.

Premise of the study: We tested the credibility and significance of digital field photographs as supplements or substitutes for conventional herbarium specimens with particular relevance to exploration of the tropics. Methods: We made 113 collections in triplicate at a species-rich mountain in the Philippines while we took 1238 digital photographs of the same plants. We then identified the plants from the photographs alone, categorized the confidence of the identification and the reason for failure to identify, and compared the results to identifications based on the dried specimens. Results: We identified 72.6% of the photographic sets with high confidence and 27.4% with low confidence or only to genus. In no case was a confident identification altered by subsequent examination of the dried specimen. The failure to identify photographic sets to species was due to the lack of a key feature in 67.8% of the cases and due to a poorly understood taxonomy in 32.2%. Discussion: We conclude that digital photographs cannot replace traditional herbarium specimens as the primary elements that document tropical plant diversity. However, photographs represent a new and important artifact that aids an expedient survey of tropical plant diversity while encouraging broad public participation.

The establishment and growth of a young tree requires a microsite that falls within a range of specific environmental conditions. Microsites will to some degree be modified by such neighbouring plants as are already established, a circumstance that will in turn lead to either a positive or negative spatial association among the individuals. Such patterns of spatial interactions are amenable to statistical inference. Positive associations may result when one species ameliorates overall hostile conditions, such as the shade and moisture provided the seedlings of long-leaf pine by the canopy of the saw palmetto (Allen 1956). Indeed, positive associations appear widespread in arid and cold habitats (reviewed in Tirado & Pugnaire 2003). However, on the forest floor of the humid tropics, negative associations are presumably more likely (Montgomery 2004). Harms et al. (2004) recently found a correlation between high density of small palms and a low density of tree saplings across four Neotropical sites, while Wang & Augspurger (2004) demonstrated that dwarf palms and cyclanths reduce seedling recruitment on the forest floor in Costa Rica. We investigated the spatial co-occurrence of understorey palms in the genus Licuala (Arecaceae) with the saplings of trees recruited into a permanent plot of lowland tropical forest in Malaysia. Licuala is a genus of 110 species of long-lived, short-stemmed or caespitose palms indigenous to South-East Asia and the Western Pacific where they create a characteristic appearance within forest understorey (Saw 1994). They bear fan-shaped leaves with blades 1–2 m across and typically incised in wedge-shaped portions. The petioles range up to 3 m long

Relationships between spatial distributions and site conditions, namely topography and soil texture, were analyzed for two congeneric emergent trees, Dryobalanops aromatica and Dryobalanops lanceolata (Dipterocarpaceae), in a tropical rainforest in Sarawak, East Malaysia. A 52-ha permanent plot was divided into 1300 quadrats measuring 20 m × 20 m; for each Dryobalanops species, the number and total basal area of trees ≥1 cm in d.b.h. were compared among groups of quadrats with different site conditions. Because spatial distributions of both Dryobalanops and site-condition variables were aggregated, Monte-Carlo permutation tests were applied to analyze the relationships. Both single and multifactor statistical tests showed that the density and basal area distributions of the two species were significantly non-random in relation to soil texture and topographic variables. D. aromatica was significantly more abundant at higher elevations, in sandy soils, and on convex and steep slopes. In contrast, D. lanceolata preferred lower elevations and less sandy soils. In the study plot, there were very few sites (3 of 1150 quadrats tested) where the models of Hayashi’s method predicted the co-occurrence of the two species. These results suggest that between-species differences in habitat preferences are so large that they alone explain the spatially segregated distributions of these two species within the 52-ha study plot.

The diversity and niche specificity of hemi-epiphytic figs in a lowland dipterocarp forest in Sarawak were investigated in 1998. Twenty-seven fig species (264 individuals, c. 120 ha) colonized a diversity of host taxa (35 families), but densities were very low and only 1.77% of trees> 30 cm d.b.h. were occupied. There were no significant associations with host taxa or host-bark roughness but among 11 common species (≥9 individuals) the distributions of all other parameters (host-d.b.h., height and position of colonization, crown illumination, soil-texture and slope-angle) were significantly different, and we identified five fig guilds. The guilds corresponded to canopy strata, and appeared to reflect the establishment microsite requirements of different species. A fundamental trade-off within the hemi-epiphytic habit was revealed: Species colonizing larger hosts were rarer, because of lower host densities and more specific microsite requirements, but had better light environments and attained a larger maximum size. The single strangler species appeared to escape many of these constraints, and an important source of mortality caused by host-toppling, indicating the advantages of this strategy. Thus, the hemi-epiphytic figs in this community have come to fill a remarkable diversity of niches, despite low levels of competition, through the exigencies of a complex environment. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 439–455

Population structure and spatial patterns were examined for four species of canopy dipterocarps (Anisoptera costata, Dipterocarpus alatus, Hopea odorata, Vatica cinerea) in a 50 ha plot in seasonal dry evergreen forest at the Huai Kha Khaeng Wildlife Sanctuary in western Thailand. Spatial dispersion was assessed with Morisita’s index for quadrat sizes ranging from 61 m2 to 25 ha; spatial attraction and repulsion between species and size classes were measured with Iwao’s index. Only Vatica had a negative exponential diameter distribution suggesting continuous recruitment. The other species had either normal (Hopea) or irregular diameter distributions with peaks in the large size classes (Anisoptera, Dipterocarpus). All four species were significantly clumped at most quadrat sizes. At the local scale, saplings and poles of Hopea and Anisoptera were negatively associated with adults at quadrat sizes

The rooting ability of branch cuttings was evaluated for 100 tree species (including 41 families and 78 genera) collected in a tropical rainforest in Sarawak, Malaysia. Leafy cuttings of natural forest saplings were planted in a non-mist propagation system with IBA treatment. During the 6-month experiment, 66 species were rooted with an overall mean rooting percentage of 37.7% (range 0–100%). Species in the families Dipterocarpaceae and Lauraceae had a low rooting ability, whereas those in Euphorbiaceae, Rubiaceae, and Annonaceae had a high rooting ability. Differences in rooting ability were related to species-specific mature sizes, diameter growth rates and habitat preferences. Species of smaller mature sizes and faster diameter growth rates showed better rooting ability. Species whose forest saplings sprouted more vigorously after experimental felling rooted better than those that showed less vigorous sprouting. Species whose habitats were on lower elevations, concave slopes, and/or clay-rich soils rooted significantly better than those that preferred opposite habitats or habitat generalists that showed no significant habitat preference. The implications of these relations are discussed from the viewpoint of saplings’ adaptation to physical damage in their natural habitats.

Abundance and richness are the two fundamental components of speciesdiversity. They represent two distinct types of variables of which the formerisadditive when aggregated across scales while the latter is nonadditive. Thisstudy investigated the changes in the spatial patterns of abundance andrichnessof tree species across multiple scales in a tropical rain forest of Malaysiaandtheir variations in different regions of the study area. The results showedthatfrom fine to coarse scales abundance had a gradual and systematic change inpattern, whereas the change in richness was much less predictable and a‘hotspot’ in richness at one scale may become a‘coldspot’ at another. The study also demonstrated that differentmeasures of diversity variation (e.g., variance and coefficient of variation)can result in different or even contradictory results which further complicatedthe interpretation of diversity patterns. Because of scale effect the commonlyused measure of species diversity in terms of unit area (e.g.,species/m2) is misleading and of little use in comparing speciesdiversitybetween different ecosystems. Extra care must be taken if management andconservation of species diversity have to be based on information gathered at asingle scale.

Spatial patterns of tree species were studied in a 50-ha tropical rain forest plot in the Pasoh forest, Malaysia. This forest is characterized by a high diversity and very high number of rare species. Out of the 745 species occurring with > five individuals, 80.4 % had an aggregated distribution, 19.5% were randomly distributed and one species had a regu- lar distribution. The spatial patterns of rare vs. common spe- cies, juvenile vs. adult trees, and coarse vs. fine scales were compared. Rare species are generally less aggregated than common ones and most of the randomly distributed species are rare. Spatial patterns shift from high clumping to looser intensity or random distribution when moving from juveniles to adults for the same species. No adult tree species display a regular pattern, however. Regular distributions were rarely found; this is probably due to intraspecific competition at a local scale. There is a negative correlation between per capita death rate and population density. This study suggests that the Pasoh forest and its high diversity are subjected to multiple controlling factors, e.g., topography, spacing effect, density-dependent processes and species rarity. The importance of any factor changes across spatial and temporal scales.

The diversity of trees (species richness, abundance and Shannon diversity) in a tropical rain forest of Malaysia has been studied from the point of view of its spatial organization in order to formulate hypotheses about the origin of the observed spatial patterns. The question that motivated this study is whether tropical forests communities are in a state of equilibrium or non- equilibrium. Three aspects have been examined: (1) changes in diversity were studied with respect to sampling area and sampling designs. A minimum area of 5-10 ha is recommended by the species-area curves, while 2-5 ha seem appropriate based on the Shannon diversity-area curves. Different sampling designs significantly affect the species-area curves. The power function, which can be derived under the equilibrium assumption, is not appropriate to fit the observed diversity-area curves. (2) The spatial features of diversity variables were then studied. Variograms showed that there are dominant short-range effects (around 150 m), obvious anisotropic distribution, and high random variation in the diversity data. (3) Partitioning the variation of the diversity measures into environmental (topographic) and spatial components indicated that the spatial organisation of that community was mostly unpredictable. There may be many processes controlling the formation of the spatial patterns in the tropical rain forest. Unidentified causes, affecting mainly the small-scale processes (

Scale is emerging as one of the critical problems in ecology because our perception of most ecological variables and processes depends upon the scale at which the variables are measured. A conclusion obtained at one scale may not be valid at another scale without sufficient knowledge of the scaling effect, which is also a source of misinterpretation for many ecological problems, such as the design of reserves in conservation biology. This paper attempts to study empirically how scaling may affect the spatial patterns of diversity (tree density, richness and Shannon diversity) that we may perceive in tropical forests, using as a test-case a 50 ha forest plot in Malaysia. The effect of scale on measurements of diversity patterns, the occurrence of rare species, the fractal dimension of diversity patterns, the spatial structure and the nearest-neighbour autocorrelation of diversity are addressed. The response of a variable to scale depends on the way it is measured and the way it is distributed in space. We conclude that, in general, the effect of scaling on measures of biological diversity is non-linear; heterogeneity increases with the size of the sampling units, and fine-scale information is lost at a broad scale. Our results should lead to a better understanding of how ecological variables and processes change over scale.

The population biology ofAquilaria malaccensis, one source of gharu, and Cinnamomum mollissimum, one source of wild cinnamon, was studied in a 50 ha permanent plot of primary rain forest in Malaysia. Median diameter growth rates of 0.22 cm yr-1 and 0.1 cm yr-1 should not be prohibitive of economic exploitation, and suggest that the trees could be grown commercially. However, the natural densities were between 2 and 3 trees over 1 cm d.b.h. per ha, which is roughly the median for all trees in the plot, would preclude economic exploitation of these natural populations. The economics of harvesting natural populations is considered in a preliminary fashion by allowing favorable assumptions of quantity and quality of production. The price likely to be fetched from either a first time extraction (on the order of US$10.00 per ha) or from sustained production (on the order of US$0.10 per ha per yr), are too small to be of interest as single-product schemes, and are negligible compared to the extraction of multi-species crops of timber. However, it is possible that by combining multiple products under a “High Diversity Forestry” scheme, one could increase the density of harvestable products, reduce the unit cost of labor and improve the economic portrait.

An inventory was made of 50 ha of primary lowland rain forest in Peninsular Malaysia, in which ca. 340,000 trees 1 cm dbh or larger were measured and identified to species. Out of a total plot tree flora of 820 species, 76 species are known to bear edible fruit. Especially diverse were the wild species of mango (Mangifera, Anacardiaceae, 12 spp.), mangosteen (Garcinia, Clusiaceae, 13 spp.), breadfruit (Artocarpus, Moraceae, 10 spp.) and rambutan (Nephelium, Sapindaceae, 5 spp.). Median population size for all species of fruit trees was 3.0 trees per ha and 0.2 adult trees per ha. Direct economic value of wild fruit trees was small; only one species has been very much collected and sold, Parkia speciosa (Fabaceae), amounting to less than US$20 per ha per year. The potential value of the species as genetic resources is very large: 24 species are cultivated, 38 edible species are congeneric with cultivated crops and at least 10 other species bear inedible fruit but are related to cultivated crops. We conclude that the Peninsular Malaysian rain forest is exceedingly rich in wild fruit trees, that these normally live at low densities, and that their principal economic value is as genetic resources.

In Amazonian tropical forests, recent studies have reported increases in aboveground biomass and in primary productivity, as well as shifts in plant species composition favouring fast-growing species over slow-growing ones. This pervasive alteration of mature tropical forests was attributed to global environmental change, such as an increase in atmospheric CO2 concentration, nutrient deposition, temperature, drought frequency, and/or irradiance. We used standardized, repeated measurements of over 2 million trees in ten large (16–52 ha each) forest plots on three continents to evaluate the generality of these findings across tropical forests. Aboveground biomass increased at seven of our ten plots, significantly so at four plots, and showed a large decrease at a single plot. Carbon accumulation pooled across sites was significant (+0.24 MgC ha−1 y−1, 95% confidence intervals [0.07, 0.39] MgC ha−1 y−1), but lower than reported previously for Amazonia. At three sites for which we had data for multiple census intervals, we found no concerted increase in biomass gain, in conflict with the increased productivity hypothesis. Over all ten plots, the fastest-growing quartile of species gained biomass (+0.33 [0.09, 0.55] % y−1) compared with the tree community as a whole (+0.15 % y−1); however, this significant trend was due to a single plot. Biomass of slow-growing species increased significantly when calculated over all plots (+0.21 [0.02, 0.37] % y−1), and in half of our plots when calculated individually. Our results do not support the hypothesis that fast-growing species are consistently increasing in dominance in tropical tree communities. Instead, they suggest that our plots may be simultaneously recovering from past disturbances and affected by changes in resource availability. More long-term studies are necessary to clarify the contribution of global change to the functioning of tropical forests., Author Summary Recent studies have reported major changes in mature tropical forests, with increases in both forest biomass and net primary productivity, as well as shifts in plant species composition that favour fast-growing species over slow-growing ones. These pervasive alterations were attributed to global environmental change, and may result in dramatic shifts in the functioning of tropical forest ecosystems. We reassessed these findings using a dataset of large permanent forest plots on three continents. We found that tree biomass increased at seven of our ten plots, and showed a large decrease at a single plot. Overall, this increase was significant, albeit lower than reported previously for Amazonian forests. At three sites for which we had data for multiple census intervals, we found no concerted increase in biomass gain, in conflict with the increased productivity hypothesis. With the exception of one plot, slow-growing species gained more biomass than either fast-growing species or the tree community as a whole. Hence, our results do not support the hypothesis that fast-growing species are consistently increasing in dominance in tropical tree communities. Overall, our results suggest that our plots may be simultaneously recovering from past disturbances and affected by changes in resource availability., An analysis of changes in biomass and primary productivity across ten large tropical forest plots revealed that aboveground biomass increased significantly, fast-growing species increased significantly in dominance at a single site, and slow-growing species increased significantly at half of our sites.

Until now, there have been few research works on Cambodian forests because of the long period of civil war, which restricted forest researchers and surveyors in the area. This book presents many new topics of research in forests such as those of Cambodia which were unavailable until now. One of the most attractive features of the volume is that it fills the gaps in data about the world’s forests. The book consists of three parts: forest hydrology, forest management, and forest ecology, designed to provide an understanding of continental river basins. The latest data are presented here, as derived from advanced observation systems for atmospheric flux, ground water level, soil water movement, and stable isotope variation as well as remote sensing, which are used for continuous measurements of forest environments. These research results provide a bounty of fresh scientific information, creating a valuable resource not only for researchers and university students but also for forest administrators. Table of contents Part 1: Forest Hydrology Part II: Forest Management Part III: Forest Ecology

Most ecological hypotheses about species coexistence hinge on species differences, but quantifying trait differences across species in diverse communities is often unfeasible. We examined the variation of demographic traits using a global tropical forest data set covering 4500 species in 10 large-scale tree inventories. With a hierarchical Bayesian approach, we quantified the distribution of mortality and growth rates of all tree species at each site. This allowed us to test the prediction that demographic differences facilitate species richness, as suggested by the theory that a tradeoff between high growth and high survival allows species to coexist. Contrary to the prediction, the most diverse forests had the least demographic variation. Although demographic differences may foster coexistence, they do not explain any of the 16-fold variation in tree species richness observed across the tropics.

The theory of metabolic ecology predicts specific relationships among tree stem diameter, biomass, height, growth and mortality. As demographic rates are important to estimates of carbon fluxes in forests, this theory might offer important insights into the global carbon budget, and deserves careful assessment. We assembled data from 10 oldgrowth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to test the theory’s predictions. We also developed a set of alternative predictions that retained some assumptions of metabolic ecology while also considering how availability of a key limiting resource, light, changes with tree size. Our results show that there are no universal scaling relationships of growth or mortality with size among trees in tropical forests. Observed patterns were consistent with our alternative model in the one site where we had the data necessary to evaluate it, and were inconsistent with the predictions of metabolic ecology in all forests.

An ecological community's species diversity tends to erode through time as a result of stochastic extinction, competitive exclusion, and unstable host-enemy dynamics. This erosion of diversity can be prevented over the short term if recruits are highly diverse as a result of preferential recruitment of rare species or, alternatively, if rare species survive preferentially, which increases diversity as the ages of the individuals increase. Here, we present census data from seven New and Old World tropical forest dynamics plots that all show the latter pattern. Within local areas, the trees that survived were as a group more diverse than those that were recruited or those that died. The larger (and therefore on average older) survivors were more diverse within local areas than the smaller survivors. When species were rare in a local area, they had a higher survival rate than when they were common, resulting in enrichment for rare species and increasing diversity with age and size class in these complex ecosystems.

A 52 hectare permanent research plot was established in Lambir Hills National Park to enable long-term study of factors controlling the origin and maintenance of tree diversity. In this chapter we summarize some of our recent work on the relationships between floristic variation and edaphic heterogeneity in the Lambir forest. First, we provide a general description of the floristic composition of this hyperdiverse forest. Second, we use a detailed survey of soil chemistry to test whether floristic composition changes in relation to edaphic characteristics. We also assess the extent to which individual species have non-random distributions in the forest with respect to edaphic heterogeneity. Finally, to investigate the influence of habitat variation on floristic diversity we compare our results from the heterogeneous forest at Lambir Hills with a more homogeneous forest in Peninsular Malaysia.

Stand structure and floristic composition of the 50-ha Forest Research Plot in Pasoh Forest Reserve (Pasoh FR) are described. Pasoh FR was found to have extremely high tree species diversity. In the 50-ha plot there were 338,924 trees with a total basal area of 1,659 m2, comprising 818 tree species in 295 genera and 81 families. The Euphorbiaceae (85 species) was the most species-rich family. The Dipterocarpaceae dominated the forest with 27% of the basal area, and eight of the top 10 basal-area contributing species. The Fabaceae, Euphorbiaceae and Burseraceae were the next most important large trees in the plot. Shorea had the highest basal area and stem number. Syzygium was the richest genus with 45 species. As with other Asian tropical forests there were many speciose genera in the plot; 11 genera had ≧ 12 species. Floristic composition and stand structure varied across the 50-ha plot in relation to edaphic and topographic variation. Multivariate analyses revealed three main community types: a swamp community in the lowest areas of the plot, a hill community, and an alluvial forest community in mid to lower elevations in the plot. In addition, the alluvial community appears to be divisible into three types based on differences in soil properties. In addition to describing species characteristic of each of these community types, we also describe some of the distinctive life-history and evolutionary characteristics of the Pasoh FR. This chapter provides a basis for future work at Pasoh FR.

Dynamics of the Pasoh forest in Peninsular Malaysia were assessed by drawing a comparison with a forest in Panama, Central America, whose dynamics have been thoroughly described. Census plots of 50 ha were established at both sites using standard methods. Tree mortality at Pasoh over an eight–year interval was 1.46% yr −1 for all stems greater than or equal to 10 mm diameter at breast height (dbh), and 1.48% yr −1 for stems greater than or equal to 100 mm dbh. Comparable figures at the Barro Colorado Island site in Panama (BCI) were 2.55% and 2.03%. Growth and recruitment rates were likewise considerably higher at BCI than at Pasoh. For example, in all trees 500 to 700 mm in dbh, mean BCI growth over the period 1985 to 1995 was 6 mm yr −1 , whereas mean Pasoh growth was about 3.5 mm yr −1 . Examining growth and mortality rates for individual species showed that the difference between the forests can be attributed to a few light–demanding pioneer species at BCI, which have very high growth and mortality; Pasoh is essentially lacking this guild. The bulk of the species in the two forests are shade–tolerant and have very similar mortality, growth and recruitment. The Pasoh forest is more stable than BCI's in another way as well: few of its tree populations changed much over the eight–year census interval. In contrast, at BCI, over 10% of the species had populations increasing or decreasing at a rate of > 0.05 yr −1 (compared to just 2% of the species at Pasoh). The faster species turnover at BCI can probably be attributed to severe droughts that have plagued the forest periodically over the past 30 years; Pasoh has not suffered such extreme events recently. The dearth of pioneer species at Pasoh is associated with low–nutrient soil and slow litter breakdown, but the exact mechanisms behind this association remain poorly understood.

The relationship between species diversity and sampled area is fundamental to ecology. Traditionally, theories of the species–area relationship have been dominated by random-placement models. Such models were used to formulate the canonical theory of species–area curves and species abundances. In this paper, however, armed with a detailed data set from a moist tropical forest, we investigate the validity of random placement and suggest improved models based upon spatial aggregation. By accounting for intraspecific, small-scale aggregation, we develop a cluster model which reproduces empirical species–area curves with high fidelity. We find that inter-specific aggregation patterns, on the other hand, do not affect the species–area curves significantly. We demonstrate that the tendency for a tree species to aggregate, as well as its average clump size, is not significantly correlated with the species' abundance. In addition, we investigate hierarchical clumping and the extent to which aggregation is driven by topography. We conclude that small-scale phenomena such as dispersal and gap recruitment determine individual tree placement more than adaptation to larger-scale topography.

A fundamental question in ecology is how many species occur within a given area. Despite the complexity and diversity of different ecosystems, there exists a surprisingly simple, approximate answer: the number of species is proportional to the size of the area raised to some exponent. The exponent often turns out to be roughly 1/4. This power law can be derived from assumptions about the relative abundances of species or from notions of self-similarity. Here we analyze the largest existing data set of location-mapped species: over one million, individually identified trees from five tropical forests on three continents. Although the power law is a reasonable, zeroth-order approximation of our data, we find consistent deviations from it on all spatial scales. Furthermore, tropical forests are not self-similar at areas ≤50 hectares. We develop an extended model of the species-area relationship, which enables us to predict large-scale species diversity from small-scale data samples more accurately than any other available method.

Fully mapped tree census plots of large area, 25 to 52 hectares, have now been completed at six different sites in tropical forests, including dry deciduous to wet evergreen forest on two continents. One of the main goals of these plots has been to evaluate spatial patterns in tropical tree populations. Here the degree of aggregation in the distribution of 1768 tree species is examined based on the average density of conspecific trees in circular neighborhoods around each tree. When all individuals larger than 1 centimeter in stem diameter were included, nearly every species was more aggregated than a random distribution. Considering only larger trees (≥ 10 centimeters in diameter), the pattern persisted, with most species being more aggregated than random. Rare species were more aggregated than common species. All six forests were very similar in all the particulars of these results.

In this early report of a global program of tropical rain forest research, the causes of tree species diversity are examined through comparisons at global, regional and local scales. Species diversity in communities of sessile organisms has been attributed to many factors. Hypotheses which address two of these, Connell’s on intermediate levels of disturbance and Tilman’s on competition for heterogeneous soil resources, are reviewed and clarified in context of exceptionally rich communities. Our evidence suggests that many factors are important, but at varying scales in space and time. These differing scales will be discussed with reference to our new data. Unresolved impediments to the community drift hypothesis will be presented. In the summary, lessons for conservation will be identified

Changes in plant phenology will be one of the earliest responses to rapid global climate change and could potentially have serious consequences both for plants and for animals that depend on periodically available plant resources. Phenological patterns are most diverse and least understood in the tropics. In those parts of tropical Asia where low temperature or drought impose a seasonal rest period, regular annual cycles of growth and reproduction predominate at the individual, population, and community level. In aseasonal areas, individuals and populations show a range of sub- to supra-annual periodicities, with an overall supra-annual reproductive periodicity at the community level. There is no evidence for photoperiod control of phenology in the Asian tropics, and seasonal changes in temperature are a likely factor only near the northern margins. An opportunistic response to water availability is the simplest explanation for most observed patterns where water is seasonally limiting, while the great diversity of phenological patterns in the aseasonal tropics suggests an equal diversity of controls. The robustness of current phenological patterns to high interannual and spatial variability suggests that most plant species will not be seriously affected by the phenological consequences alone of climate change. However, some individual plant species may suffer, and the consequences of changes in plant phenology for flower-and fruit-dependent animals in fragmented forests could be serious.

1 Species-accumulation curves for woody plants were calculated in three tropical forests, based on fully mapped 50-ha plots in wet, old-growth forest in Peninsular Malaysia, in moist, old-growth forest in central Panama, and in dry, previously logged forest in southern India. A total of 610 000 stems were identified to species and mapped to < Im accuracy. Mean species number and stem number were calculated in quadrats as small as 5 m x 5 m to as large as 1000 m x 500 m, for a variety of stem sizes above 10 mm in diameter. Species-area curves were generated by plotting species number as a function of quadrat size; species-individual curves were generated from the same data, but using stem number as the independent variable rather than area. 2 Species-area curves had different forms for stems of different diameters, but species-individual curves were nearly independent of diameter class. With < 10(4) stems, species-individual curves were concave downward on log-log plots, with curves from different forests diverging, but beyond about 104 stems, the log-log curves became nearly linear, with all three sites having a similar slope. This indicates an asymptotic difference in richness between forests: the Malaysian site had 2.7 times as many species as Panama, which in turn was 3.3 times as rich as India. 3 Other details of the species-accumulation relationship were remarkably similar between the three sites. Rectangular quadrats had 5-27% more species than square quadrats of the same area, with longer and narrower quadrats increasingly diverse. Random samples of stems drawn from the entire 50 ha had 10-30% more species than square quadrats with the same number of stems. At both Pasoh and BCI, but not Mudumalai. species richness was slightly higher among intermediate-sized stems (50-100mm in diameter) than in either smaller or larger sizes, These patterns reflect aggregated distributions of individual species, plus weak density-dependent forces that tend to smooth the species abundance distribution and 'loosen' aggregations as stems grow. 4 The results provide support for the view that within each tree community, many species have their abundance and distribution guided more by random drift than deterministic interactions. The drift model predicts that the species-accumulation curve will have a declining slope on a log-log plot, reaching a slope of O.1 in about 50 ha. No other model of community structure can make such a precise prediction. 5 The results demonstrate that diversity studies based on different stem diameters can be compared by sampling identical numbers of stems. Moreover, they indicate that stem counts < 1000 in tropical forests will underestimate the percentage difference in species richness between two diverse sites. Fortunately, standard diversity indices (Fisher's sc, Shannon-Wiener) captured diversity differences in small stem samples more effectively than raw species richness, but both were sample size dependent. Two nonparametric richness estimators (Chao. jackknife) performed poorly, greatly underestimating true species richness.

A time-course study of shoot development in Smilacina racemosa was combined with an analysis of the vascular anatomy to investigate how adjacent sympodial units in the perennial rhizome are structurally related to one another. Organogenesis is seasonal and occurs over a period of 20 mo; leaves and flowers are preformed in miniature 8-12 mo before they fully expand. One lateral bud on the horizontal rhizome is initiated eccentric of the normal plane of distichy toward the lower side of the stem and develops as the renewal shoot. The vascular connection between the renewal shoot and the parent axis is complete; all but 2% of the central bundles of the parent axis directly enter or branch into the renewal shoot. Two features contribute to the completeness of the connection: (1) increased anastomoses of vascular bundles within the branch junction, and (2) the development of special girdling bundles that attach circumferentially to the parent axis. The vascular supply of dormant lateral buds is incomplete; roo...

A new species of Maianthemum (Liliaceae) was discovered in a tropical montane bog at an elevation of 2,500 m in central Costa Rica. The leaf bearing stems and inflorescences are supported by a stiff, erect, branching sympodium that consists of the persistent lower portions of older shoots. This lower portion corresponds in morphology and anatomy to the horizontal subterranean rhizome that is characteristic of all previously described species of Maianthemum. An erect woody habit is rare in the Lily family; an upright aerial rhizome is unique within the

Theories accounting for the maintenance of high tree diversity in tropical rain forests range from those proposing that tropical trees are highly co-evolved niche specialists, to those proposing that they are mostly generalist, undergoing random drift. We test these hypotheses at a meaningful, community-wide scale using data on the spatial patterns and habitat preferences of all species of Aporosa (Euphorbiaceae) growing on two large rain forest plots in Malaysia. Second-order spatial pattern analyses using a method based on Ripley's K function showed that Aporosa species formed spatially distinct assemblages, and a randomization procedure suggested that these assemblages were explained by biases in their distributions in relation to habitat types. Soil type, as determined by parent material, was an important determinant of habitat preferences, although topography and forest structure also accounted for some variation. We conclude that niche differentiation is an important mechanism contributing to the coexistence of Aporosa species at the community scale. However, spatial separation due to these differential habitat biases accounted for only a portion of the high species richness observed in this genus, so other mechanisms must also be sought to account fully for the maintenance of tropical tree species richness.