Micro spatial distribution pattern of litterfall and nutrient flux in relation to soil chemical properties in a super wet tropical rain forest plot, West Sumatra, Indonesia

Abstract

The micro spatial distribution of the litterfall and nutrient flux in relation to tree composition and soil chemical properties was investigated within a one-hectare study plot with 115 subplots (10 m × 10 m) in a super wet tropical rain forest in West Sumatra, Indonesia. Litterfall production and its nutrient flux throughout a one-year period were determined using 63 circular litter traps installed in 63 subplots among the 115 subplots. The aim of this study was to qualify the micro spatial distribution of the litterfall production and nutrient flux in relation to tree composition and soil chemical properties among the 63 subplots within the study plot. To characterize the relationship among the micro spatial distribution of the litterfall, nutrient flux and tree composition and/or soil chemical properties, the correlation coefficients and omega index of Iwao (1977) were determined. The mean litterfall was 11.4 Mg ha-1 y-1 and the litterfall varied among the 63 subplots within the range of 7.4 - 16.3 Mg ha-1 y-1. The variations in litterfall were positively correlated (P = 0.01) to tree density and the number of tree species in the subplots. Based on the nutrient contents and the production of leaf litter, the nutrient fluxes in the 63 subplots were calculated, and were found to vary significantly within the subplots as follows: N, 54-140; P, 1.4-4.5; K, 8.8-27.5; Ca, 71-207; Mg, 6.2-17.7; AI, 3.2-26.4; Fe, 0.7-3.5; and S, 6.2-16.4 (kg ha-1y-1). The amount of each nutrient flux was strongly affected by the amount of litterfall production, and was, in turn, positively correlated with tree density and the number of tree species in each subplot. The micro spatial distributions of nutrient flux showed significant positive correlations with the soil chemical properties of total Nand 0.1 M HCl extractable K at the surface (0-5 cm) soil of each subplot. However, for the other major elements such as Ca and Mg, no correlation was shown. The micro spatial tree species diversity, i.e., the number of species per subplot, showed a significant positive correlation to tree density, litterfall production and Nand Ca flux. However, as Kubota et al.(2000) and results in this paper, show, the micro spatial distribution of soil fertility parameters, except for the 0.1 M HCl extractable Fe in topsoil, had a negative correlation to the number of tree species. These results suggest that in this super wet tropical rain forest, tree species diversity with diverse tree nutritional characteristics may contribute to create the diversity of an edaphic niche, rather than increase the soil fertility level through nutrient cycling via litterfall.