Response of Ips bark beetles (Coleoptera: Curculionidae: Scolytinae) to prescribed fire in South Carolina

Ips bark beetles (Ips species; Coleoptera: Curculionidae: Scolytinae) play an important role in forest ecosystems by attacking injured, stressed, or dying pine (Pinus) trees. Management of Ips bark beetles has largely focused on prevention by maintaining tree health through silvicultural treatments including thinning to reduce basal area or prescribed fire. However, there is conflicting evidence of whether prescribed fire leads to increased bark beetle populations and, subsequently, increased tree mortality. Recent outbreaks of Ips bark beetles in the southeastern U.S. have caused renewed interest in the interactions between pine management and bark beetle populations. We monitored Ips populations following prescribed fire in intensively managed pine stands and quantified Ips damage. We captured over 361,000 Ips bark beetles with I. avulsus being the most abundant of the three species collected. While we found high variation among Ips populations across study sites and years, there was a significant increase in bark beetle populations after prescribed fire followed by a significant decline the next year. While Ips populations increased up to three-fold after prescribed burns, damage ratings in burned stands were no different than unburned stands which had significantly lower bark beetle populations. Unburned stands had higher basal area and a higher average tree damage rating, but the lowest number of Ips bark beetles. A total of 14,071 facultative (e.g., Monochamus = 9775) and obligate (e.g., Thanasimus dubius = 4296) predators were collected during the study across all sites and the ratio of predators:Ips also significantly increased following prescribed fire. These data suggest that while Ips are ubiquitous and abundant in pine forests being managed with prescribed fire, natural mechanisms such as predator activity mediate their overall damage and impact to southeastern pine stands.