ABSTRACT. The spatial heterogeneity of element fluxes was quantified by measuring litterfall, throughfall and litter decomposition for 1 y in 30 randomly located sampling areas in a lowland dipterocarp rain forest. The idea tested was that turnover of elements is more variable than turnover of dry matter in a forest with extremely high tree species diversity. In spite of the low fertility of the soil (an ultisol), total litter production (leaves, trash, and wood <2 cm in diameter) was high (1105 g m −2 y −1 ) with inputs to the forest floor of carbon, nitrogen, phosphorus, calcium, magnesium, potassium, manganese and iron of 550, 15.3, 0.47, 6.26, 2.49, 4.75, 0.95 and 0.14 g m −2 y −1 respectively. Throughfall was 81% of the annual rainfall and transferred 22.2, 1.37, 0.14, 1.07, 0.67, 0.39, 7.92, <0.06, and <0.06 g m −2 y −1 of organic carbon, nitrogen (all forms), phosphorus, sulphur, calcium, magnesium, potassium, manganese and iron, respectively. Average turnover rates of nutrients in litter were highest for potassium and decreased in the sequence calcium, magnesium, carbon, nitrogen and phosphorus. Concentrations of phosphorus, nitrogen and potassium in litterfall, litter mass and topsoil were closely correlated with each other. Concentrations of calcium and manganese were positively correlated with each other and with elevation. Variations in leaf chemistry and total litterfall caused the spatial heterogeneity of element input to the forest floor to have a coefficient of variation of 30 -70%, depending on the element. Due to the strong positive correlation between element fluxes and pools, the spatial variability of turnover rates (CV c. 20%) was lower than that of element input. Turnover rates for K varied by a factor of 4, and for Ca by a factor of 2.8 when the different sites were compared. The results strongly suggest that the most important factor determining spatial heterogeneity of organic matter and element dynamics on the forest floor is the site-specific amount of leaf fall, rather than spatially variable decomposition rates.

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Effects of tree species heterogeneity on leaf fall were studied in a primary (4 ha) and in a selectively logged forest plot (2.5 ha) in the Ulu Segama Forest Reserve, Sabah, Malaysia, from April 1988 to December 1989. Leaf fall was collected at 30 sampling points in each plot, and identified to species.Dipterocarpaceae, Euphorbiaceae, Lauraceae, Fagaceae and Meliaceae are important tree families in both plots with regard to their contribution to total basal area, tree density and annual leaf fall. The total number of tree species was higher in the primary forest plot (267) than in the logged forest plot (218), although the number of climber species was higher in the logged forest (44) than in the primary forest plot (33). The overlap in species composition between the two forest plots was relatively small (49%) compared with that in family composition (88%).In the primary forest plot, the Dipterocarpaceae contributed 29% of the total basal area and 34% of the annual leaf fall. In the logged forest plot these contributions were much lower, 11% and 15%. The contribution to annual leaf fall made by climbers and pioneer trees was higher in the logged forest plot (34%) than in the primary forest plot (8%).In the primary forest plot, leaf fall was dominated My large emergent and main canopy trees, mainly dipterocarps, and occurred as regular large peaks. In the logged forest leaf fall was dominated by climbers and many, relatively small trees of pioneer species, such as Macaranga hypoleuca, and was more evenly distributed in time.

A two-year study on leaf litter decomposition and litter invertebrates was carried out in a primary (4 ha ( = 4 x 10 4 m 2 )) and logged dipterocarp forest plot (2.5 ha) in the Danum Valley, Sabah, Malaysia. Annual leaf litterfall, leaf litter layer mass and leaf litter decomposition, measured as leaf litter mass loss, were not significantly different between plots. Spatial variation among the 30 replicate sites within each plot was high. Annual rates of total litterfall, leaf litterfall and leaf litter mass loss were 11.5, 6.6 and 6.4 t ha -1 for the primary forest plot and 11.9, 6.2 and 5.5 t ha -1 for the logged forest plot. Rainfall (3000 mm y -1 ) and litterfall were high throughout the year and rates of litterfall and litter disappearance were not related to the pattern of rainfall. In the primary and logged forest, leaf litter layer mass and annual rates of leaf litter disappearance increased with annual leaf litterfall. In the primary forest, the abundance of litter invertebrates increased with mass of leaf litter and fine roots. This invertebrate abundance was higher in the primary forest with a significantly higher abundance of mites, pseudoscorpions and termites. The proportion of mites and pseudoscorpions of the invertebrate fauna was higher in the primary forest; beetles, millipedes and cockcroaches were higher in the logged forest. The most abundant invertebrates were ants, springtails, spiders, woodlice and mites.