Multi-year tree growth responses to Climate Moisture Index Defined Drought Events in Canada

Droughts are events that cause mortality in trees and severely limit growth, but the relationship between drought and mulit-year growth limitation is not yet clearly defined. Therefore, this study aimed to define the effect of drought on tree growth during and after an event. Growth was represented by tree-ring widths from tree-ring database chronologies. The Climate Moisture Index (CMI) was adjusted so values from September to August represented each year and used to represent drought by designating years with a CMI in the bottom 5% of the range for each chronology as drought years. Ring widths were detrended and used to calculate three resilience indices relative to drought years. These three indices were Resistance, Recovery, and, Resilience. Resistance represented drought growth divided by pre-drought growth, Recovery was equal to post-drought growth divided by growth during the drought, and Resilience was calculated by dividing post-drought by pre-drought growth. Post- and pre-drought growth were both considered over a period of 4 years. Index values were stratified by species and ecozone. The results showed a variety of drought responses between each species and ecozone. Species did not have the same kind of response or respond to the same degree in each ecozone. Further analysis should look to remove the effects of other possible confounding factors and separate groups by more distinct areas.