Print PageIn the Pacific Northwestern (PNW) region of North America, climatic conditions have significantly warmed since a predominantly cool phase between 1950-1975. We investigated the implications of this shift in climate on current and future species distributions and the impact on the vulnerability of native tree species. To do so, we first mapped monthly climatic data from 1950 – 2005 at 1 km resolution across the region. The recorded presence and absence of fifteen native tree species from 22,771 field survey plots were then used to establish seasonal limits on photosynthesis and water use using a process-based growth model (3-PG, Physiological Processes to Predict Growth) parameterized for Douglas-fir (Pseudotsuga menziesii), one of the most widely distributed species in the region. Automated decision tree analyses were used to predict the distribution of different species by creating a suite of rules associated with the relative constraints that soil drought, atmospheric humidity deficits, suboptimal and subfreezing temperatures would impose on the growth of Douglas-fir.
Results/Conclusions
We applied these species models annually for the period between 1976 and 2005 to define areas remaining suitable or becoming vulnerable to disturbance based on whether more or less than half of the years fell within the original physiologically defined climatic limits. Based on selection criteria, 70% of the 15 native species of conifers analyzed remained suitably adapted within their original ranges, with 30% deemed vulnerable. Results varied notably by species with western red cedar and western hemlock remaining well adapted, with potential for range expansion in area of up to 50%. In contrast, ponderosa pine, lodgepole pine, grand, and noble fir were classified as vulnerable with potential net contractions in their ranges. The analysis was extended through the rest of the 21st century using climatic projections from the Canadian global circulation model.
