Preliminary hazard rating for forest tent caterpillar in British Columbia

Abstract

Forest tent caterpillar (Malacosoma disstria Hübner) is a major defoliator of hardwoods throughout North America, including aspen (Populus tremuloides Michx.). M. disstria has been a major concern in many parts of Canada for the last two decades, but until recently in British Columbia it was considered an aesthetic concern only. However, with the increasing interest in the cultivation of hardwoods for fibre, and more recently for fuel, this insect could become a major concern in hardwood management. Records of past M. disstria outbreaks in British Columbia were summarized. The locations and intensity of six outbreaks were overlaid on biogeoclimatic units to determine which biogeoclimatic zones have experienced repeated outbreaks of M. disstria. Between 1944 and 2003, M. disstria outbreaks have become larger in extent and longer in duration. Analysis indicated that aspen stands in the Boreal White and Black Spruce (BWBS), SubBoreal Spruce (SBS) and Interior Cedar-Hemlock (ICH) biogeoclimatic zones have been most frequently attacked. In the BWBS zone, most affected areas (93.3%) were defoliated for only one year (lightly). In the SBS and ICH zones, areas attacked by M. disstria tended to be defoliated two or more consecutive years (40.2% and 56.2%, respectively), and had a greater chance of being more severely defoliated than aspen stands in the BWBS zone.

Expected Effects of Climate Change on Forest Disturbance Regimes in British Columbia

“…Hogg (2001) projected that most of the current aspen parkland and even some of the southern boreal forest may consequently be converted into grassland by the middle of the 21 st century. Aspen-dominated forests in BC may be similarly susceptible to increased defoliator activity as temperatures increase over the next century, despite an apparently greater sensitivity to the amount of suitable host (i.e., trembling aspen) found within each biogeoclimatic unit than to any specific climatic attribute of those units (Otvos et al 2010). This is because the Sub-Boreal Spruce and Boreal White and Black Spruce biogeoclimatic zones throughout central and northeastern BC, which have the highest proportion and greatest total coverage of aspen, as well as the highest historical losses to forest tent caterpillar (Otvos et al 2010), are also projected to have some of the greatest increases in temperature.…”