Dynamics and species richness of tropical rain forests.

Abstract

We present a worldwide analysis of humid tropical forest dynamics and tree species richness. New tree mortality, recruitment, and species richness data include the most dynamic and diverse mature tropical forests known. Twenty-five sites show a strong tendency for the most speciesrich forests to be dynamic and aseasonal. Mean annual tree mortality and recruitment-turnover-is the most predictive factor ofspecies richness, implying that small-scale disturbance helps regulate tropical forest diversity. Turnover rates are also closely related to the amount of basal area turnover in mature tropical forests. Therefore the contribution of small-scale disturbance to maintaing tropical forest diversity may ultimately be driven by ecosystem productivity.The inverse relationship of species richness with latitude has long attracted ecologists' interest. Some explanations concentrate on the evolutionary origins ofhigh tropical diversity; others focus on its maintenance. High community and regional diversity in the tropics has been linked to available energy (1-3), species-specific predation (4), and delayed competitive exclusion (5-7). Yet, the existence of major differences in species richness among tropical forests, of similar theoretical interest, has only recently been well documented (8)(9)(10)(11)(12).Several hypotheses link tree diversity to disturbance at varying spatial and temporal scales. Frequency-or densitydependent mortality may enhance diversity (13). Locally unpredictable disturbance may counteract the effects of pairwise, predictable competitive displacement (7). Environmental contrasts within and among tree-fall gaps may favor trees with different regeneration requirements (14,15 (17) demonstrated density-dependent mortality affecting the most abundant tree species in Barro Colorado Island, Panama. Yet, few coincident data on tropical forest species richness and turnover have been reported, hindering biome-wide evaluation of the dynamics-diversity relationship. In this paper we show that variation in tree species richness among tropical forests not subject to largescale natural disturbances is related to their dynamism, defined as the mean rate of mortality and recruitment, which in turn is related to productivity. We hypothesize that productivity ultimately drives long-term ecosystem dynamics in mature tropical forests, since the faster a forest grows the more rapid stem turnover must be, as long as total biomass is capped by constraining factors. Therefore, high productivity may help maintain exceptional species richness through promoting frequent, spatially unpredictable small-scale disturbance. METHODSWe investigate dynamics and species richness at 25 mature forests from all major tropical regions. Original data come from Peru and Sarawak, where trees -10 cm in diameter at breast height (d.b.h.) were identified, with additional data from the literature and colleagues

An analysis of the floristic composition and diversity of Amazonian forests including those of the Guiana Shield

“…But the signals are also confusing. Phillips et al (1994) did not find a strong link between rainfall and diversity, allegedly, because they did not include the climatic extremes (Clinebell et al 1995). Because probably 90% of the neotropical rain forests do not occur near 'climatic extremes', it appears that the model, as proposed by Clinebell et al (1995), in which annual rainfall and periodicity are the most important factors, may not be sufficient in predicting species diversity over major areas of Amazonia (as will be further shown below).…”

“…In western Amazonia, species richness is strongly correlated with total annual rainfall (Gentry 1988a,b), which is often considered a proximate estimate of ecosystem productivity (Clinebell et al 1995, Gentry 1988aPhillips et al 1994). Rainfall shows a stronger correlation with species richness than do soil fertility and soil toxicity factors (Clinebell et al 1995).…”

“…Until now most studies examining the patterns of plant diversity in the neotropics have also relied heavily on plots in western Amazonia (Clinebell et al 1995, Gentry 1988aGivnish 1999, Phillips et al 1994. In western Amazonia, species richness is strongly correlated with total annual rainfall (Gentry 1988a,b), which is often considered a proximate estimate of ecosystem productivity (Clinebell et al 1995, Gentry 1988aPhillips et al 1994).…”

“…We use one proxy estimate for productivity, rainfall (e.g. Clinebell et al 1995, Gentry 1988aPhillips et al 1994), which shows good correlation with modelled net primary productivity (Raich et al 1991). We analysed the relationship between alpha-diversity and rainfall for the complete data set (including low rainfall plots) and various subsets, based on region, edaphic condition and major soil type with regression analysis.…”

Photosynthesis and carbon gain under contrasting light levels in seedlings of a pioneer and a climax tree from a Brazilian Semideciduous Tropical Forest

“…There is a lack of information on the species of Tropical Semideciduous Forests. Whilst in rainforests rainfall ranges from 2000 to 4000 mm per year (Chazdon 1986, Phillips et al 1994 or even more (Holdridge 1967), in the semideciduous forests the values are between 1000 to 2000 mm (Holdridge 1967, Hogan et al 1995, Morellato & Leitão-Filho 1995, Oliveira-Filho & Fontes 2000. Moreover, the climate of semideciduous forests is characterized by two distinct seasons, a wet and hot and a dry and cold one.…”