Shrub Expansion in SW Greenland Under Modest Regional Warming: Disentangling Effects of Human Disturbance and Grazing

Abstract Shrubexpansion has been observed widely in tundraareas across the Arctic. This phenomenon has been partially attributed to increasing temperatures over the past century. However, relationships among shrubexpansion, grazing, and human disturbance have been studied little. SW Greenland is a subarctic to low-arctic region with a long and complex land-use history and only modest temperature increases over the past 50 years (0.2 °C decade-1), but changes in shrubcover have not previously been studied in this region. We compiled historical photographs of vegetation in SW Greenland (1898–1974) and repeated the photos in 2010 and 2011. Sixty-four photo pairs were cropped into 133 smaller units and classified by aspect, substrate stability, muskoxen grazing, and human disturbance. The photo material was evaluated by 22 experts with respect to changes in shrubcover, revealing a general increase across the whole data set, and in a subset including only undisturbed sites. Shrubcover increased most on E...