Investigating Coquitlam Watershed’s Western Hemlock Looper Outbreaks
Dr Lori Daniels and her team’s research based in the Coquitlam River watershed investigated the causes of western hemlock looper outbreaks and the impacts of defoliation on forest structure and composition. During the 2000-2003 outbreak, the study compared the effects of three different levels of disturbance severity on stands with comparable tree composition, density, age and stand structure.
Results found that the degree of canopy openness increased with disturbance severity and resulted in an increase in understory vascular plant diversity. These alterations to forest structure and composition increase possible future successional pathways and forest heterogeneity in the landscape.
Tree ring analyses successfully detected documented outbreaks in the 20th century and reconstructed four outbreaks over a 135-year period between 1775 and 1910. Tree rings successful at identifying low, moderate and high severity outbreaks, whereas the written record identified only periods of visible defoliation from high severity outbreaks.
The study’s reconstructed outbreaks showed that the frequency of defoliations has not changed significantly over the past 200 years.