Factors influencing northern spruce engraver colonization of white spruce slash in interior Alaska

In interior Alaska, increased use of mechanical fuel reduction treatments, increased interests in the use of wood energy systems as alternatives to fossil fuels, and elevated populations of northern spruce engraver, Ips perturbatus (Eichhoff), have raised concerns regarding the impact of this bark beetle to forest resources. We conducted a large-scale field study in 2009-2011 (Study 1) to determine the effects of slash scoring (mechanical by chainsaw versus none), slash distribution (scattered versus decked), and cutting date (spring versus fall) on I. perturbatus colonization of and reproductive performance in white spruce, Picea glauca (Moench) Voss, slash, and to determine the effects of resulting treatments on adjacent levels of tree mortality caused by I. perturbatus. Unfortunately, attack densities were lower than expected, and did not provide for a very robust examination of the effects of these treatments. As a result, we reproduced several aspects of Study 1 in a second study (2011) using a baited design. Higher levels of I. perturbatus attack and emergence occurred on dispersed logs. Attack densities were highest in the dispersed, unscored treatment, and similar to 70% higher than observed in the decked, scored treatment. The scoring of dispersed logs significantly reduced attack densities by similar to 28%, but had no effect in decked treatments or on levels of emergence in either treatment. Higher levels of attack and emergence were observed on the tops of logs as compared to the bottoms of logs. Brood production (i.e., defined here as emergence/attacks) was also greater on the tops of logs compared to the bottoms of logs, suggesting the tops of logs are not only more attractive to I. perturbatus, but confer some advantage to brood development. Lower levels of attack and emergence occurred on small diameter logs. Higher levels of attack and emergence were observed on logs in a shaded fuelbreak (i.e., a more open condition of lower tree density) compared to the adjacent forest. Overall, our research suggests that unlike other works on Ips spp. in the western USA that promote the desiccation of slash to minimize colonization and brood production, I. perturbatus appears regulated by the apparency and accessibility of host material. This finding highlights the importance of developing management guidelines based on local science. A third study found two semiochemicals, trans-conophthorin and verbenone, reduced colonization of slash by I. perturbatus, and therefore holds promise as a tool for managing I. perturbatus populations. The implications of these and other results to the management of I. perturbatus in interior Alaska are discussed.