MECHANISTIC UNDERSTANDING OF BARK BEETLE BEHAVIOR AND PERFORMANCE RESPONSES TO SILVICULTURAL THINNING TREATMENTS
Description of our projects:
It is our interest to provide regionally appropriate data that supports or refutes the conventional wisdom that stand density regulation is the most effective strategy to prevent pine bark beetle damage to Southwestern ponderosa pine forests. This research examines how changes in stand density and composition influence chemical composition of resin and crystallization rate, nutritional quality of phloem, and microclimate. Resin composition and crystallization rate are believed to have direct impacts on beetle reproductive success and survival. Stand composition and density likely affects local climatic patterns, such as wind currents, that would influence beetle flight behavior and host location. Stand density and composition also affect bark and phloem temperature that may influence beetle development and generations per year in multivoltine species. Investigation of microclimate impacts could help clarify if there is an immediate change in stand susceptibility to pine beetle outbreaks after thinning or if changes in susceptibility are long term and rely more heavily on changes in tree vigor. This study will provide strong scientific evidence for or against stand manipulation as a management tool for controlling bark beetles in the ponderosa forests of Northern Arizona.
Implications of the Research:
There is a growing misunderstanding of the effectiveness or lack of effectiveness of silvicultural management of bark beetles, as seen in the recent publication by the Xerces Society on The Science and Myths behind Managing Forest Insect “Pests”. Bark beetles are native forest species and play an important role in decomposition, forest succession, biodiversity and fire-forest relations. However, more importantly, bark beetle outbreaks are occurring in greater frequency and severity over the last ten years than they have in recorded history. The most likely causes for these outbreaks are (1) changes the density and composition of tree species and stands in our National Forests, (2) large scale climatic changes such as extended periods of drought, and (3) a lack of or change in the way we manage pine-forest communities. Simply, the forests that are here today are different than the forests of pre-European settlement, and as a result our present forests are experiences unprecedented pest outbreaks and impacts from both exotic and endemic species.
There is strong evidence that silvicultural methods can and do regulate and prevent the growth of bark beetle populations. For instance, the most effective way (and only true method) to control southern pine beetle outbreaks in the southeast U.S. is to thin and remove both infested trees and trees surrounding infested areas. Silviculatural methods are also effective at controlling mountain pine beetle and spruce bark beetles in areas of the northwest. Although much is known about the effectiveness of thinning and related management methods, we know little about the interface between bark beetles and forest communities in Arizona. This research will provide incite into the variability in resin defenses among ponderosa pines, the effects of stand composition on bark beetle attack behavior and reproduction, and the impacts of microclimate on beetle fitness in stands of various basal area. If thinning is shown to affect bark beetle behavior and reproduction, our results will provide guidelines to improve thinning treatments as a management tool for bark beetles in Northern Arizona.
This research was supported in part by funds by the Rocky Mountain Research Stations, Forest Service, U.S. Department of Agriculture.