CONSEQUENCES OF HABITAT HETEROGENEITY FOR AVAILABILITY OF NUTRIENTS IN A DRY TROPICAL FOREST

1 This study evaluates the consequences of habitat heterogeneity in te rms of patchy availability of nutrients in a dry tropical forest. The forest floor was characterized by the presence of topographic depressi ons; litter accumulation in these troughs gives rise to patchy microsi tes which are different in appearance from the adjoining non-patchy mi lieu (flats). 2 Litter mass and decomposition were significantly great er in the troughs than in the flats. Decomposition of 95% of the leaf litter needed 488 days in the troughs compared to 576 days in the flat s. 3 Troughs were characterized by higher levels of microbial biomass and available nutrient pool. N-mineralization rates were also higher i n the troughs. C, N and P concentrations in microbial biomass were pos itively correlated with N-mineralization rate when data for flats and troughs were pooled. The study indicated that immobilization and relea se of nutrients occurred in different parts of the year. 4 Fine roots were concentrated in the troughs with the net fine root production of 488 g m(-2) year(-1) compared to 218 g m(-2) year(-1) in the flats. Fi ne root biomass was positively correlated with the concentrations of m ineral N and available P in the troughs. N-mineralization explained 46 -63% variability in fine root biomass in the microsites. 5 The troughs supported greater herbaceous shoot biomass, particularly in the rainy season, thus preventing leaching by immobilizing excess nutrients. He rbaceous shoot biomass was positively correlated with N-mineralization and mineral N throughout the growing season and across the fertility gradient. 6 Troughs, which accumulated litter and trapped the nutrient s in the dynamic microbial biomass, were characterized by higher amoun ts of organic C, total and mineral N, available P and nutrient supply potential. These areas attracted fine roots to support tree growth, co mpensated for nutrient limitation and sustained a fairly high level of net primary production in otherwise nutrient poor, leached, impoveris hed and shallow soil milieu.