Spatial variations in the decay coefficients of forest ecosystems in East and Southeast Asia

Abstract

We assessed spatial variation in the decay coefficients of fine wood litter on the forest floor in four forest formations in East and Southeast Asia. We used a novel approach to incorporate fragmentation loss in the decomposition process within four plots, each several hectares in area. The spatial patterns showed significant correlations with some biotic, edaphic, topographic, and climatic factors. Variation in the lowland tropical rainforest was driven largely by the feeding behaviors of termites. Variation in the hill dipterocarp forest exhibited no clear correlations with topographic parameters due to complementarity of decay activities by fungi and termites through segregation of their habitat between concave and convex sites, respectively. The subtropical rainforest showed variations associated with habitats distinguished by understory communities, reflecting edaphic conditions. Variation in the warm-temperate lucidophyll forest showed a clear negative correlation with slope convexity. The maximum area of spatial autocorrelation for the decay coefficient was used as the unit area for identification of significant relationships between decay coefficients and net primary productivity for aboveground coarse woody organs in terms of spatial variations, except in the subtropical forest plot. The ecological features of the four research plots were assessed based on spatial variation in structural and functional parameters over the unit areas or among the understory communities. Our results imply that 1) the positive correlations between decay coefficients and net primary productivity in two plots in a tropical zone were realized by spatial properties of the death rates of trees being higher or even at sites with higher decay coefficients and 2) the negative correlations in two plots in subtropical and warm-temperate zones were maintained by increasing the death rates on convex sites through frequent disturbance by typhoons. Inter- and intrasite variations in decay coefficients were evaluated using a probability density function of two-dimensional standard normal distributions regressed from data collected in the study area.