Soil‐related performance variation and distributions of tree species in a Bornean rain forest

Abstract

Summary1 Spatial distributions of tropical trees often correlate with environmental variation, suggesting that ecological sorting caused by niche differentiation may be important for maintaining species diversity. 2 Four soil types have been identified in a 52-ha forest dynamics plot in Bornean mixed dipterocarp forest (ranked by increasing fertility and moisture: sandy loam, loam, fine loam, and clay). The distributions of 73% of tree species in the plot are significantly aggregated on one of these soil types. We tested the hypothesis that variation in performance (growth and mortality) underlies these edaphically biased species distributions. 3 Annual growth and mortality rates over 5 years were estimated for trees ≥ 1 cm in diameter and compared among soil types, life histories and species-aggregation patterns. 4 Overall, growth and mortality rates were lowest on the poorest soil (sandy loam). Growth rates on each soil type correlated with soil fertility for pioneers, while mortality rates correlated with soil fertility for both pioneers and late-successional species. 5 There was little evidence that soil specialists had a home-soil performance advantage. Soil-specific ranks of growth and mortality rates of each species-aggregation group largely mirrored the ranks of their rates across the plot and did not shift substantially among soil types. On every soil, species aggregated on sandy loam or clay ranked last or next-to-last, and species aggregated on loam ranked the highest. 6 Ecological sorting of species among soils was strong. With increasing diameter, species were lost from the soils on which they were not aggregated more frequently than would be expected based on random mortality. The underlying mechanisms of ecological sorting may involve low mortality rates as a requirement for species to achieve high abundance on the poorest soil, whereas for the richer soils, having high growth rates appears relatively more important for achieving high abundance. 7 Thus, species' demographic responses to resource variation among soil types, especially related to the poorest soil, affects tree species distribution patterns in this forest and thereby influences the structure of tropical forest communities.

Dispersal Modes and Spatial Patterns of Tree Species in a Tropical Forest in Arunachal Pradesh, Northeast India

“…For example, tree species were found to show demographic responses to variation in soil types which appeared to influence adult tree distributions [55]. Although, we did not measure habitat characteristics, there were habitat differences between plots, with some species represented patchily in a few plots with suitable habitat.…”

Habitat niche partitioning by 16 species of Myristicaceae in Amazonian Ecuador

“…A more comprehensive understanding of habitat-related spatial aggregation in tropical tree communities would require evidence that species have improved growth and/or survival in the habitat in which they are aggregated (e.g. Russo et al 2005).…”

Covariation between understorey light environments and soil resources in Bornean mixed dipterocarp rain forest

“…At Lambir, maximum rates of carbon assimilation are faster on average for tree species that specialize on the sandy loam soil type, compared with clay, which is contrary to expectations based only on soil resource availability (Russo et al 2010). However, the reduced soil resources on sandy loam soil may ultimately limit carbon gain or shift carbon allocation below-ground or to making longer-lived tissues, since juvenile trees on this soil have the slowest diameter growth rates (Russo et al 2005). The fastest diameter growth rates are achieved by trees on the loam and fine loam soils, followed by those on clay (Russo et al 2005), paralleling the differences in PPFD and dynamic irradiance for these three soil types.…”

“…However, the reduced soil resources on sandy loam soil may ultimately limit carbon gain or shift carbon allocation below-ground or to making longer-lived tissues, since juvenile trees on this soil have the slowest diameter growth rates (Russo et al 2005). The fastest diameter growth rates are achieved by trees on the loam and fine loam soils, followed by those on clay (Russo et al 2005), paralleling the differences in PPFD and dynamic irradiance for these three soil types. These patterns suggest that competitive dynamics among juvenile trees may be dominated more by soil resource availability at the resource-poor end of this edaphic gradient and by understorey irradiance at the other end, as would be predicted by Tilman (1988).…”