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.
Importance of Demographic Niches to Tree Diversity Condit, Richard; Ashton, Peter; Bunyavejchewin, Sarayudh ...
Science (American Association for the Advancement of Science),
07/2006, Volume:
313, Issue:
5783
Journal Article
Peer reviewed
Open access
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.
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.
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.
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 old‐growth 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.
1 Horizontal and vertical heterogeneity of resource availability, coupled with the specialized use of resources by tree species, results in complex patterns of tree species distributions in tropical ...rain forests. We studied the horizontal and vertical distributions of 4014 individuals in 11 species of early successional Macaranga (Euphorbiaceae) in tropical rain forest in Sarawak, Malaysia. 2 The horizontal distribution of individual trees was assessed with respect to crown light levels, establishment microsites, and broader scale variation in soil textural properties. Vertical distribution was assessed using an allometric approach to estimate maximum tree height (Hmax) and the slope of the sapling height-diameter relationship. 3 Average light levels intercepted and the proportion of individuals in each of five crown illumination classes varied significantly among the 11 species. Species ranged from extremely high-light demanding, to quite shade tolerant. Average light levels intercepted by trees generally increased through ontogeny, but the ranking of species did not change significantly. 4 Fewer individuals of the more shade-tolerant species established on disturbed microsites, irrespective of light levels. Among the more high-light demanding species, the proportion of trees on different types of disturbed sites varied. 5 Trees of seven species were significantly more common on clay-rich soils, two preferred sand-rich soils, and two were not strongly affected by soil texture. 6 Hmaxranged from 5.5 to 31.3 m and was negatively correlated with shade tolerance among species, although among the more high-light demanding species there was a wide range of tree sizes. Among species, Hmaxwas negatively correlated with both the slope and y-intercept of the sapling height-diameter relationship, indicating that small-statured species (also more shade tolerant) had more slender saplings than larger statured species. 7 Heterogeneity of resource availability leads to differences in horizontal and vertical tree distribution, which are important for the coexistence of 11 Macaranga species.
A major floristic and climatic transition from aseasonal to seasonal evergreen tropical forest (the Kangar-Pattani Line; KPL) exists in the Indo-Sundaic region of Southeast Asia. Mechanisms ...constraining species distribution here are at present poorly understood, but it is hypothesized that species differ in their tolerances of abiotic factors, in particular water availability. Under this hypothesis, we anticipate differences in performance or habitat preferences, or both, of species differing in distribution with respect to the KPL. The aim of this study is to test whether geographical distributions can be used to explain variation in growth, mortality and habitat preferences in co-occurring tree species differing in their distribution in relation to the KPL. Pasoh Forest Reserve, Negeri Sembilan, Malaysia; south of the KPL. All tree species within a 50-ha forest dynamics plot were classified as widespread or southern based upon their distributions in relation to the KPL and as habitat specialists or generalists based on spatial association with soil-based habitat categories. Growth and mortality rates, variation in growth and mortality with respect to soil type, and levels of habitat association were quantified for species with different geographical distributions. Differences existed in species performance based upon geographical distributions. Specifically, widespread species had lower growth rates than did species restricted to the aseasonal forests. Mortality rates did not differ as a function of geographical distribution. The growth responses of species to soil habitats also diverged, such that differences in performance of widespread species among soil types were more conservative than those of species restricted in their distribution to the aseasonal forests. However, the proportion of species showing positive habitat associations did not differ significantly between widespread and southern species. Distribution-based differences in species performance and response to soil type support the hypothesis that species tolerant of wider climatic variation perform less well in any given environment due to limitations on plasticity. These performance differences provide quantitative evidence of the role of climatic transitions in determining tree species distributions in relation to the Kangar-Pattani Line in the Indo-Malay region. Such differences in performance have important implications for our understanding of biodiversity gradients and responses of Indo-Sundaic forests to climate change.
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
m
2 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 <1000–5000
m
2, while the distributions of
Dipterocarpus and
Vatica saplings and poles were independent of adult trees. In general, saplings and poles were always positively associated with each other. Spatial segregation among species may imply habitat specialization. A torus-translation analysis of habitat association for each of the dipterocarp species revealed both positive and negative species-specific associations. At HKK, most of the dipterocarps’ spatial distributions were independent of each other and there was no evidence of strong spatial segregation among species. The irregular diameter distributions, clumping at large spatial scales, and lack of positive association between juvenile and adult stems suggest that many of the dipterocarps at the 50
ha plot may have established after a large-scale catastrophic disturbance. In the absence of catastrophic disturbance, we hypothesize that the
Hopea and
Anisoptera populations will eventually disappear from the plot because of a lack of suitable recruitment conditions.
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