Warming-Induced Shrub Expansion and Lichen Decline Across the Tuktoyaktuk Coastal Plain

Abstract:

Recent field and remote sensing studies show that shrub expansion has been widespread in low-Arctic ecosystems. However, there are still uncertainties regarding the extent of these changes, the plant functional groups involved, and the relative importance of climate and disturbance as causes of observed changes. Some authors have suggested that shrub expansion may have caused declines in lichens important for caribou forage, but these changes have not been examined at regional scales. Our research on the Tuktoyaktuk Coastal Plain using 30m resolution Landsat satellite imagery from 1985-2011 and high resolution (1:2000) vertical aerial photographs from 1980 and 2013 shows that shrub expansion has been associated with widespread lichen decline . Our analysis shows that the most likely driver of shrub expansion is a 4°C winter temperature increase over the past 30 years, leading to warmer soils and enhanced supply of growth-limiting nutrients. Natural and human-caused disturbances also stimulated increases in shrub cover, but these effects were limited spatially. Our observations are consistent with plot-scale warming experiments showing reductions in lichen cover from shrub growth, and modeling studies predicting large-scale vegetation shifts in the low-Arctic from climate change. These vegetation changes have implications for caribou forage, wildfire regimes, and permafrost conditions.