Evaluating the resilience of northern interior cedar hemlock forests to western hemlock looper defoliation events.

Forest response to western hemlock looper (Lambdina fiscellaria spp. lugubrosa) outbreaks in the inland temperate rainforest (ITR) can be quite variable. Sixty-three plots sampled approximately 17 years after collapse of the 1991-94 outbreak east of Prince George, British Columbia, revealed multiple aspects of ecosystem resilience. Overstory recovery appears to be greatest in stands with lower site productivity and in stands with a more severe outbreak history. Forest regeneration is strongly constrained by shrub cover, which is promoted by canopy opennesss and soil nutrients, both of which can be accentuated by defoliators. Shrub cover is more prominent on steep slopes. Site index and soil moisture regime are primarily responsible for niche differentiation among regenerating tree species. While silvicultural intervention may accelerate reforestation on sites dominated by dense shrubs after a looper outbreak, western redcedar (Thuja plicata Donn ex D. Don) can likely achieve full stocking without treatment. Management of defoliated stands for tree production should consider differences in site index, site series, post-outbreak canopy density and annual heat:moisture index among stands. These documented patterns can be mapped and extrapolated throughout the ITR, but forest management options after a defoliation event must be evaluated on a site by site basis. --Leaf i.