The post burning response of bark beetles to prescribed burning treatments in Northern California

Ecologists and fire scientists have recommended reintroducing fire to achieve the twin goals of restoring pre-settlement forest conditions and reducing catastrophic fire risk. Prescribed fire is seen as the management tool to help remediate the current problems of poor forest health and extensive high-risk fire behavior characteristics. The accelerated use of prescribed fire in California ecosystems may or may not alleviate these conditions. An increased comprehension of fire-insect interactions is necessary for more effective science based management of forest ecosystems.; Fire may increase the risk of tree mortality from bark beetles by compromising tree defenses against them. Early work by forest entomologists established a direct relationship between fire injury and subsequent insect attack in burned-over areas. Prescribed fires are likely to have a different insect response due to lower fire intensities than wildfires. Fall and spring burns are also likely to have differential effects on trees due to contrasting physiological activity and carbohydrate storage as well as different fuel moisture and resultant fuel consumption levels. This research is designed to test these differences and provide managers with a better understanding of fire-insect interactions with using prescribed burns in Northern California.; This dissertation investigates fall and spring prescribed burns and their role in predisposing trees to bark beetle attack in Northern California. A study of the effects of seasonal understory prescribed burns under a wide variety of stand conditions was conducted during the 1997–2001 time period. Special attention was given to the role of fire in predisposing trees to beetle attack and the effect of fire on the vigor of an individual tree.; Initial concern has centered on the primary tree killers Dendroctonus spp. and Scolytus ventralis Leconte. This research is also finding that Dendroctonus valens, Ips pini, and secondary wood borers are strong contributors to tree mortality with both fall and spring prescribed burns. Phloesinus spp. has been found contributing to small diameter Incense cedar mortality following fall burns. Delayed mortality from bark beetles has been found in both Jeffrey and ponderosa pine up to four years after the initial disturbance. Post-burning bark beetle induced mortality can be quite significant and needs to be managed with the creation of guidelines for estimating the survival of fire damaged trees. The management implications of post-burning bark beetle response are discussed as well as the potential impact of this response on stand dynamics.