With a $100,000 grant from CAL FIRE’s Forest Health Research Program, Joelene Tamm a master's student at UC Riverside and Squaxin Island Tribal member, is partnering with the La Jolla Band of Luiseño Indians to investigate how indigenous cultural burning practices and traditional ecological knowledge can be used to support management of the invasive goldspotted oak borer, an invasive beetle.
Goldspotted oak borer (Agrilus auroguttatus), an invasive tree-killing beetle, has spread rapidly throughout southern California since its accidental introduction in firewood from Arizona 25 years ago, causing the death of 74,000 oak trees. Tamm’s research will develop heat treatment guidelines for infested firewood and inform prescribed fire practices to reduce infestations.
“Goldspotted oak borer is so destructive and hard to kill because it spends most of its time living under the tree’s bark where larvae feed on the vascular system that moves nutrients between the roots and the leaves,” says Tamm. “[Our experiment] seeks to identify a potential heat treatment process that uses lethal temperatures to kill Goldspotted oak borer within firewood. If effective, this practice would make it safe to move firewood from infested areas without the risk of introducing live beetles into new areas.” Preliminary results are promising, with different heat treatments effectively reducing the number of adult beetles that emerge from infested oak firewood by 90 to 100 percent.
With this understanding of heat exposure’s effectiveness, Tamm’s next step is to measure infestation rates in areas with prescribed fires managed using traditional ecological knowledge. Current recommended treatments include insecticides, tree removal, and chipping. These are labor intensive, costly, and often implemented on a small scale or too late to limit infestations. Landscape-scale fire treatments would provide new tools to reduce infestations. This practice will simultaneously improve forest health by reintroducing low-level fire into the ecosystem, something that has been missing for over 100 years.
Indigenous fire practices may offer a low-cost, landscape-level management strategy to reduce goldspotted oak borer populations and promote healthy oak woodland ecosystems throughout tribal, state, federal, county, and private lands.
“Traditional ecological knowledge teaches that Indigenous burning is a caretaker’s responsibility and a landscape stewardship tool that strengthens the human relationships with the land and non-human relatives. Indigenous burning also decreases pest insect populations through removal of dead biomass and provision of fire-derived nutrients that feed and protect the roots, leaves, bark, and acorns of precious oak trees,” says Tamm.