HENRY, Greg H. R.; University of British Columbia: Effects of Long-term Experimental Warming on High Arctic Tundra Ecosystems

Warming experiments were established in 1992 in tundra plant communities arrayed along a moisture gradient at a high arctic site on Ellesmere Island. Open-top chambers (1.8 m² constructed of optically-neutral greenhouse fiberglass) passively warm the tundra plots by 1.5-2&deg C on average, mimicking predictions from global circulation models. The responses vary by species and tundra type. In general, early season phenology is faster and growth is greater in the warmed plots, with non-woody species showing the greatest response. However, responses are muted in wet tundra. Net ecosystem CO₂ flux also changed in warmed plots, increasing in mesic plots and decreasing in wet sites. Plant diversity and abundance has increased in warmed plots at all sites, with increasing biomass of non-woody species. Plant C:N ratios have increased in woody species, while remaining unchanged in herbaceous plants. Warming also increased the flux of available N and P in the soils, including organic forms of nitrogen. The implications of these results will be discussed for high arctic tundra ecosystems, especially feedbacks to soil processes, herbivores and the atmosphere.