Litterfall, Nutrient Cycling, and Nutrient Limitation in Tropical Forests

Patterns of nitrogen, phosphorus, and calcium cycling through litterfall were evaluated using published information from 62 tropical forests. In general, lowland tropical forests have more nitrogen and lower dry mass/nitrogen ratios in litterfall than most temperate forests, while nitrogen return in montane tropical forests is comparable to that in temperate forests. Calcium return is also high in most tropical forests studied, but many tropical forests (lowland and montane) have little phosphorus return and very high dry mass/phosphorus ratios in litterfall compared to most temperate forests. Phosphorus appears to be cycled highly efficiently in such forests. Fine litterfall in the range of tropical forests studied was predicted from climate, and the residuals of this regression were positively correlated with phosphorus but not nitrogen concentrations in litterfall. The amount of fine litterfall (uncorrected for climate) was also significantly correlated with phosphorus concentrations in moist and wet lowland tropical forests. These analyses suggest that phosphorus but not nitrogen availability limits litterfall in a substantial subset of intact tropical forests. Sites on old oxisols and ultisols, especially those in Amazonia, appear to be particularly low in available phosphorus.