Sequential patterns of colonization of coarse woody debris by Ips pini (Say) (Coleoptera: Scolytidae) following a major ice storm in Ontario

Abstract

Abstract It is widely known that many bark and wood‐boring beetle species use nonresistant coarse woody debris (CWD) created by disturbances; however, the ability of these secondary species to cause mortality in healthy trees following a build‐up of their populations remains unclear. We characterized the pattern of colonization by Ips pini (Say) following a major ice storm that created large amounts of CWD varying in resistance to colonization (i.e. ranging from snapped tops with no resistance to heavily damaged trees with intact root systems). A major question was how the beetles responded to the different types of storm‐damaged material and whether healthy undamaged trees were colonized and killed following increases in beetle populations. Six red pine, Pinus resinosa Ait., plantations in eastern Ontario were monitored from 1998 to 2001 inclusive: three with high storm damage (approximately 120 m3/ha CWD) and three with minimal damage (approximately 20 m3/ha CWD). Transects (200 × 2 m) were sampled yearly in each plantation to assess the type and amount of damaged pine brood material colonized by the pine engraver beetle, I. pini. Beetles preferentially infested the most nonresistant material available each year (i.e. all snapped tops in year 1, all standing snags, up‐rooted trees and many bent trees by year 2, but still less than 50% of trees blown over but with intact root systems by year 3). By years 3 and 4, the majority (approximately 75%) of severely damaged trees (with > 50% crown loss) died prior to beetle colonization. The size of the beetle population tracked the abundance of available woody material from year‐to‐year within a plantation; populations were very large in the first 2 years, and declined significantly in the last 2 years. Healthy standing red pines were apparently resistant to colonization by the beetles, despite the significant build‐up in their populations. Hence, the results of the present study suggest that native bark beetle populations will not cause further tree mortality following such a disturbance in this region.