UBC Theses and Dissertations
Spatial models of plant species richness for British Columbia's Garry oak meadow ecosystem Boag, Angela Elaine
Garry oak meadow ecosystems in British Columbia are fragmented, increasingly degraded, and have been prioritized for conservation. While distribution maps of remnant meadow patches have been developed, the ecological integrity of plant communities in many of these remnants remains unknown. Modeling and mapping ecological integrity could inform conservation prioritization exercises in the region. The primary goal of this thesis was to develop distribution models of native and exotic plant species richness in Garry oak meadow remnants. Secondly, multiple independent datasets were used to analyze the effects of sample size and sampling bias on the accuracy and reliability of resulting predictive maps, which is an active area of research in species distribution modeling. Finally, I investigated whether Terrestrial Ecosystem Mapping (TEM) – a publicly available GIS layer of plant community associations – provided a valid geographical extent over which to map predictions. In Chapter 2, different datasets were found to produce different models of species richness. However, different native richness models produced similar distribution maps, while exotic richness maps based on different datasets were less similar. The incorporation of spatial variables into models did not improve model fit, however significant residual spatial autocorrelation at a broad scale was detected in some cases, suggesting that an important environmental covariate is missing from these models. Examples of potential missing covariates include deer density and disturbance history. Overall, this research demonstrates that multiple independent datasets are very important iii for validating species distribution models, especially in heterogeneous landscapes. Additionally, large sample sizes and sampling broadly across of the area of prediction result in more robust models. The results presented in Chapter 3 suggest that mapping predictions exclusively over Garry oak ecosystem-classified TEM polygons is potentially overly conservative, as species richness of native meadow species was found to be high in other TEM classifications as well. This suggests that Garry oak meadow plant communities do not exist solely in discreet meadow patches, and that they are dispersed throughout other habitat types including Douglas-fir – salal forests.
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