To assess the diversity of tropical tree life histories, a conceptual framework is needed to guide quantitative comparative study of many species. We propose one such framework, which focuses on long-term performance through ontogeny and over the natural range of microsites. For 6 yr we annually evaluated survival, growth, and microsite conditions of six non-pioneer tree species in primary tropical wet forest at the La Selva Biological Station, Costa Rica. The species were: Lecythis amp/a, Hymenolobium mesoamericanum, Dipteryx panamensis, Pithecellobium elegans, Hyeronima alchorneoides (all emergents), and Minquartia guianensis (a canopy species). The study was based on long-term measurement of individuals from all post-seedling size classes. Trees were sampled from 150 ha of primary forest spanning several watersheds and soil types. To evaluate individuals' microsites we recorded the number of overtopping crowns, forest phase (gap, building, mature), and crown illumination index (an estimate of the tree's light environment). For comparison, we also evaluated the microsites of three species that have been categorized as pioneers (Cecropia ins ignis, C. obtusifolia) or high-light demanders (Simarouba amara).For the six species of non-pioneers, mortality rates declined with increasing juvenile size class. As a group, these emergent and canopy trees showed a much lower exponential annual mortality rate (0.44%/yr at> 10 em diameter) than has been found for the La Selva forest as a whole. Growth rates increased with juvenile size class for all six species. As adults (trees > 30 em in diameter), all five emergent species showed substantial annual diameter increments (medians of 5-14 mm/yr). Small saplings and adults of all species had significant year-to-year variation in diameter growth, with much greater growth occurring in the year of lowest rainfall. Passage time analysis suggests that all six species require> 150 yr for growth from small saplings to the canopy.Evaluation of all nine species revealed four patterns of microsite occupancy by juveniles. Among the non-pioneers, one species pair (Lecythis and Minquartia: Group A) was associated with low crown illumination and mature-phase forest in all juvenile stages. For two species (Dipteryx and Hymenolobium: Group B) the smallest saplings were in predominantly low-light, mature-forest sites, but crown illumination and association with gapor building-phase sites increased with juvenile size (Simarouba also showed this pattern). Two species (Pithecel/obium and Hyeronima: Group C) were strongly associated with gap or building phase as small juveniles (~4 em diameter) and again as subcanopy trees(> 10-20 em diameter), but were predominantly in mature-phase sites at intermediate sizes.Juveniles of the two pioneer species (Cecropia: Group D) showed the highest crown illumination and association with gap or building sites.Among the six non-pioneer species, only one aspect of juvenile performance clearly varied according to microsite group. The smallest saplings ( ~ 1 em di...

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Summary0 Do local edaphic factors over short environmental gradients a}ect the distribution and abundance of tree species in tropical rain forests< We addressed this question by examining the responses of tree species to soil type\ topographic position and slope angle in an upland old!growth tropical rain forest landscape in Costa Rica\ Central America[ 1 The study area covered 105 ha of non!swamp old growth and included replicated landscape units such as ridgetop to swale catenas\ small watersheds\ and alluvial terraces[ An existing soils map was re_ned using additional sampling along a regularly spaced grid[ Three soil units were de_ned] residual soils derived from in!place weath! ering of basaltic parent material^old alluvial terrace soils formed by precontemporarỹ ooding^and soils of stream valleys[ A Geographic Information System was used to assign soil type to 1089 post!establishment individuals of nine tree species in a long! term demographic study[ Topographic position and slope angle were measured in the _eld[ 2 Data from 322 regularly spaced sample points were used to generate an expected distribution of edaphic variables\ which was compared with the number of individuals of each species in each edaphic category[ 3 Non!random distributions among soil types were found for seven of the nine species\ with topographic positions for six species\ and with slope angle classes for four species[ 4 The issue of what constitutes an independent sample of establishment was analysed by considering the old!growth character of the landscape and evidence for frequent dispersal among edaphic units[ A re!analysis of species| distributions using only individuals × 3 cm diameter showed that results from the original analyses were robust[ 5 Soil type "residual vs[ old alluvial# was not signi_cantly related to diameter growth[ Three species showed signi_cant di}erences in size class distributions between soil types with increasing diameter[ 6 Tree species in tropical rain forests are frequently non!randomly distributed along relatively short edaphic gradients on upland soils[ Future studies should increase the number of species and spatial scale analysed\ incorporate better analyses of edaphic variables\ and include experiments to identify the ecological processes that generate these non!random distributions[ Keywords] Costa Rica\ soil\ tropical trees\ tropical rain forest Journal of Ecolo`y "0887# 75\ 090Ð001

Tropical rain forests have the highest tree diversity on earth. Nonrandom spatial distributions of these species in relation to edaphic factors could be one mechanism responsible for maintaining this diversity. We examined the prevalence of nonrandom distributions of trees and palms in relation to soil type and topographic position (“edaphic biases”) over a mesoscale (573 ha) old‐growth tropical rain forest (TRF) landscape at the La Selva Biological Station, Costa Rica. All trees and palms ≥10 cm diameter were measured and identified in 1170 circular 0.01‐ha plots centered on an existing 50 × 100 m grid. Topographic position was classified for each plot, and slope and aspect were measured. Soil type data were taken from a previous study (). A total of 5127 trees and palms were identified in 267 species. Detrended Correspondence Analysis and Canonical Correspondence Analysis showed that highly significant edaphic gradients were present, with swamp or highly fertile soils separated from the less fertile, well‐drained upland soils. Species composition remained significantly related to topographic position when soil type was controlled for. The main floristic gradients were still significant when flooded sites were excluded from the analyses. Randomization tests on a weighted preference index were used to examine the relations of individual species to soil types and, within the dominant soil type, to topographic position. Of the 132 species with N ≥ 5 individuals, 33 showed significant associations with soil type. Within the dominant soil type, 13 of 110 analyzable species were nonrandomly associated with one or more topographic positions. For a variety of reasons, including issues relating to sample size and adequate edaphic characterization of landscapes, we suggest that the ∼30% of species shown to be edaphically biased in this study is an underestimate of the true degree of edaphically related distributional biases. To evaluate this hypothesis will require mesoscale vegetation sampling combined with quantitative soil analyses at the same scale in a range of tropical rain forests. If edaphic distributional biases are shown to be common, this suggests that edaphically linked processes leading to differential recruitment are similarly common.

The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher's alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼ 40,000 and ∼ 53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼ 19,000-25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼ 4,500-6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.