Effects of Pathogens and Bark Beetles on Forests

Abstract

This chapter addresses the varied roles that root pathogens and bark beetles play in western coniferous forests as (1) regulators of ecological structure and processes, (2) arbiters of management success and (3) agents of significant economic loss. Pathologists, entomologists, and forest managers often speak of the "impact" of fungal and insect "pests" on forest values. This terminology carries connotations of death and destruction that reflect only part of the role that these organisms play in the forest. The death of a tree may represent the loss of many cubic meters of timber, but at the same time, may improve soil fertility and growing conditions for surrounding trees and increase the non-economic diversity value of the forest by promoting non-host vegetation and creating new habitat for cavity-nesting birds and mammals. In most situations, it is impossible to compute a net "impact" because of the mixture of economic and non-economic values and ecological processes involved. We have chosen to avoid this problem by referring to the "effects" of root pathogens and bark beetles on various values and processes. Our goal, in part, is to provide a compilation of both economic and ecological effects of these organisms.