The effects of topography and nutrient limitation on the productivity of a Bolivian montane grassland

Background/Question/Methods The fragmentation of steep, tropical montane landscapes due to anthropogenic activity has increased in recent years, and our ability to predict the significance of these disturbances relies upon an understanding the consequences of these activities on the sustainability of these ecosystems. Effective management and conservation practices must be formulated within the context of the biogeochemical constraints generated by current land use, and these constraints have yet to be elucidated. The present study examined the sensitivity of the grasslands to nutrient limitation and the influence of topography on nutrient availability in the tropical montane grasslands of Amboró National Park. Results/Conclusions After two years of fertilization treatments, aboveground production responded only to N amendments. However, by the third year of the fertilization, aboveground productivity was limited by P availability. I assessed the applicability of elemental N: P ratios for identifying nutrient limitation in these grasslands and found foliar N: P ratios in agreement with N limitation followed by P limitation. Production responses to the fertilization treatments were not affected by topography, as these remained constant along the topographical gradient. Although limitation patterns were constant, plant available P varied with topographic position and corresponded to foliar and root P concentrations. These findings demonstrate that these grasslands exhibit transient nutrient limitations following release from grazing and fire suppression. Erosion and landslides here are a common consequence of the steep topography, heavy grazing, and frequent burning. These perturbations drive large soil nutrient losses that result in nutrient-poor “Inceptisol-like” soils while low nutrient availabilities are reflected in the vegetation's low productivity, and low foliar and root nutrient concentrations.