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ShareMar. 19, 2002 — Edmonton (March 12) - Sustainable Forest Management Network Principal Investigator, Dr. Jens Roland has discovered a correlation between forest tent caterpillar infestations and the amount of forest left standing after an area has been harvested. Says Roland, "In larger forest stands, the mortality factors which cause collapse of the tent caterpillars infestation (parasites and disease) are more effective than they are in small stands." Dr. Roland's work suggests that a forest tent caterpillar outbreak and the rate of collapse is a critical indicator of the overall health of Canada's aspen boreal forest, and provides various new options for forest managers who would like to minimize the effects of forest tent caterpillar outbreaks.
The impact of forest tent caterpillars should not be underestimated. For comparison purposes, at the peak of a caterpillar outbreak, the biomass of caterpillars per km2 would be equivalent to 657 caribou per km2. Similarly, the biomass of the tiny parasitic flies that attack and feed on these caterpillars would be equivalent to 82 wolves in the same one km2 area.
Given the immense scale of the predator-prey battle going in our backyards, parks, and forests, it is not surprising that the forest tent caterpillar is the principal defoliating insect of trembling aspen in the boreal forest across the country. "During a major outbreak," says Roland, "forest tent caterpillars can completely defoliate an aspen forest; virtually stop their growth - reducing growth increment by as much as four cubic metres of wood per hectare each year. "While we can't stop a tent caterpillar infestation," said Roland, "we don't want to do anything to prolong it either, such as rendering its natural enemies ineffective through effects of altered forest structure." If the number of years of defoliation (out of the 12-year cycle) could be reduced by just one year, then fibre production would be increased by almost 10% over-all.
The research also focused on four species of parasitic flies that are the main enemy of these caterpillars and various viral diseases that also kill forest tent caterpillars. Says Roland, "We were aware that forest cover has an impact on the search behaviour of these flies as they attempt to find their prey, and the rate of spread of viruses. The question we needed to answer is-what is the optimum size of this forest cover which allows these agents to operate normally, and to successfully and rapidly suppress an outbreak?"
Roland and his team of researchers sampled 127 sites covering an area of 400 km2 near Ministik Hills, Alberta in aspen stands ranging in six sizes from as small as .28 hectares to 289 hectares. "What we determined," said Roland, "is that for the parasites and the viruses to be most effective, the size of the forest stand should be a minimum of about 100 hectares. Smaller forest stands served as a caterpillar refuge because of less effective natural enemies-helping to extend the length of the infestation by several years."
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