Pacific Northwest Research Station

Technology to Manage Fuel Loads and Reduce Tree Mortality

Economic recovery hirees in this project are field-testing alternative approaches to reduce tree mortality from a combination of sudden oak death (caused by Phytophthora ramorum) and insect attacks. If found to be effective, this technology may provide land managers with a new method for mitigating excessive tree mortality from these organisms. Healthier forests will provide more products, services, and benefits to local communities. Fewer dead trees will reduce the amount of available fuel and lessen the risk of uncontrollable wildfire and its impacts on nearby communities. Individuals hired for these field and laboratory jobs will have the opportunity to advance their knowledge, skills, and training in the field of forest health protection. So far this project has provided employment for two individuals who have since left to accept permanent jobs as forest health specialists. A new employee is anticipated by February 2012.

This project was initiated in late spring 2010 with a search for and selection of suitable study sites in the vicinity of Novato, California (photo 1). The first field experiments were started in September after obtaining the necessary permits from the agencies responsible for managing the sites selected. So far, results from this work have shown that sapwood from within P. ramorum cankers (photos 2, 3, and 4) on stems of coast live oak trees contain much higher concentrations of ethanol than adjacent healthy sapwood outside the canker, or compared to sapwood from nearby healthy trees. The research also demonstrated that traps baited with ethanol lures (photo 5) attract species of bark and ambrosia beetles known to selectively attack inside the boundaries of the P. ramorum cankers and subsequently reduce the trees’ probability of survival. These same beetle species were shown to attack coast live oak logs when sealed holes in their sapwood were filled with ethanol solution. The researchers concluded that ethanol associated with P. ramorum cankers is the primary attractant and attack stimulant for the bark and ambrosia beetles that colonize the cankers and accelerate tree death. Others have reported that preventing beetle attacks could extend the trees’ survival by 5 to 9 years. The trapping experiment described above found that adding either a-pinene or 4-allylanisol to traps baited with ethanol lures greatly reduced the trap catch, indicating that these compounds are repellents. The a-pinene also dramatically reduced beetle attacks on the coast live oak logs with ethanol infused sapwood provided the a-pinene release rate was high enough. This project continues through 2012.