Effects of Bark Beetles Still Evident After 65 Years

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Lodgepole pine forests may never be the same, ecologically, following a mountain pine beetle epidemic. Forests of Banff, Kootenay and Yoho National Parks in the Rocky Mountains, similar to BC’s Montane Spruce biogeoclimatic zone, have become more varied both within stands and across the landscape due to bark beetles.

Understory vegetation initially grows profusely once a beetle outbreak removes more than half the pine overstory. After 25 years, grasses have grown to ten times the volume and dwarf shrubs three times the amount found in forests dominated by older trees.

By 65 years after a beetle infestation, forests look more like those that never saw bark beetles, with moss and common juniper moving into the understory. A key difference though, is that completely new species have established, notably paper birch and Douglas maple. These forests also contain plenty of wood with advanced decay, amounting to 2.5 times the volume found in both younger post-beetle stands and stands unaffected by beetles for the last 150 years.

Sites differ in how long it takes to reforest. At some locations, trees sprouted naturally soon after the epidemic, while for others, new trees took an average of 28 years to regenerate. In forests affected by beetles 65 years ago, the basal area of tree stands has yet to achieve that of a mature forest.

Reference

Pamela R. Dykstra and Tom Braumandl. 2006. Historic Influence of the Mountain Pine Beetle on Stand Dynamics in Canada's Rocky Mountain Parks. Mountain Pine Beetle Initiative Working Paper 2006-15. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria BC. Research Report

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