Nunataks and island biogeography in the Alaska-Canada boundary range
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A baseline flora of the nunataks, isolated peaks and ridges protruding above glaciers, is developed for the Juneau Icefield. Nunatak and periglacial sites from adjacent areas in Alaska, northern British Columbia, and the Yukon are included. Key sites are investigated phytosociologically and biogeographically. Species richness is considered in relation to winter low temperature, dominant aspect of the study sites, growing-season length, latitude, elevation, the distance of the sites from the continuously vegetated mainland, and the surface area of the study sites. The nunatak habitats are tested against the tenets of the theory of island biogeography. Though difficult in the time frame of the study (approximately seven years) to draw conclusions on extinction and immigration rates, it is possible to identify species not observed in previous investigations. It is also possible to observe the relationship between richness and nunatak surface area, and richness and the distance of a given nunatak from the continuously vegetated mainland. Surface area of the sites is the variable most correlated with 2 species richness. This finding is in agreement with the theory of island biogeography. Latitude, elevation, and growing-season length are further found to have a strong influence on the richness of the vascular plant assemblages. Species richness has more than doubled from 1948 to 2007, in parallel with a recorded increase in the mean annual temperature of the region over the same time period. The floristic data facilitate monitoring the region for further changes. The geobotany of the northern Alaska-Canada Boundary Range harbors significant information on the past, current and future effects of climate change on sub-Arctic and alpine vegetation.