Forest Growth Under Climate Change: How will western Canadian forests respond to rising drought levels?

Trees play a vital role in ecosystems, carbon sequestration, and many industries. Climate change and its associated increase in drought events poses a severe threat to trees, making it essential to understand how drought affects tree growth and survival. This study aims to quantify the differences in growth response to drought of eight tree species in western Canada from 1980 to 2010 and how responses change in different climatic areas. Tree ring width data from two separate databases were detrended to a Ring Width Index (RWI) to highlight annual variations in growth while Climate Moisture Index (CMI) was used to approximate moisture levels. Trees were grouped using k-means clustering of a principle component analysis (PCA) based on annual variability in CMI and RWI. Drought events were determined using vectors representing the relative lowest CMI and RWI values of each year. Resistance (Rs), recovery (Rc), and resilience (Rt) were calculated for each tree based on indicated drought events, and calculated for each species in each cluster. 13 drought events were identified within the study area and time frame. Trees were separated into 10 clusters, where 7 had drought events identified through the PCA. Unexpectedly, many species in each cluster did not have post-drought growth loss. Pinus banksiana in the west-central boreal forest was shown to increase in growth after drought, while Pseudotsuga menziesii had significantly lower recovery after drought under drier average climate conditions. Some clusters followed previously established expectations of moisture limitations in the west-central and southwestern boreal forest, however other clusters in these areas returned to pre-drought growth levels following events. Overall, this study identifies species and areas that will be more vulnerable under future climate conditions, and others that will be more tolerant to lower moisture levels.