This map portrays an estimate of above ground plant biomass for the tundra biome based on trans-Arctic field data and AVHRR NDVI (Raynolds et al. 2012). Aboveground phytomass was sampled on transects along the Arctic bioclimate gradient in North America (1750 km long, 8 locations sampled 2003–2006) and Eurasia (1500 km, 5 locations sampled 2007–2010). The study locations were chosen to represent each of the five Arctic bioclimate subzones as displayed on the Circumpolar Arctic Vegetation Map (CAVM) – from Subzone A in the north where shrubs are absent, mosses and lichens are dominant, and bare ground is common, to Subzone E in the south which is characterized by complete ground cover and abundant dwarf shrubs. NDVI values for each phytomass sampling site were extracted from two different NDVI data sets with different spatial resolutions. The maximum NDVI for the specific year during which the phytomass data were collected for each sampling site was extracted from the 8 km GIMMS3g AVHRR data. The relationship between landscape-level zonal phytomass sampled along the Arctic transects and satellite NDVI values were compared using logarithmic regression (y = 0.383 lnx + 0.994, R2 = 0.94, p < 0.001). A logarithmic equation has been shown to best correlate with phytomass, since NDVI is asymptotically non-linear as it approaches its maximum value of 1 for areas with dense plant cover. The regression equation relating aboveground phytomass to the GIMMS3g data for the years sampled was applied to all pixels within that image to create a map showing the distribution of Arctic phytomass and to calculate an estimate of total Arctic aboveground phytomass.
Raynolds, M. K., D. A. Walker, H. E. Epstein, J. E. Pinzon, and C. J. Tucker. 2012. A new estimate of tundra-biome phytomass from trans-Arctic field data and AVHRR NDVI. Remote Sensing Letters 3:403-411.