Comparing global models of terrestrial net primary productivity (NPP): global pattern and differentiation by major biomes

Annual and seasonal net primary productivity estimates (NPP) of 15 global m odels across latitudinal zones and biomes are compared. The models simulate d NPP for contemporary climate using common, spatially explicit data sets f or climate, soil texture, and normalized difference vegetation index (NDVI) . Differences among NPP estimates varied over space and time. The largest d ifferences occur during the summer months in boreal forests (50 degrees to 60 degrees N) and during the dry seasons of tropical evergreen forests. Dif ferences in NPP estimates are related to model assumptions about vegetation structure, model parameterizations, and input data sets.