This research addresses the cause and effects of western hemlock looper outbreaks in coastal forests of BC. Large-scale outbreaks of western hemlock looper are predicted to become more frequent in coastal forests (Edmonds et al. 1999). Climate and susceptibility of forests are two primary factors underlying this prediction. Simulations of the Canadian Global Climate Model predict drier and warmer summers for coastal BC (Hengeveld 2000). New evidence indicates the onset of western hemlock looper outbreaks in coastal forests are driven by hot, dry summers (McCloskey and Daniels unpublished). Therefore, we may anticipate more frequent outbreaks of western hemlock looper in the CWH zone as climate changes. The frequency of outbreaks may be mitigated or enhanced by the abundance of forests that are susceptible to defoliation. Traditionally, mature and old-growth western hemlock-dominated forests were considered most susceptible to outbreaks (Pacific Forestry Centre 1995, Acres et al. 1999). However, during the 2000-3 outbreak in the Coquitlam River watershed, second growth stands that were 80 to 100 years old were impacted most severely (Burleigh and Gustafsson 2003). Given the prevalence of hemlock-dominated second growth forests in coastal BC, outbreaks of western hemlock looper in coastal forests of BC are likely to become more frequent and widespread in future. In coastal BC, the qualitative impacts of western hemlock looper are well known but they are poorly quantified, which limits our ability to predict with certainty the specific effects of outbreaks. For example, defoliation reduces growth and increase mortality of host trees, altering forest composition and structure often with significant impacts on timber volumes and wildlife habitat (Alfaro et al. 1999). Traditionally, all defoliated stands were "salvaged" or logged in attempt to eradicate the insects and reduce timber losses. As a result, few sites that were defoliated during the past 100 years remain intact today and little is known about the effects of defoliation and recovery of stands after defoliation. Currently, we can make only general statements about when, where, and how much timber may be damaged or lost as a result of defoliation. Given these gaps in knowledge, our primary research objectives are as follows: 1. Identify the climate conditions that triggered outbreaks of western hemlock looper 2. Quantify the impacts of western hemlock looper on tree growth, mortality, composition and structure of coastal forests before, during and after an outbreak 3. Reconstruct western hemlock looper outbreaks to determine historical frequency and test for climate conditions associated with outbreaks Part 1 of the project is complete and Research for part 2 has been subdivided into two studies - a spatial comparison and a temporal comparison. Two thesis chapters and manuscripts are in preparation and will be completed and circulated to research committee members in March 2007. Lab and data analyses for Part 3 are underway. McCloskeys thesis will be complete by June 2007 with a defense tentatively scheduled for August 2007.
McCloskey, Shane P.J., Daniels, Lori D.; McLean, John. 2008. Climate and Outbreaks of Western Hemlock Looper in Coastal Forests of British Columbia. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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