PARENT SESSION
Contributed Oral Session 79: Forest Ecology: Communities, Species Richness, and Coarse Woody Debris
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 518 A, Level 5, Palais des congrès de Montréal

Soil-related performance variation and species distribution patterns in a Bornean rain forest.

Russo, Sabrina^*,1, Davies, Stuart¹, King, David¹, Tan, Sylvester², ¹ Center for Tropical Forest Science - Arnold Arboretum Asia Program, Cambridge, MA, USA² Sarawak Forestry Corporation, Kuching, Sarawak, Malaysia

ABSTRACT- 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. In a 52-ha forest dynamics plot in Bornean mixed dipterocarp forest, four soil types on a gradient of fertility and moisture have been identified. Previous research found that the distributions of 73% of tree species in the plot were significantly aggregated on one of these soil types. Here, we test the hypothesis that variation in performance (growth and mortality) underlies these edaphically-biased species distributions. Annual growth and per capita mortality rates over 5 years were estimated for trees ≥1 cm in diameter to test whether performance varied among soil types and among soil specialization categories and whether soil specialists have a home soil performance advantage that would lead to ecological sorting of species among soils. Mean growth and mortality rates were lowest on the poorest soil and largely correlated with soil resources. Specialists of the poorest soil had the lowest growth and mortality rates. They maintained above-average growth rates only on their home soil type, but their mortality rates were below average on all soils. Conversely, specialists of richer soils maintained average or above-average growth rates on all soils, but their mortality rates tended to be average or below-average only on richer soils. Ecological sorting of species among soils was substantial. With increasing diameter, species were lost from non-home soil types more frequently than would be expected based on random mortality. Our analyses of performance variation suggest that this ecological sorting may not be a simple consequence of specialists having consistent home-soil performance advantages in terms of both growth and mortality. Low mortality rates may be required 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. Thus, variation in performance among soil types, especially related to the poorest soil, underlies species distribution patterns in this forest and likely influences the structure of tropical forest communities.

Key words: edaphic variation, species distributions, niche differentiation, tree growth and mortality