The relationship between NOAA-AVHRR NDVI and ecoregions in Utah

A comparison was made between 3 years of NOAA Advanced Very High Resolution Radiometer (AVHRR) normalized difference vegetation index (NDVI) and an Environmental Protection Agency derived ecoregion map of Utah. NOAA-AVHRR NDVI data representing 61 2-week periods were extracted from the USGS “Conterminous U.S. AVHRR Biweekly Composites” CDs for 1990–1992. An ecoregion map of Utah was extracted from the 1: 7,500,00 “Ecoregions of the United States” database compiled by Omernik (1987). Mean and variance statistics for each 2-week period were compared between ecoregions. With the exception of two Omernik ecoregions, the Colorado Plateau and Northern Basin and Range, yearly mean NDVI values were significantly different. The Colorado Plateau and Northern Basin and Range were significantly different during the latter part of summer and early fall. NDVI variation was found to be a function of interacting climatic, topographic, and latitudinal zonation that influence vegetation growth. These factors also influence ecoregion boundary delineation. Results suggest that ecoregions may be characterized based on phenological variation of vegetation components using NDVI distribution maps as surrogates for vegetation production.