Litter production and litter nutrient concentrations in a fragmented amazonian landscape

Abstract

We analyzed the effects of distance to forest edge and soil texture on fine-litter production and on nutrient concentrations in the leaf fall in an experimentally fragmented landscape in Brazilian Amazonia. Production of fine litter (leaves, twigs <2 cm in diameter, flowers, and fruits) was measured over a 3-yr period. Litter traps were installed in plots located near (<100 m) and far (>250 m) from forest edges, and in clayey or sandy soils. In total, 28 plots were established, with 10 litter traps per plot. Results reveal a significant effect of distance to forest edge on litter production, but no significant effect of soil type or interaction between soil type and edge distance. On average, annual litter production on edge plots exceeded that on the interior plots by 0.68 Mg/ha (9.50 ± 0.23 vs. 8.82 ± 0.14 Mg·ha-1·yr-1, mean ± 1 SE, based on a 3-yr period). With regard to nutrient concentrations in the leaf fall, we detected a significant effect of soil type on three of eight nutrients analyzed. Concentrations of N, Mg, and Mn were greater in leaves on clayey than on sandy soils. Distance to forest edge only significantly affected the concentration of Ca, which was greater near than far from edges, perhaps due to strong Ca mobilization by the roots of pioneer trees. Several factors may account for the observed increase in litterfall near forest edges, including the greater prevalence of winds, increased plant desiccation stress, and higher rates of tree recruitment, especially of pioneer trees, near edges. Elevated rates of litterfall are likely to have cascading effects on the ecology of fragmented forests, affecting the invertebrate fauna, increasing seed and seedling mortality, and causing forest fragments to be more vulnerable to destructive surface fires.