ANPP ESTIMATES FROM NDVI FOR THE CENTRAL GRASSLAND REGION OF THE UNITED-STATES

Several studies have suggested the existence of a positive relationshi p between the Normalized Difference Vegetation Index (NDVI) derived fr om AVHRR/NOAA satellite data and either biomass or annual aboveground net primary production (ANPP) for different geographic areas and ecosy stems. We calibrated a 4-yr average of the ingegral of the NDVI (NDVI- I) using spatially aggregated values of ANPP. We also provided an esti mate of the energy conversion efficiency coefficient (epsilon) of Mont eith's equation. This is the first attempt to calibrate a standard NDV I product for temperate perennial grasslands. We found a positive and statistically significant relationship between NDVI-I and ANPP for gra ssland areas with mean annual precipitation between 280 and 1150 mm, a nd mean annual temperature between 4 degrees and 20 degrees C. Dependi ng on the method used to estimate the fraction of photosynthetic activ e radiation, the energy conversion officency coefficient was constant (0.24 g C/MJ), or varied across the precipitation gradient, from 0.10 g C/MJ for the least productive to 0.20 g C/MJ for the most productive sites.