Document: MAT-3-68-13

Interactions between fire and bark beetles in an old growth pine forest.

SANTORO, A.E.* ¹, M.J.LOMBARDERO ¹, M.P.AYRES ¹ and B.D.AYRES ²

Dartmouth College, Hanover, NH 03755, U.S.A. ¹
Great Lakes Institute for Pine Ecosystem Research, Box 520, Colfax, WI, U.S.A. ²

Abstract:
Forest fires have long been a dominant source of ecological disturbance in northern coniferous forests. The pattern and consequence of forest disturbance from fires could be strongly influenced by interactions between pine trees and bark beetles. Creeping ground fires, which are usually nonlethal to mature pine trees, were common in pre-settlement pine forests of the Great Lakes region and are now becoming increasingly common as a management tool. Fires could weaken the physiological defense mechanisms of pine trees, yet it is also possible that fire could reduce the abundance of insect pests. We tested whether the physiological trauma associated with bark scorching can predispose red pines to attack by Ips bark beetles. Experiments included a large scale prescribed fire (> 1000 ha) and experimental scorching of individual trees with a handheld torch. We also located beetle-infested trees inside and outside of the burned area and compared their growth history with paired unattacked trees. Oleoresin flow, the primary defense of pine against bark beetles, declines within the scorched region of the trunk immediately following fire damage, and attacks by Ips bark beetles can begin within hours or days. However, within one month of the fire, there is an inducible increase in the oleoresin flow of burned trees that can restrict tissue loss to the most severely scorched regions of the lower trunk and permit tree survival. This increase in tree defenses corresponds to a two-fold increase in Ips abundance in burned areas. Thus, the probability of tree mortality from Ips is increased by ground fires but is reduced by an apparently adaptive increase in oleoresin synthesis that is induced by the fire. Surprisingly, Ips attacks were not restricted to slow growing trees but included healthy trees both inside and outside the burned area.

Keywords: fire, tree defense, red pine, Scolytidae

This abstract is being presented at: 10:30 AM in session:
Poster Session #12: Disturbance Ecology.