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Patterns of diversity in high Arctic snowbed plant communities at Alexandra Fiord, Ellesmere Island, Canada Treberg, Michael Anthony


This study examines the patterns of diversity within three natural snowbeds and one manipulated snowbed at Alexandra Fiord, Ellesmere Island in the Canadian High Arctic. Recent predictions of climate change in the Arctic suggest that not only will temperature increase, but also snowmelt will be earlier leading to a longer growing season. Experimental manipulations of snowmelt were begun in 1992 in a late-lying snowbed in order to determine the response of species to longer and shorter growing seasons. To measure the biomass of each species within the manipulated snowbed without destructively harvesting the vegetation, the point quadrat method of estimating total species area (TSA) was employed. Simple linear regressions of TSA and biomass for each species were constructed and were used to estimate biomass from only TSA data. For most species the variance explained (R²) was very high ranging, from 0.311 to 0.943. When diversity indices were calculated, there was essentially no difference between the values as calculated from real or from estimated biomass. The best fitting relative abundance distribution model for each quadrat was also consistent, regardless of whether actual or estimated biomass was used. Therefore, this method offers an efficient alternative to destructively harvesting a large number of quadrats for relatively simple communities and allows a non-destructive means to follow biomass changes in permanent quadrats over time. Ordination using redundancy analysis (RDA) showed that gradients of biomass, soil pH, moss cover and snow meltdate were found strongly related to the community structure within the natural and manipulated snowbeds. Total quadrat biomass was found to be the most important variable in the RDA at explaining the variation of species data and was significantly related to diversity. All measures of alpha diversity decreased with increasing biomass. When the three natural snowbed communities are included with other arctic communities, a hump shaped relation between species richness and biomass is observed, with a peak in diversity at moderate biomass. These results offer indirect evidence that biological interactions, namely competition, may be important in structuring these high arctic communities. Patterns of alpha diversity within the natural snowbeds were not significantly related to snowmelt, although there were more graminoid species in the earliest melting plots, with the longest growing season, and more forbs species in the last plots to melt. The manipulated snowbed, with snow removal, snow addition and control plots, also had more graminoid species in the plots where snow had been removed. The lowest species richness was found in the snow addition plots while greatest richness was found in the removal plots. However, evenness increased in both the addition and removal plots. This suggests that the graminoid species will likely become more abundant in the short term if the growing season length increases as a result of climate change. The importance of this work is that it is the first evidence that snowmelt changes will alter the structure of arctic communities, although more research is necessary to determine the resultant functional changes that will likely accompany structural changes in these and other arctic tundra ecosystems.

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