Management tactics to reduce bark beetle impacts in North America and Europe under altered forest and climatic conditions

Of the > 6000 species of bark beetles (Coleoptera: Curculionidae, Scolytinae), ~ 25 species cause significant amounts of tree mortality in conifer-dominated forests. Several tactics are available to manage bark beetle infestations and to reduce associated levels of tree mortality. Suppression involves short-term tactics designed to address current infestations by manipulating beetle populations and typically includes the use of sanitation harvests, insecticides, semiochemicals, or a combination of these and other treatments. Prevention is designed to reduce the probability and severity of future infestations by manipulating stand, forest, and/or landscape conditions by reducing the number of susceptible hosts through thinning, prescribed burning, and/or altering age classes and species compositions. In this chapter, we review the ecology and management of bark beetles in conifer-dominated forests in North America and Europe, where they exert their largest impacts, and provide six case studies focused on the effects of altered forest and climatic conditions on bark beetle ecology and management. We conclude that in many forests bark beetle outbreaks have and will continue to be exacerbated by climate change due to shifts in temperature and precipitation that influence bark beetles, their hosts, and community associates. Changes in forest structure and composition by natural processes and management practices have and will continue to be important factors as well. As a result, natural resource managers will be increasingly challenged to manage bark beetle populations, and to facilitate recovery of landscapes impacted by bark beetle outbreaks. In most cases, current management tactics are based on research and development executed in the 20th century and unable to meet the demands imposed by altered forest and climatic conditions without some modification and/or adaptation.