Abstract
While topographic variability and land-颅鈥恥se change have been shown to alter nutrient availability in diverse tropical landscapes, the combined effects of these two factors on nitrogen (N) cycling are poorly understood. In all ecosystems, however, it is vital to understand controls on N availability, as N is an element that is commonly associated with nutrient limitation in ecosystems. This study investigated the effects of topographic position and land-颅鈥恈over type on multiple pools and fluxes associated with the N cycle in a heterogeneous wet tropical forest in southwestern Costa Rica. A suite of N cycle metrics were measured across four land-颅鈥恈over types (primary forest, pasture, 10-颅鈥�15 year successional forest, and 25-颅鈥�30 year successional forest), and at two topographic positions (gentle slope ~10掳 and steep slope ~43掳). Six of seven N metrics assessed differed significantly for both topography and forest type, with the exception being 未15N for topographic position and ammonium (NH4+) for land-颅鈥恈over type. Concentrations of N were higher on gentle versus steep slopes across land-颅鈥恈over types, and pastures exhibited the highest N concentration, with N concentrations declining through secondary forest succession. These findings suggest that differences in slope angle, likely associated with聽erosion rates, and anthropogenic land-颅鈥恈over changes that alter forest dynamics and species composition may cause spatial variation in N cycling and availability. This may have important repercussions for our understanding of nutrient availability across聽heterogeneous tropical landscapes that are diverse in both topography and land-颅鈥恈over.