UBC Theses and Dissertations
Responses of a high Arctic heath to long-term ambient and experimental warming Hudson, James Michael
The Canadian High Arctic has been warming for several decades and is predicted to undergo substantially more warming over the next century. Increased temperatures are expected to alter the composition, structure, and function of Arctic plant communities. To better understand High Arctic tundra responses to climate warming, I conducted longitudinal and experimental studies in a snowbed heath plant community at Alexandra Fiord, Nunavut (79°N). I collected data in 2007 and 2008 and used data previously collected (1981-2006) by others for this project. Responses to ambient warming were measured by using a point-intercept method in permanent plots (1995-2007) and a biomass harvest comparison (1981 to 2008). To quantify responses to experimental warming, I analyzed point‐intercept data (1996, 2000, and 2007) in plots that were passively warmed by open‐top chambers (OTCs) beginning in 1992. Experimental warming increased mean annual temperature by about 1°C from 1992, while ambient warming increased mean annual temperature by > 2.5°C (model-derived). Ambient warming shifted the composition of the community: evergreen shrub and bryophyte cover increased and lichen cover decreased, leading to an increase in total aboveground biomass over time. Also, canopy height increased while species diversity did not change. The experiment did not produce the same responses as ambient warming. Experimental warming did not strongly affect cover, canopy height, or species diversity. Only one response was significant: lichen cover was 4% lower in warmed plots than in controls. In the experimental plots, temporal changes in cover were more frequent and of greater magnitude than changes due to passive warming. It seems that ambient warming has strongly affected community composition and structure in this High Arctic heath while the experimental treatments did not. These findings support the view that only substantial climatic changes will alter these snowbed heath ecosystems. This study provides the first plot-based evidence for the recent pan-Arctic increase in tundra productivity detected by satellite-based remote-sensing and repeat-photography studies. These types of fine-scale, ground-level observations are critical tools for detecting and projecting long‐term community-level responses.
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