| Summary: | Recent global warming, which has been severe in the Arctic, has caused advancement in the timing of snowmelt and expansion of shrubs into open tundra. Such an altered climate may directly and indirectly (via effects on vegetation) affect arctic arthropod populations. I conducted research at four sites in the vicinity of the Arctic Long Term Ecological Research (LTER) site at Toolik Field Station in northern Alaska in the summers of 2010 and 2011 to determine how vegetation and environmental variables affect arthropod abundance, diversity, and phenology (the timing of life history events) in habitats of differing shrub abundance. Shrub-dominated habitats in the Arctic have been shown to capture snow and delay the timing of snow melt, increase light attenuation through increases in canopy cover, and increase structural complexity compared with tundra with low or no shrub abundance. Arthropod abundance, diversity and community composition are known to be strongly influenced by the physical structure of the environment, and the phenology of arctic arthropods has been linked to the timing of snow melt. Consequently, I hypothesized that sites dominated by shrubs create a different habitat than open tundra vegetation and that this would alter arthropod community composition, patterns of abundance, and the phenology of arthropods. Shrub-dominated habitats were found to differ from open tundra habitats in several structural complexity measurements, having greater maximum shrub height, branch complexity, and foliar canopy cover during the period of maximum leaf out; this response was driven by two of the sites that had the tallest shrubs in the study. Additionally, snow melt was delayed in shrub-dominated habitats on average by 4 days, and a corresponding trend toward greater thawing degree days (TDD, more days above freezing) was found in open tundra habitat in 2011. Pitfall traps captured significantly more arthropods in shrub plots than open tundra plots, the most dramatic difference occurring in the most southern ...
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