Causes of variation in wood-boring beetle damage in fire-killed black spruce (Picea mariana) forests in the central boreal forest of Quebec

Abstract

Burned trees in the boreal forest are quickly colonized by wood-feeding beetles after fire. Roundheaded and flatheaded borers (Coleoptera: Cerambycidae, Buprestidae) are common wood-feeding beetles whose larvae feed on the phloem in the first instars before entering the xylem, where they excavate galleries several centimetres deep. These organisms cause significant damage to post-fire salvaged wood. Recent studies show that a variety of environmental factors may create heterogeneous patterns of damage throughout burned landscapes. We evaluated the relationship between fire intensity (measured as bole scorch height), tree size, elevation, and the landscape-scale distribution of beetle damage in black spruce in four 2-y-old fires in the central boreal forest of northern Quebec. Beetle damage significantly increased with char height and elevation but not with distance from unburned edge. With regard to tree diameter, the number of entry holes increased with fire intensity for large trees, whereas it declined with intensity for small trees. The most remarkable result was that while a very large sample size enabled us to detect these significant patterns, the difference in predicted beetle attack rates across a wide range of parameter values was quite muted. Thus, managers cannot use these results to dramatically improve either the way in which they salvage or the strategy for set-asides intended to benefit beetles and their subsequent avian predators.