PARENT SESSION
Contributed Oral Session 130: Forest Infestations and Mortality
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 514 A, Level 5, Palais des congrès de Montréal
Western hemlock looper populations and the impacts of defoliation on coastal BC forests.
McCloskey, Shane*,1, Daniels, Lori1, 1 Dept. of Geography, Vancouver, BC, Canada
ABSTRACT- Insect herbivory is an essential element of the natural disturbance regime of coastal BC forests. Beginning in 2000, and lasting until 2003, populations of western hemlock looper (Lambdina fiscellaria lugubrosa (Holt.)), reached outbreak proportions within the Coquitlam watershed east of Vancouver, BC, Canada, defoliating approximately 1500 ha of mature hemlock-dominated forest. Outbreaks of this insect have occurred here four times within the past century and surviving trees defoliated during the past outbreaks were located on an isolated island within the watershed. My study examines both the insect population dynamics of the outbreak, including the role of climatic factors in triggering outbreaks, as well as the ecological consequences of the resulting defoliation on tree growth and mortality. I assessed annual survival and mortality of individual trees at varying defoliation severities for 28 sites annually for three years during and following the defoliation event. Overall canopy tree mortality of the sites rose from an average of 25% in the summer of 2002 to 38% in 2003 and 45% in 2004. In the most severely defoliated sites, overall canopy mortality approached 100%. Using dendroecological techniques, a tree-ring signature associated with defoliation of the primary host, western hemlock (Tsuga heterophylla), was identified to determine the impacts of known past defoliations. The associated tree-ring signature displayed three distinct components: lag, suppression, and recovery. The quantification of this signature will permit historical reconstruction of unknown past defoliation episodes, extending the record of western hemlock looper outbreaks by centuries.
Key words: insect outbreaks, dendroecology, distrubance, Lambdina fiscellaria lugubrosa