GIMMS-NDVI based mapping of the growing season and bioclimatic zones in Fennoscandia and neighbouring parts of NW Russia

The data used in the present study is a 21-year GIMMS-NDVI dataset, surface data on phenology of birch, and temperature data from meteorological stations, all for the period 1982 to 2002. For each pixel a 21-year mean and a mean of peak NDVI value was computed. Threshold values related to this mean, and mean of peak NDVI values, which show the best correlations with the phenological field data were chosen to characterize the growing season. Then time integrated values (TI NDVI) during the growing season were computed to produce a bioclimatological map of Fennoscandia and neighbouring parts of northwestern Russia, which was tested and correlated with growing degree days (GDD) obtained from the meteorological stations. The correlation between GDD and TI NDVI data during the phenologically defined growing season was very high. Therefore, the TI NDVI map could be presented as a bioclimatic map reflecting GDD, except for the areas distorting NDVI values by their strong ground cover heterogeneity.