Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 1 2009 10.5194/bg-6-45-2009 http://www.biogeosciences.net/6/45/2009/ http://www.biogeosciences.net/6/45/2009/bg-6-45-2009.html http://www.biogeosciences.net/6/45/2009/bg-6-45-2009.pdf 45 58 2009-01-08 Historical and simulated ecosystem carbon dynamics in Ghana: land use, management, and climate Z. Tan ztan@usgs.gov L. L. Tieszen E. Tachie-Obeng S. Liu A. M. Dieye SAIC and ARTS, contractors to USGS Earth Resources Observation and Science Center, Sioux Falls, SD 57 198, USA USGS Earth Resources Observation and Science Center, Sioux Falls, SD 57 198, USA Ghana Environmental Protection Agency, Accra, Ghana Geographic Information Science Center of Excellence, South Dakota State University, Brookings, SD 57 007, USA We used the General Ensemble biogeochemical Modeling System (GEMS) to simulate responses of natural and managed ecosystems to changes in land use and land cover, management, and climate for a forest/savanna transitional zone in central Ghana. Model results show that deforestation for crop production during the 20th 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 16% and 20%, 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 lead to an increase in the average crop yield by 21% with 30 kg N ha^−1 and by 42% with 60 kg N ha^−1 (varying with crop species), accordingly, the average soil C stock would decrease by 2% and increase by 17%, in all cropping systems by 2100. The results suggest that a reasonable N fertilization rate is critical to achieve food security and agricultural sustainability in the study area through the 21st century. 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