Arthropod diversity and conservation in old-growth Northwest forests

Old-growth forests of the Pacific Northwest extend along thecoastal region from southern Alaska to northern California and are com-posed largely of conifer rather than hardwood tree species. Many of thesetrees achieve great age (500-1,000 yr). Natural succession that followsforest stand destruction normally takes over 100 years to reach the youngmature forest stage. This succession may continue on into old-growth forcenturies. The changing structural complexity of the forest over time,combined with the many different plant species that characterize succes-sion, results in an array of arthropod habitats. It is estimated that 6,000arthropod species may be found in such forests—over 3,400 differentspecies are known from a single 6,400 ha site in Oregon. Our knowledgeof these species is still rudimentary and much additional work is neededthroughout this vast region. Many of these species play critical roles inthe dynamics of forest ecosystems. They are important in nutrient cycling,as herbivores, as natural predators and parasites of other arthropod spe-cies. This faunal diversity reflects the diversity of the environment andthe arthropod complex provides a sensitive barometer of the conditionsof the forest. Conservation efforts for forest arthropods are limited atpresent and controlled largely by land-use policies. For example, an effortis being made to include arthropods in conservation efforts for the North-ern Spotted Owl and arthropods will be included in the Forest HealthMonitoring program now underway by the U.S. Forest Service. Evidencefrom other parts of the world suggest that arthropods that depend uponlarge pieces of dead wood may be particularly threatened by forest man-agement practices. Much remains to be done in the conservation of forestarthropods.