The effect of block composition on the severity of spruce beetle (Dendroctonus rufipennis) damage in northern British Columbia

Abstract

The spruce beetle (Dendroctonus rufipennis) is a natural part of the western North American landscape, feeding on the phloem of trees in the Picea genus. The spruce beetle generally feeds on downed trees but can also feed on standing living trees if beetle populations and host trees are plentiful. If this occurs, it can result in an outbreak of spruce beetle populations. With the help of blue-stain fungi, these outbreaks can cause high mortality in spruce tree populations and devastate forests. Multiple factors can contribute to an outbreak of spruce beetle, with most linked to climate change. The government of British Columbia has a list of management practices to mitigate the effects of the spruce beetle, but prevention remains elusive. It is known that a more diverse tree stand can mitigate severity of insect attacks, most notably for spruce beetle if there are more diverse coniferous species. Here, an assessment of five blocks of forest set for harvest in two different areas with different levels of tree species diversity in the Omineca landscape unit of BC agrees with these results. The two areas in the Omineca landscape unit consisted of the Mischinsinlinka (MIS) area with low tree diversity and the Gaffney (GAF) area with high tree diversity. The MIS area, which had only two prominent tree species on the sites, experienced high amounts of beetle predation. The GAF, with up to four prominent species of trees, had lower amounts of beetle predation. It was also discovered that the correlation between tree diameter at breast height (DBH) and tree height to beetle attack severity is much stronger in the MIS than the GAF. This suggests that damage correlation is strongest in less diverse stands and less so in more diverse stands.