Plenty of Trees Left After Pine Beetle Epidemic

Once mountain pine beetles kill off the mature lodgepole pine trees, many sites in central British Columbia should still be well-forested.

Former pine-dominated forests will instead be naturally stocked with other species of mature trees and with young saplings.

But assessments of 122 sites find that not all forests can readily rebound from the beetle epidemic.

Within the Sub-boreal Spruce (SBS) biogeoclimatic zone, ecological conditions vary enough among different subzones to influence a forest's complement of tree species and thus its resilience to beetles. Two SBS subzones, the dry warm (dw) and moist cold (mc), grow a mix of trees that serve to buffer the severity of a pine beetle attack.

In contrast, many parts of the SBS dry cool subzone (SBSdk) could end up with few live trees once the beetles are through. Since lodgepole pine forms over 90 percent of mature SBSdk forests, stands would contain less than 100 mature conifers per hectare after a thorough attack.

In the other two subzones, pine comprises 62 percent of the forest on average, with Douglas-fir, black spruce and hybrid white-Englemann spruce making up the majority of other mature trees. Even if all the pine were to die, these stands would still be considered fully stocked by provincial government standards, averaging 700 trees over 80 years old per hectare.

Nearly all the mixed-species stands also have young trees growing in the understory, amounting to 1170 seedlings and 830 saplings per hectare. The young trees, of which half are spruce and less than one-fifth pine, are also plentiful enough to adequately stock the forest. They equal 15 to 20 years of growth in a new forest.

Meanwhile 40 percent of the areas assessed in the SBSdk lack regeneration. Elsewhere in the subzone, the sparse understory trees are mostly slow-growing pine. Saplings in the mixed stands of the other two subzones average 4.6 m in height, which is 1.3 metres taller than the SBSdk saplings.