Impacts of forest insects and diseases: Significance and measurement

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Abstract
Forest insects and diseases are integral components of the forest ecosystem; complexes of each have coevolved with forest ecotypes and are involved in the dynamic processes of forest establishment, growth, senescence, and mortality. Insects and diseases which feed on, or use trees as substrates for their life processes, affect forest, stands, and even entire forests positively and negatively. These effects are termed impacts. The positive impacts are primarily ecological; negative impacts are those which alter values defined by forest management objectives or public perception. The former have received little attention: the latter have been of major concern since their quantification provides the justification for extensive pest management programs. Concepts of impact are examined with emphasis on those affecting the eight resource elements and four support elements defined as goals and objectives of the National Forest System in the National Forest Management Act of 1976. Positive impacts are less thoroughly reviewed, largely because of the paucity of information available. An attempt is made, however, to examine the positive role of insects and diseases in the forest ecosystem and the effects of pest management activities on them. The base line for the review is September 1972, when over 60 experts from Canada and the U.S. examined the state‐of‐the‐art within the USDA Forest Service, the largest practitioner of pest management and hence the agency most concerned with justification of such activities. Their conclusion: “The Forest Service does not have an adequate system for measuring, evaluating, and predicting insect and disease‐caused impacts on the forest resources of the Nation.” Progress on these tasks is compared with the recommendations made in 1972. Additional recommendations are suggested based on changing concepts and attitudes towards pest management. Significant progress has been made in measurement, evaluation, and prediction of negative impacts — particularly in development of forest growth and yield models, and population and damage models for insects and diseases. Less encouraging is the progress made in monitoring ecological impacts.