An Environmental Normal of Vegetation Vigour for the Northern Great Plains

Normalized difference vegetation index (NDVI) data from the Advanced Very High Resolution Radiometer (AVHRR) sensor on board the National Oceanic and Atmospheric Administration (NOAA) satellites were used to create a spatially detailed baseline of vegetation conditions in the northern Great Plains of North America. An environmental normal of vegetation vigour was created from NDVI means and standard deviations calculated over 22 years for each 10-day period during the growing season. Significant vegetation vigour anomalies-differences from the normal-were subsequently identified and associated with concurrent temperature and precipitation data. Growing season vegetation vigour anomalies were found to be most dependent on weather patterns from the previous spring, and in some cases, from the preceding summer. Regions with the densest and most diverse vegetation covers were impacted the most by temperature and precipitation. Statistically significant increases in vegetation vigour over the 22-year period were measured across the entire study area, with the exception of the vegetation communities with the sparsest ground covers. This increase was matched by a similarly significant rise in annual NDVI variability for all of the phenologies. The changes in vegetative cover leading to the increase in NDVI values may be related to warmer winter temperatures.