NDVI patterns and phytomass distribution in the circumpolar Arctic

The Circumpolar Arctic Vegetation Map (CAVM) was used to analyze the distribution of NDVI and phytomass in the Arctic, providing data for understanding arctic vegetation patterns, assessing change, and calibrating models. The dominant trend in the analysis of Normalized Difference Vegetation Index (NDVI) was a decrease from south to north, correlating with bioclimate subzones and vegetation units. NDVI also decreased at higher elevations and with higher substrate pH. In the coldest bioclimate subzone, increased elevation was not correlated with decreased NDVI. In the warmest tundra bioclimate subzone, especially in Alaska, NDVI did not decrease with the first several hundred meters of elevation. NDVI in this subzone varied more by region than by elevation or substrate chemistry, and was lowest in recently glaciated areas such as the Canadian Shield. Phytomass (above-ground plant biomass) was calculated from NDVI using a relationship derived from ground clip-harvest data. Phytomass for the tundra bioclimate subzone was estimated at 2.5 × 1012 kg, with most of this in the warmest subzone, at the lowest elevations, and on acidic substrates.