Approach
Even modest changes in climate may cause substantial increases in the distribution and abundance of many insects and pathogens, including mostly native species, potentially leading to reduced forest productivity or increased tree stress and mortality. Impacts may be exacerbated where site conditions, climate, other stressors, and interactions among these factors increase the vulnerability of forests to these agents. Actions to manipulate the density, structure, or species composition of a forest may reduce susceptibility to some insect pests and pathogens. Assessments that compare topographic features and site conditions can help identify forest stands with higher and lower vulnerabilities, especially for insects and pathogens favored by drought.
Tactics
- Thinning to reduce the density of an insect’s host species in order to discourage infestation, based on the knowledge that species are especially susceptible to insects and pathogens at particular stocking levels.
- Adjusting rotation length in production forestry operations to decrease the period of time that a stand is vulnerable to insect pests and pathogens, based on the knowledge that species are especially susceptible to insects and pathogens at particular ages.
- Creating a diverse mix of forest or community types, age classes, and stand structures to reduce the availability of vulnerable individuals of host species for insects and pathogens.
- Thinning trees to promote wide and irregular spacing and selecting the healthiest trees that include a combination of both vigorous (i.e., fast-growing) and slower-growing trees to reduce the likelihood of insect attack and high stand mortality under outbreak.
- Using insecticides, including the use of anti-aggregate semiochemicals (e.g., use of verbenone for mitigating impacts of mountain pine beetle), as a preventive treatment to protect high-value individual trees from attack in areas of increasing bark beetles.
- Red turpentine beetle impacts can be reduced by limiting the amount of basal burn injury during prescribed fire and by duff raking around high value pines.
- Promptly treating potentially infested green material (“green slash”) from healthy stands by chipping, burning, burying, or removing from the site to a safe location.
- Restricting harvest and transportation of logs near stands already heavily infested with known insects or pathogens.
- Using impact models and monitoring data to anticipate the arrival and spread of insects and pathogens (e.g., goldspotted oak borer, sudden oak death) and prioritize management actions to help limit their spread.
Strategy
Strategy Text
Biological stressors such as insects, pathogens, invasive species, and herbivores can act individually and in concert to amplify the effects of climate change on ecosystems. Forest managers already work to maintain the ability of forests to resist and recover from stressors; as an adaptation strategy, these efforts include an emphasis on anticipating and preventing increased stress before it occurs. Climate change has the potential to add to or intensify the impact of many biological stressors, including forest insects and disease and invasive plant species, which heightens the importance of responding to these issues. Dealing with these existing stressors is a relatively high-benefit, low-risk strategy for climate change adaptation, in part because of the existing body of knowledge about their impacts and the existing collection of solutions.
Swanston, C.W.; Brandt, L.A.; Butler-Leopold, P.R.; Hall, K.R.; Handler, S.D.; Janowiak, M.K.; Merriam, K.; Meyer, M.; Molinari, N.; Schmitt, K.M.; Shannon, P.D.; Smith, J.B.; Wuenschel, A.; Ostoja, S.M 2020. Adaptation Strategies and Approaches for California Forest Ecosystems. USDA California Climate Hub Technical Report CACH-2020-1. Davis, CA: U.S. Department of Agriculture, Climate Hubs. 65 p.