Plant Community Responses of Alaskan Arctic Tundra After 14 Years of Experimental Warming and Snow Manipulation

Emissions of greenhouse gases are expected to raise global mean temperature over the next century by 1.0- 3.5°C. Global warming trends are amplified at high latitudes because heating converts high-albedo (reflective) ice and snow surfaces to dark absorptive surfaces that absorb more solar energy and transfer it to the atmosphere. Furthermore, scientists have argued that ecological responses to this recent climate change will be complex and varied. For example, the warming of the Alaskan Arctic during the past 150 years has accelerated over the last three decades and is expected to increase vegetation productivity in tundra if shrubs become more abundant. Predicted vegetation changes in arctic tundra, because of climate change, have therefore been based on a warmer climate that is either drier or wetter than at present. In order to investigate how tundra vegetation may respond to increases in temperature and snow cover, we used 1m2 open-topped fiberglass chambers (OTC's) combined with large snow fences to artificially warm and modify winter snow regimes of a series of permanent vegetation plots established in Toolik Lake Field Station, Alaska. Fieldwork consisted in measuring the vegetation growth and height of plant species in these plots using the point-frame method. The snow cover and temperature manipulation was done in two ecosystem types, dry heath tundra and moist tussock tundra. The study sheds light on how the vegetation of these two tundra sites has responded after 14 years into the experiment and focuses in changes is species composition, relative abundance, diversity and canopy height. Preliminary results suggest major changes in vegetation composition in both tundra sites over the 14 year sampling period. Changes were more conspicuous in the moist tussock tundra site, where considerable increases in the abundance of the dominant species Betula nana, Eriophorum vaginatum, Salix pulchra and Carex bigelowii were detected consistently throughout the years. Instead, changes in the dry heath tundra show a recent decrease in the dominance of the species Arctostaphylos alpina and Dryas octopetala and an increase in the abundance of the species Louseleuria procumbens. Changes observed in the moist tundra supports the predictions of shrub/graminoid dominated tundra in a warmer global temperature scenario while changes in the dry heath tundra might suggest successional patterns in vegetation composition.