Historical and simulated ecosystem carbon dynamics in Ghana: land use, management, and climate

Abstract. We used the General Ensemble biogeochemical Modeling System (GEMS) to simulate responses of natural and managed ecosystems to changes in land use, management, and climate for a forest/savanna transitional zone in central Ghana. Model results show that deforestation for crop production during the last century resulted in a substantial reduction in ecosystem carbon (C) stock from 135.4 Mg C ha−1 in 1900 to 77.0 Mg C ha−1 in 2000, and in soil organic C stock within the top 20 cm of soil from 26.6 Mg C ha−1 to 21.2 Mg C ha−1. If no land use change takes place from 2000 through 2100, low and high climate change scenarios (increase in temperature and decrease in precipitation over time) will result in losses of soil organic C stock by 19% and 25%, respectively. A low nitrogen (N) fertilization rate is the principal constraint on current crop production. An increase in N fertilization under the low climate change scenario would increase crop yield by 14% with 30 kg N ha−1 and by 38% with 60 kg N ha−1, leading to an increase in the average soil C stock by 12% and 29%, respectively, in all cropland by 2100. The results suggest that the climate changes in the future from current climate conditions will not necessarily become a determinant control on ecosystem C fluxes and crop production, while a reasonable N fertilization rate is critical to achieve food security and agricultural sustainability in the study area through the 21st century, and current cropping systems could be optimized to make full use of the rainfall resource.