Increased aridity and chronic anthropogenic disturbance reduce litter productivity in a Caatinga dry forest

Abstract

Tropical dry forest productivity is thought to be driven by a combination of natural factors, particularly total water availability and seasonality. However, most of the world’s dry forests have been converted into forest successional mosaics by a combination of slash-and-burn agriculture and exploitation of forest products, which has potential impacts for forest productivity. Here, we examined litter production, nutrient concentrations and fluxes across regenerating and old-growth stands of a Caatinga dry forest during a 48-mo period, assessing the impact of annual rainfall, forest aboveground biomass, soil fertility, forest successional status, stand age and chronic anthropogenic disturbance. We found our sites to have low litter productivity, producing 0.193 ± 0.016 Mg ha−1 yr−1 (mean ± SE) of litter. Moreover, litter production was highly seasonal (> 90% during the dry season), and varied substantially across forest stands (from 0.0035 to 0.564 Mg ha−1 yr−1), but with no differences relative to forest successional status; i.e. similar litter production in regenerating and old-growth stands. Litter production was affected by precipitation, soil fertility and chronic anthropogenic disturbance. Litter nutrient concentration was highly variable across forest stands, but concentration responded very little to our focal drivers. Litter N-concentration was relatively high, while P was very low resulting in a small flux to the soil via litter decomposition. In contrast to litter nutrient concentrations, nutrient fluxes were more predictable, particularly considering forest successional status. Our results suggest that Caatinga dry forest on sandy soils is a low-productivity ecosystem, probably due to a combination of natural and anthropogenic drivers.