Litter nutrients in tropical secondary forests in response to climate variability

Secondary forests are becoming a more common land use type in the tropics, and their response to climate is important in light of global climate change. The goal of this study was to investigate the effect of climate (rainfall and temperature) on litter nutrient concentrations, ratios, and use efficiencies in a wet, tropical secondary forest.  Litter from four secondary forest stands located in N.E. Costa Rica was examined every two months from October 2000-2005.  This study assesses short, medium, and long-term climate drivers of variation in leaf litter carbon (C), nitrogen (N), and phosphorus (P).  Phosphorus use efficiency (PNUE) increased with annual rainfall, and litter N:P increased after periods of high rainfall four to five months prior to sampling.  However, temperature rather than rainfall was a more important predictor of litter nutrient status.  Litter %N and [P] declined, and C:N increased with elevated maximum temperatures.  Litter C:P increased with high minimum temperatures.  Secondary forest stands varied in their response to climate such that the stand with the coarsest soil texture drove the response to rainfall.  Stands with finer soil texture responded consistently to variations in temperature rather than rainfall.  Increased rainfall and temperatures may have led to nutrient translocation to new biomass, which was manifested in low litter quality after senescence.  Because litter nutrients show a response to both rainfall and temperature on all investigated time scales, we may expect altered P and N cycling in tropical secondary forests as rainfall and temperature regimes shift with global climate change.