The central U.S. is an important food and timber-producing region and could potentially be a large-scale carbon sink. These characteristics are functions of the human management of the landscape and favorable soil and climate conditions. Large-scale assessments of carbon uptake and trends in net primary productivity (NPP) have been previously reported for this region using satellite observations, but they unfortunately cannot quantify the contributions from changes in management and technology independently from climate effects. To address this shortcoming, we used the Agro-IBIS dynamic ecosystem model to examine the relationship of temperature and precipitation trends to NPP changes from 1950-2002 and 1982-2002 over both natural and managed ecosystems of the central and eastern U.S. In order to isolate the vegetation growth response to climate trends, we minimized the simulation of management for agroecosystems and forested ecosystems. Simulated NPP trends strengthened between time periods and were positive across most of the domain. For the 1982-2002 period, corn and soybean crops had the largest NPP trend of 4.0 g C m-2 yr-1, followed by deciduous forest and spring wheat with 2.0 and 1.1 g C m-2 yr-1, respectively, while winter wheat had a decreasing NPP trend of -0.64 g C m-2 yr-1 (all p < 0.20). Grassland ecosystems had an NPP trend of 0.76 g C m-2 yr-1 that was not statistically significant, and evergreen needleleaf forest had a negligible NPP trend. Trends in NPP in grasslands, deciduous forests, spring wheat, and winter wheat were associated with increased precipitation, while trends in corn and soybean crops were attributed to a combination of longer growing periods, decreased summer average temperatures, and increased precipitation. We found that 17% of corn and soybean NPP trends could be explained by temperature trends while 35% could be explained by changes in precipitation. Our results provide further evidence supporting observational results that suggest 15-20% of recent crop yield trends can be explained by changing climate, and suggest that over the past several decades, climate changes have favored increased crop productivity in most agroecosystems of the central U.S. with the exception of winter wheat.