DIFFERENCES IN VEGETATION COMPOSITION AND STRUCTURE AT GREENING AND NON-GREENING SITES IN THE NORTHWEST TERRITORIES, CANADA

Abstract

Arctic warming is occurring at more than two times the global rate of warming over the past 150 years, which has resulted in widespread vegetation shifts (Post et al., 2009). However, vegetation species are not responding uniformly to rising temperatures. Remote sensing techniques have used the Normalized Difference Vegetation Index (NDVI) to detect changes in vegetation productivity throughout circumpolar Arctic regions. Overall, there has been an increase in vegetation productivity over the past twenty years as warming has increased. Regions which have increased in vegetation productivity are referred to as “greening” regions, whereas regions which have shown no change are referred to as “non-greening” regions. Some regions are showing a decline in productivity, referred to as “browning”. There has, however, been few studies done to ground-validate these changes. Using satellite-derived Enhanced Vegetation Index (EVI) data, a metric that is analogous to NDVI, and a comparison of vegetation height and composition data from ten ‘greening’ regions and ten ‘non-greening’ regions near treeline in the Northwest Territories, these differences were examined at ground-level. Statistical analysis and multivariate ordination were performed to assess significant differences between the two site types, as well as to determine the similarity between sites, and the species that have a tendency to be prevalent in each site type. It was found that greening sites contain more shrub cover. It was also determined that non-greening sites tend to contain more grass/graminoid species as well as non-vascular species and are more variable in terms of species composition and vegetation characteristics than greening sites. This suggests that shrub species are more responsive to warming and have a tendency to be more productive as temperatures increase. This study contributes to a greater understanding of vegetation changes in response to warming at ground-level and can be expanded upon to provide insight into associated faunal range shifts, as well as predict future changes that may occur at treeline as climate continues to warm.