UBC Theses and Dissertations
Effects of long-term experimental warming on three High Arctic plant communities Edwards, Marc
Arctic regions are experiencing faster rates of atmospheric warming than any other biome. Increasing temperatures will affect the biomass, phenology, and composition of Arctic vegetation, which in turn will alter ecosystem functions such as greenhouse gas flux and nutrient cycling. These functional changes are likely to affect feedbacks to terrestrial and atmospheric systems. Responses are expected to occur at a range of scales and are likely to show close coupling to environmental conditions. In this thesis I compare ecosystem response in three plant communities after 18 years of experimental warming on Ellesmere Island, Canada. Warming response was measured at peak season in a dry, mesic and wet community. Biomass, height, and composition were measured using a point-intercept method and CO₂ flux was measured using an infrared gas analyzer and a custom made chamber. Environmental and NDVI data were collected from all three communities as well as being sampled across the entire lowland to map environmental heterogeneity and identify predictors of NDVI. All three plant communities showed structural responses to warming. Total above-ground biomass and height did not show significant changes but growth form composition shifted in all cases. Increases were observed for graminoids and forbs at the dry site; graminoids, deciduous shrubs and bryophytes at the mesic site; and deciduous shrubs and bryophytes at the wet site. Lichen abundance decreased at all sites. CO₂ flux responses were largely explained by compositional changes. All sites were CO₂ sinks at peak season and the dry and wet sites became stronger sinks as a result of warming. Landscape scale mapping successfully displayed the variation in environmental variables and NDVI across the landscape. Soil moisture was identified as an important determinant of NDVI signal and NDVI showed potential as a predictor of CO₂ flux. These results support the prediction that climate change response will be ecosystem specific. While some general trends existed across multiple communities, each community had a unique response to warming. Large scale climate change predictions will have to account for such variability.
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