The role of land use and topography in the biogeochemisty of tropical montane ecosystems in Amboro National Park, Bolivia

While our understanding of biogeochemical processes in the tropical biome as a whole is incomplete, this is especially true for tropical montane ecosystems. However, we do know that nutrient availability can affect primary production, biodiversity and the response of ecosystem services to land use change in other ecosystems. Thus, while the factors regulating biogeochemical processes in tropical montane ecosystems are not well understood, the likelihood that ecosystem responses to land use change are severely constrained by nitrogen (N) and phosphorus (P) availability in these topographically complex systems is almost certain. In order to address this, we set up six transects with a full-factorial fertilization treatment every 100m in tropical montane grasslands of Amboro National Park Integrated Management Area, Santa Cruz, Bolivia. Each transect spanned the ridge top to valley bottom. After two years of fertilization treatments, there were no significant changes in foliar chemistry or aboveground biomass response to nutrient additions in these tropical montane grasslands. Aboveground biomass, root biomass, and soil available phosphorus varied significantly with topography. However, % carbon (C), % N soil pH, and inorganic N did not vary significantly from ridge top to toe slope. Additionally, available P may be driving C:N:P ratios in this system. Data collected from three transects in a slash and burn field six months after deforestation show nutrient losses comparable to converted and established grasslands (six transects examined). The persistence of these extensive grasslands in this region may be a result of the interaction between the extreme relief of the area and intensive land use. Initial deforestation and subsequent loss through biomass burning and erosion of large nutrient stocks may create extremely nutrient deficient systems that have small potential for restoration or recovery.