Indigenous burning, Prescribed Fire, and Goldspotted Oak Borer Management
Principal Investigator: Joelene Tamm
Project Partners: Mark Hoddle, Ph.D.
Institution: University of California Riverside
Project Type: Graduate Student Research
Grant Award: #8GG21811
Amount awarded: $100,000
Award Date: March, 2021
Agrilus auroguttatus, goldspotted oak borer (GSOB), an invasive wood-boring buprestid beetle, has caused widespread oak tree mortality throughout southern California. Beetle larvae feed on cambium under oak bark which causes tree mortality by disrupting water and nutrient transportation. Larvae move to the outer bark to pupate just below the bark surface. This location makes beetle pupae vulnerable to mortality from environmental conditions (e.g., heat) and foraging predators like woodpeckers. The current University of California Extension Office recommended forest treatments are insecticide applications, tree removal, and management of infested wood (e.g., chipping) to kill larvae, pupae, and pre-emergent adult beetles (Flint et al., 2013). These treatments are extremely labor-intensive, cost-prohibitive, and are often implemented on small scale and usually too late to limit the area of infestation. Landscape-scale treatments for GSOB infestations would provide land managers with new management tools to reduce and the slow spread of infestations. However, there are no known efficacious options currently available for use over large areas. Historically, the Indigenous people of California intentionally and periodically burned oak woodlands to improve forest productivity by reducing pest damage, especially losses caused by insects (Anderson 2005; Minnich 1987). Although Indigenous burning practices were outlawed by Mission and Early American governance (Clar 1959), the resurgence of Traditional Ecological Knowledge (TEK) has demonstrated that Indigenous land management practices may have practical large-scale applications for pest management and improving forest health (Hankins et al., 2015). Indigenous burning likely managed insects by removal of pest-infested materials accumulating in forest floor litter. For example, dropped acorns harbor acorn boring pests like Curculio occidentalis and Melissopus latiferreanus, commonly known as filbert weevils and worms. GSOB research shows that seasonal life cycle development can be used to design integrated pest management (IPM) programs to design targeted insecticide treatments on a highly localized scale (Coleman et al., 2015; Havik et al., 2012). Therefore, it may be possible for IPM programs to utilize prescribed fire to manage GSOB infestations, especially in the pupal stage when pupae are residing in pupation chambers close to the bark surface. Historical narrative accounts of indigenous burning, fire ecology research, and yearly conflagrations have led the State of California, to promote programs that reintegrate fire into the landscape to decrease catastrophic wildfire risk and intensity. Since prescribed burning is already being implemented throughout California, we propose that traditional ecological knowledge when combined as part of a prescribed burn program may have the potential as a management tool for managing GSOB infestations over large areas in native California oak woodlands.
The proposed project will assess the effects of heat (kiln studies on firewood) and fire (prescribed burns of oak woodlands) on the potential for management and control of GSOB. Kiln heat treatments of GSOB-infested firewood will determine if it is possible to sterilize oak logs so that they meet commercial phytosanitary requirements. Data from kiln treatment studies will identify minimum lethal temperatures and exposure times for killing GSOB larvae and pupae. Field evaluations of prescribed burns will, in part, assess whether fire temperatures and exposure durations (determined from kiln treatments) are sufficient to kill GSOB larvae and pupae in the outer bark zone of oak trees. The work proposed here aims to develop an Integrated Pest Management program for GSOB (i.e., primarily targeting the pupal stage but with negative impacts likely for eggs and adults).