Assessing Forest Tree Communities and Assisted Migration Potential in Toronto’s Urban Forest as a Result of Climate Change

Projected climate change in the Toronto, Ontario, Canada area could greatly alter tree composition within the urban forest. Investigating biological change as a result of climate change is complicated due to the variability among climate model outputs and non-climatic influences on local vegetation. This study approaches the issues of composition change in tree species in Toronto through three interdependent studies. The first study is a comparison of Global Climate Models (GCMs) available through the Intergovernmental Panel on Climate Change's Fourth and Fifth Assessment Reports, AR4 and AR5 respectively. Using a performance metric based on how well the GCMs simulate climate relative to observation, GCMs GFDL-CM3, IPSL-CM5A-LR and MPI-ESM-LR were determined to provide the best Canada-wide coverage for annual average temperature and precipitation changes. The second study correlates a series of biologically-relevant climatic variables to tree distributions of 134 North American trees east of the 100th meridian. The geographical absence or presence of a species was correlated to concurrent climate data, creating a species' climate envelope. Using climate projections from an ensemble of the GCMs GFDL-CM3, IPSL-CM5A-LR and MPI-ESM-LR for the year 2050, a suite of statistical regression and machine-learning techniques were used to predict a likelihood of suitability of trees in the Toronto area based on the derived climate envelopes. While the dominant beech-maple communities are largely projected to stay intact, future climate suitability is likely to shift away from conifers and northern hardwoods into more southerly deciduous trees. The third study evaluates using projected tree suitability whether an assisted migration through the translocation of tree species would be effective in the Toronto area. Of particular interest is the increasing climate suitability that likely will be beneficial to Ontario’s Species at Risk trees. However, the conservation of Ontario’s Species at Risk trees cannot be based solely upon projections of climate, a vulnerability assessment conducted in this study indicate that current pest and diseases threats coupled with and the loss of genetic diversity are also cause for concern.Ph.D