Arthropod Diversity and Conservation in Old-Growth Northwest Forests

Abstract

Old-growth forests of the Pacific Northwest extend along the coastal region from southern Alaska to northern California and are composed largely of conifer rather than hardwood tree species. Many of these trees achieve great age (500–1,000 yr). Natural succession that follows forest stand destruction normally takes over 100 years to reach the young mature forest stage. This succession may continue on into old-growth for centuries. The changing structural complexity of the forest over time, combined with the many different plant species that characterize succession, results in an array of arthropod habitats. It is estimated that 6,000 arthropod species may be found in such forests—over 3,400 different species are known from a single 6,400 ha site in Oregon. Our knowledge of these species is still rudimentary and much additional work is needed throughout this vast region. Many of these species play critical roles in the dynamics of forest ecosystems. They are important in nutrient cycling, as herbivores, as natural predators and parasites of other arthropod species. This faunal diversity reflects the diversity of the environment and the arthropod complex provides a sensitive barometer of the conditions of the forest. Conservation efforts for forest arthropods are limited at present and controlled largely by land-use policies. For example, an effort is being made to include arthropods in conservation efforts for the Northern Spotted Owl and arthropods will be included in the Forest Health Monitoring program now underway by the U.S. Forest Service. Evidence from other parts of the world suggest that arthropods that depend upon large pieces of dead wood may be particularly threatened by forest management practices. Much remains to be done in the conservation of forest arthropods.