Assessment of nutrient returns in a tropical dry forest after clear-cut without burning.

Tropical dry forests (TDFs) are being deforested at unprecedented rates. The slash/burn/ agriculture/fallow-extensive livestock sequence causes significant nutrient losses and soil degradation. Our aim is to assess nutrient inputs and outputs in a TDF area under an alternative management system, for exclusive wood production. The study involved clear-cutting a preserved caatinga TDF site without burning, quantifying nutrients exported in firewood/ timber and nutrients returned to the soil from the litter layer plus the slash debris, left to decompose unburned on the soil surface. Before clear-cut, the litter layer on the forest floor contained 6.1 t ha of dry matter (DM). After clear-cut, the aboveground biomass was 61.9 t DM ha-1 (consisting of 21.5 t DM ha-1 of commercial wood and 40.4 t DM ha-1 of clear-cut debris that did not include the underlying litter layer). The litter layer was composed of fine and coarse litter, with turnovers of 0.86 and 0.31 year-1, respectively, separately measured in uncut control plots during two rainy seasons (Dec-2007/June-2008 and Dec-2008/ June-2009). In a single season, its decomposition returned to the soil 48.4, 1.16 and 12.3 kg ha-1 of N, P and K. The clear-cut debris was mainly composed of branches, 33.4 t ha-1, bromeliads, 5.63 t ha-1 and green leaves, 1.32 t ha-1. In-situ decomposition rates for branches and bromeliads were 0.24 and 1.47 year-1, respectively. After two rainy seasons the clear-cut debris released 206, 6.5 and 106 kg ha-1 of N, P and K respectively. This input plus that of the underlying litter layer exceeded exports in the commercial wood, and replenished a soil nutrient stock (0?30 cm) of approximately the same magnitude