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Blue Mountains National Resources Institute

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BMNRI Home > Publications > Search For A Solution > Chapter 9


Publications

Search For A Solution: Sustaining the Land, People, and Economy of the Blue Mountains

Chapter 9: INSECT AND DISEASE FACTORS IN THE BLUE MOUNTAINS

Gregory M. Filip, Torolf R. Torgersen, Catherine A. Parks, Richard R. Mason, and Boyd Wickman


Introduction

Forest health can be defined in several ways but basically implies a resiliency to disturbances caused by various agents, especially insects and disease pathogens. The forests in the Blue Mountains of northeastern Oregon and southeastern Washington are experiencing poor health for several reasons: insect epidemics, drought, overstocking, fire exclusion, selective harvesting, or all of the above. For at least 100 years, forest managers and scientists have been collecting information on populations of these pests in unmanaged, but certainly not natural, forest ecosystems in the Blue Mountains. The forests are "unnatural" because fire has been prevented in areas that, before the turn of the century, had frequent, low-intensity fires that removed the fire-intolerant and pest-susceptible Douglas-fir and true fir. But lack of fire and overstocking of fir are only two of the causes of poor forest health. There are many forests in the interior West that have had similar "no-fire" histories and fir overstocking, yet appear to be in relatively good health. Why? The answer may well involve the population dynamics of forest insects, disease pathogens, and their natural enemies.


The most important pest organisms in the Blue Mountains are the dwarf mistletoes: Douglas-fir dwarf mistletoe (Arceuthobium douglasii), larch dwarf mistletoe (A. laricis), western dwarf mistletoe (A. campylopodum), and lodgepole pine dwarf mistletoe (A. americanum); the stem decay fungi: Indian paint fungus (Echinodontium tinctorium) and annosum stem decay fungus (Heterobasidion annosum); the root disease fungi: Armillaria root disease fungus (Armillaria ostoyae), annosum root disease fungus (H. annosum), laminated root rot fungus (Phellinus weirii), and black stain root disease fungus (Leptographium wageneri); the defoliating insects: western spruce budworm (Choristoneura occidentalis), Douglas-fir tussock moth (Orgyia pseudotsugata), and larch casebearer (Coleophora laricella); and the bark beetles: western pine beetle (Dendroctonus brevicomis), mountain pine beetle (D. ponderosae), Douglas-fir beetle (D. pseudotsugae), spruce beetle (D. rufipennis), fir engraver (Scolytus ventralis), and pine engraver (Ips pini). The economic role that these organisms play in the Blue Mountains is well documented. Their ecological role is not.


In apparently healthy forests of the interior West, pests are present but at levels low enough to cause little or no appreciable damage. Why is this so? Other biological agents termed "natural enemies" help to regulate populations of pest organisms. Important natural enemies of insects and pathogens include other insects and fungi, viruses, bacteria, spiders, birds, and small mammals. Much has been learned about the pest and natural enemy populations in unmanaged stands in the Blue Mountains because of research conducted by entomologists and pathologists, particularly those from the Pacific Northwest Research Station. Critical gaps still occur in our knowledge of pest population dynamics in unmanaged stands.


Many forest practices have been employed in the Blue Mountains for the past 100 years. The most common silvicultural practices include precommercial and commercial thinning, seed tree/shelterwood harvesting, sanitation-salvage harvesting, and clearcutting. Other forest practices that may increase in the future include uneven-age management, prescribed burning, nitrogen fertilizing, stump treatments for root diseases, and aerial application of insecticides. Our knowledge of the effects of these forest practices on insects, pathogens, and their natural enemies has increased, particularly in the last 10 years. Pest population dynamics in unmanaged forest ecosystems are different than in forest ecosystems that have been influenced by various forest practices; the magnitude and direction of these changes are influenced by the type and intensity of the forest practice and the site and stand characteristics. Natural enemies of insects and pathogens are also influenced by forest practices.


Fire and drought are natural events that have shaped the forests of the Blue Mountains for centuries. Yet, our knowledge of the effects of fire (natural and prescribed) and drought on insects, disease pathogens, and their natural enemies in the Blue Mountains is extremely limited. In most cases, we can only draw on research conducted outside the Blue Mountains, frequently in other Western States or sections of North America.


In this synthesis we discuss those factors that affect forest health, especially insects and disease pathogens as influenced by natural enemies, forest practices, fire, and drought, all of which shape the forests of the Blue Mountains as we know them today.


Contents of Chapter Nine:

  • Introduction
  • Pathology Research in Unmanaged Forests
  • Dwarf Mistletoes
  • Stem Decays
  • Root Diseases
  • Other Diseases
  • Entomology Research in Unmanaged Forests
  • Bark Beetles
  • Defoliators
  • Other Insects
  • Natural Enemies of Insects and Disease Pathogens
  • Natural Enemies of Defoliators and Bark Beetles
  • Natural Enemies of Pathogens
  • Effect of Forest Practices on Natural Enemies
  • Monitoring of Natural Enemies
  • Implications of Wildfire and Drought on Insects, Disease Pathogens, and Their Natural Enemies
  • Wildfire and Forest Insects
  • Wildfire and Forest Pathogens
  • Drought and Forest Insects
  • Drought and Forest Pathogens
  • Drought and Natural Enemies of Insects and Pathogens
  • Effects of Forest Practices on Insects and Disease Pathogens
  • Precommericial Thinning
  • Commercial Thinning, Seed Tree and Shelterwood Harvesting
  • Sanitation-Salvage Harvesting
  • Clearcutting and Regeneration
  • Uneven-Age Management
  • Prescribed Burning
  • Stump Treatment for Root Disease
  • Fertilizing
  • Aerial Insecticide Application
  • Monitoring Techniques for Insects and Diseases
  • USFS Forest Pest Management—Permanent Plot System
  • USFS National Forest and Pacific Northwest Research Station Forest Inventory Plot Systems
  • Sampling and Monitoring Techniques for Defoliating Insects

US Forest Service - Pacific Northwest Research Station, Blue Mountains National Resources Institute
Last Modified: Monday, 16 December 2013 at 14:18:43 CST


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