ill., maps; Shipping list no.: 90-263-P; "May 1990."; Includes bibliographical references
The Interagency Scientific Committee to Address the Conservation of the Northern Spotted Owl (hereafter the Committee) was established under the authority of an interagency agreement between the, USDA Forest Service, USDI Bureau of Land Management, USDI Fish and Wildlife Service, and USDI National Park Service. The Committee's charter was signed by the agency heads and subsequently incorporated into Section 318 of Public Law 101-121 in October 1989. The Committee was asked to develop a scientifically credible conservation strategy for the northern spotted owl in the United States. Since that time, the Committee has reviewed the literature on the northern spotted owl, heard presentations from most of the scientists doing research on spotted owls, considered the concerns of numerous interest groups, and conducted field trips in Washington, Oregon, and northern California to examine the owl's habitat. We have also interviewed dozens of biologists and land managers. Much of the attention directed toward this bird stems from a growing debate over managing old-growth forests on Federal lands, and from a concern about protecting biodiversity. We understand the significance of these larger issues, but we have kept to our mandate to develop a conservation strategy specifically for the northern spotted owl. We have concluded that the owl is imperiled over significant portions of its range because of continuing losses of habitat from logging and natural disturbances. Current management strategies are inadequate to ensure its viability. Moreover, in some portions of the owl's range, few options for managing habitat remain open, and available alternatives are steadily declining throughout the bird's range. For these reasons, delay in implementing a conservation strategy cannot be justified on the basis of inadequate knowledge. Owl Habitat and The Committee reviewed all available studies dealing with spotted owl habitat, the Population Trends relative abundance of owls related to stand age, and the relative abundance of owls in relation to various proportions of successions growth stages in the general landscape. Habitats selected by northern spotted owls typically exhibit moderate to high canopy closure; a multilayered, multispecies canopy dominated by large overstory trees; a high incidence of large trees with large cavities, broken tops, and other indications of decadence; numerous large snags; heavy accumulations of logs and other woody debris on the forest floor; and considerable open space within and beneath the canopy. These attributes are usually found in old growth, but they are sometimes found in younger forests, especially those that contain remnant large trees or patches of 1 The Conservation Strategy large trees from earlier stands. In younger forests that support breeding owls, the nest and major roost sites are usually found where large trees from the earlier, older stands remain. We evaluated the coastal redwood forests of northwestern California, where numerous owls live in stands that are mostly 50 to 80 years old. We believe their presence is attributable to the region's unique set of conditions, including a rapidly growing tree species that sprouts from stumps; intrusion of other conifer and hardwood species into the understory; relatively high rainfall; a Song growing season; and abundant prey. Under these conditions, the structural attributes that are usually associated with the presence of owls develop at an accelerated rate. We caution strongly against extrapolating these results to other parts of the owl's range. Silvicultural prescriptions might be developed that would yield significant volumes of wood products while maintaining suitable habitat for spotted owls, but we find no clear evidence that such prescriptions currently exist. Until they do, the prudent approach to ensuring the viability of the owl is to protect an adequate distribution and amount of existing habitat. Nonetheless, examining younger forests where spotted owls reproduce successfully should yield valuable insights into silvicultural techniques that could produce both wood products and owls. For at least the past century, loss of spotted owl habitat has exceeded recruitment. By some estimates (perhaps conservative), spotted owl habitat has been reduced by about 60% since 1800. The current total population of the owl is likely to be far less than once existed. The loss of habitat has not been distributed evenly across the range of the subspecies. Owl habitat is also being fragmented, a process that isolates some populations of owls. Fragmentation in the home ranges of individual birds may expose owls to greater risks of predation and competition. It may also result in habitat loss when trees blow down in high winds, and as stands suffer other impacts associated with forest edges. Determining the number of northern spotted owls in existence has drawn considerable attention. Current data do not permit a statistically reliable population estimate. The approximately 2000 pairs located during the past 5 years or reconfirmed from pre-1985 surveys represent an unknown fraction of the total population. More significantly, demographic studies from the Klamath Mountains in California and the Coast Range in Oregon indicate that populations in these study areas are declining. We propose a two-part conservation strategy. The first stage, prescribes and implements the steps needed to protect habitat in amounts and distribution that will adequately ensure the owl's long-term survival. The second stage calls for research and monitoring to test the adequacy of the strategy and to seek ways to produce and sustain suitable owl habitat in managed forests. Insights gained in this second stage can be used to alter or replace habitat conservation areas prescribed in the first stage, but only if the modified strategy can be clearly demonstrated to provide adequately for the long-term viability of the owl. 2 Our strategy largely abandons the current and, we believe, flawed system of one- to three-pair spotted owl habitat areas (SOHAs), in favor of protecting larger blocks of habitat—which we term Habitat Conservation Areas, or HCAs. Large blocks of habitat capable of supporting multiple pairs of owls, and spaced closely enough to facilitate dispersal between blocks, are far more likely to ensure a viable population than the current SOHA system. Owls in an HCA containing multiple pairs will benefit from internal dispersal of juvenile owls as well as recruitment of dispersing birds from other HCAs. Owls in HCAs containing multiple pairs are less vulnerable to random fluctuations in birth and death rates. Large HCAs reduce the impacts of habitat fragmentation and edges, and they are more resistant than SOHAs to small-scale natural disturbances. The Committee has delineated and mapped a network of HCAs necessary to ensure a viable, well-distributed population of owls. Wherever possible, each HCA contains a minimum of 20 pairs of owls. The maximum distance between these HCAs is 12 miles. Our 20-pair criterion is based on models of population persistence and empirical studies of bird populations. We have chosen 12 miles as the maximum distance between HCAs because this value is within the known dispersal distance of about two-thirds of all radio-marked juveniles studied. The HCA concept applies primarily to BLM, FS, and NPS lands, as delineated in the enclosed maps. The Committee strongly recommends that HCAs be established on State lands in certain key areas (as shown on the maps) to assure population connectivity. We also recommend that resource managers of other State lands, tribal lands, other Federal lands, and private lands use forestry and silvicultural techniques and practices that maintain or enhance habitat characteristics associated with spotted owls. In several regions, current habitat conditions and owl densities do not allow us to follow this approach. The Committee has modified the guidelines for these regions. For example, in portions of the Oregon Coast Range, habitat is currently insufficient to fully stock 20-pair HCAs with owls. We have delineated 20-pair HCAs for this area, but they will be not be capable of supporting 20 pairs of owls for many years. In the meantime, individual-pair HCAs are prescribed around all known or future pairs to reach the 20-pair target. A variety of strategies was used in other areas of special concern to help meet the intent of this strategy. Portions of the Cascade Range of northern Washington contain insufficient habitat capable of supporting 20-pair HCAs over the long term because of inherent landscape patterns. In these areas, we delineated a network of smaller HCAs but shortened the maximum distance between them to 7 miles, to facilitate dispersal. In portions of the eastern Cascade Range in Washington and Oregon, and northeast of Mount Shasta in California, relatively little owl habitat exists and spotted owls occur at low densities. We prescribe individual-pair HCAs around all known pairs and pairs located in the future. 3 Spotted owls on the Olympic Peninsula are probably demographically isolated from other populations by more than 60 miles of intensively managed State and private forest lands. We have established a large HCA on National Forest lands, but we also prescribe individual-pair HCAs around all known pairs outside the HCA and recommend smaller HCAs for State lands. Our hope is that connectivity can be restored by using a combination of HCAs and applying innovative silvicultural techniques on State and private lands. Land ownership patterns in the Coast Range of California limit our ability to establish 20-pair HCAs. We have tried to do so wherever possible, but we encourage California to work with private land owners to apply innovative silvicultural techniques to maintain or develop additional owl habitat for dispersal and breeding. We encourage Oregon and Washington to do the same. Logging (including salvage operations) and other silvicultural activities (with the exception of stand regeneration) should cease within HCAs. The Committee recognizes that allowances will have to be made for timber sales already planned and under contract in HCAs, such as sales necessary to meet Section 318 of Public Law 101-121. We considered dedicating corridors of forests between HCAs to facilitate dispersal by juvenile owls, but decided corridors were unnecessary, provided at least 50% of the forest landbase outside of HCAs is maintained in stands of timber with an average d.b.h. of 11 inches or greater and at least 40% canopy closure. We also rely on lands currently allocated to such uses as riparian corridors, streamside management zones, and special management areas for pileated woodpeckers and pine martens to provide additional habitat for dispersing spotted owls. We recommend retaining at least 80 acres of suitable owl habitat around the activity centers of all known pairs of owls in the managed forest, up to a total of seven per township. These centers will serve as older forest nuclei that could become core areas for future breeding pairs of spotted owls as the surrounding forest matures. If healthy populations of northern spotted owls can be sustained in the managed forest, HCAs will no longer be necessary. Timber harvests that affect owl pairs outside the conservation areas are therefore viewed as experiments in managing for spotted owl habitat. Consequences for The Committee believes this conservation strategy, if faithfully implemented, has a the Northern high probability of retaining a viable, well-distributed population of northern spotted Spotted Owl owls over the next 100 years. The HCAs on Federal lands contain 925 known pairs of owls, and we estimate the actual number to be about 1465 pairs. Regeneration of younger stands within HCAs on Federal lands should enable the spotted owl population to increase to about 1759 pairs. These numbers are important, but only up to a point; the amount and spacing of habitat are as critical to the viability of the subspecies as the actual numbers. 4 Implementing the Conservation Strategy Assessment of Impacts Under a worst-case scenario, even with this conservation strategy fully implemented, a short-term loss of a significant portion of the existing population of northern spotted owls is likely. We do not take this loss lightly, but we believe the subspecies can withstand a reduction provided our strategy is followed. Even under the most stringent scenarios of habitat protection, a similar reduction in the number of existing pairs over time seems likely because many pairs of owls live in highly fragmented and marginal habitats isolated from other pairs. Implementing a comprehensive strategy for the spotted owl requires a well-coordinated program of research, monitoring, and habitat management by State and Federal agencies and private landowners. Much room for improvement exists. So far as we can determine, for example, no plans have been made within or among agencies to determine what changes in population size or habitat conditions would trigger a review of, and possible changes in management actions needed to ensure the welfare of the owl. We urge that a coordinator and interagency staff (State and Federal) be assigned to oversee the conduct of the conservation strategy. The coordinating group would have the additional duty of recommending alterations to our conservation strategy. The plan put together by our Committee, however, is a strategy for the entire U.S. range of the northern spotted owl. No part of the strategy was designed to stand alone, and proposed changes must be considered in that light. Our assignment was to develop a scientifically credible conservation strategy for the northern spotted owl. We recognize that the impacts of the strategy we propose will be analyzed by others. The immediate response, we expect, will be to focus almost solely on the short-term economic and social impacts of implementing the strategy as it affects the availability of timber. This assessment is critically important. Adoption of the conservation strategy, however, has significant ramifications for other natural resources, including water quality, fisheries, soils, stream flows, wildlife, biodiversity, and outdoor recreation. All of these aspects must be considered when evaluating the conservation strategy. The issue is more complex than spotted owls and timber supply—it always has been.
The Interagency Scientific Committee to Address the Conservation of the Northern Spotted Owl (hereafter the Committee) was established under the authority of an interagency agreement between the, USDA Forest Service, USDI Bureau of Land Management, USDI Fish and Wildlife Service, and USDI National Park Service. The Committee's charter was signed by the agency heads and subsequently incorporated into Section 318 of Public Law 101-121 in October 1989. The Committee was asked to develop a scientifically credible conservation strategy for the northern spotted owl in the United States. Since that time, the Committee has reviewed the literature on the northern spotted owl, heard presentations from most of the scientists doing research on spotted owls, considered the concerns of numerous interest groups, and conducted field trips in Washington, Oregon, and northern California to examine the owl's habitat. We have also interviewed dozens of biologists and land managers. Much of the attention directed toward this bird stems from a growing debate over managing old-growth forests on Federal lands, and from a concern about protecting biodiversity. We understand the significance of these larger issues, but we have kept to our mandate to develop a conservation strategy specifically for the northern spotted owl. We have concluded that the owl is imperiled over significant portions of its range because of continuing losses of habitat from logging and natural disturbances. Current management strategies are inadequate to ensure its viability. Moreover, in some portions of the owl's range, few options for managing habitat remain open, and available alternatives are steadily declining throughout the bird's range. For these reasons, delay in implementing a conservation strategy cannot be justified on the basis of inadequate knowledge. Owl Habitat and The Committee reviewed all available studies dealing with spotted owl habitat, the Population Trends relative abundance of owls related to stand age, and the relative abundance of owls in relation to various proportions of successions growth stages in the general landscape. Habitats selected by northern spotted owls typically exhibit moderate to high canopy closure; a multilayered, multispecies canopy dominated by large overstory trees; a high incidence of large trees with large cavities, broken tops, and other indications of decadence; numerous large snags; heavy accumulations of logs and other woody debris on the forest floor; and considerable open space within and beneath the canopy. These attributes are usually found in old growth, but they are sometimes found in younger forests, especially those that contain remnant large trees or patches of 1 The Conservation Strategy large trees from earlier stands. In younger forests that support breeding owls, the nest and major roost sites are usually found where large trees from the earlier, older stands remain. We evaluated the coastal redwood forests of northwestern California, where numerous owls live in stands that are mostly 50 to 80 years old. We believe their presence is attributable to the region's unique set of conditions, including a rapidly growing tree species that sprouts from stumps; intrusion of other conifer and hardwood species into the understory; relatively high rainfall; a Song growing season; and abundant prey. Under these conditions, the structural attributes that are usually associated with the presence of owls develop at an accelerated rate. We caution strongly against extrapolating these results to other parts of the owl's range. Silvicultural prescriptions might be developed that would yield significant volumes of wood products while maintaining suitable habitat for spotted owls, but we find no clear evidence that such prescriptions currently exist. Until they do, the prudent approach to ensuring the viability of the owl is to protect an adequate distribution and amount of existing habitat. Nonetheless, examining younger forests where spotted owls reproduce successfully should yield valuable insights into silvicultural techniques that could produce both wood products and owls. For at least the past century, loss of spotted owl habitat has exceeded recruitment. By some estimates (perhaps conservative), spotted owl habitat has been reduced by about 60% since 1800. The current total population of the owl is likely to be far less than once existed. The loss of habitat has not been distributed evenly across the range of the subspecies. Owl habitat is also being fragmented, a process that isolates some populations of owls. Fragmentation in the home ranges of individual birds may expose owls to greater risks of predation and competition. It may also result in habitat loss when trees blow down in high winds, and as stands suffer other impacts associated with forest edges. Determining the number of northern spotted owls in existence has drawn considerable attention. Current data do not permit a statistically reliable population estimate. The approximately 2000 pairs located during the past 5 years or reconfirmed from pre-1985 surveys represent an unknown fraction of the total population. More significantly, demographic studies from the Klamath Mountains in California and the Coast Range in Oregon indicate that populations in these study areas are declining. We propose a two-part conservation strategy. The first stage, prescribes and implements the steps needed to protect habitat in amounts and distribution that will adequately ensure the owl's long-term survival. The second stage calls for research and monitoring to test the adequacy of the strategy and to seek ways to produce and sustain suitable owl habitat in managed forests. Insights gained in this second stage can be used to alter or replace habitat conservation areas prescribed in the first stage, but only if the modified strategy can be clearly demonstrated to provide adequately for the long-term viability of the owl. 2 Our strategy largely abandons the current and, we believe, flawed system of one- to three-pair spotted owl habitat areas (SOHAs), in favor of protecting larger blocks of habitat—which we term Habitat Conservation Areas, or HCAs. Large blocks of habitat capable of supporting multiple pairs of owls, and spaced closely enough to facilitate dispersal between blocks, are far more likely to ensure a viable population than the current SOHA system. Owls in an HCA containing multiple pairs will benefit from internal dispersal of juvenile owls as well as recruitment of dispersing birds from other HCAs. Owls in HCAs containing multiple pairs are less vulnerable to random fluctuations in birth and death rates. Large HCAs reduce the impacts of habitat fragmentation and edges, and they are more resistant than SOHAs to small-scale natural disturbances. The Committee has delineated and mapped a network of HCAs necessary to ensure a viable, well-distributed population of owls. Wherever possible, each HCA contains a minimum of 20 pairs of owls. The maximum distance between these HCAs is 12 miles. Our 20-pair criterion is based on models of population persistence and empirical studies of bird populations. We have chosen 12 miles as the maximum distance between HCAs because this value is within the known dispersal distance of about two-thirds of all radio-marked juveniles studied. The HCA concept applies primarily to BLM, FS, and NPS lands, as delineated in the enclosed maps. The Committee strongly recommends that HCAs be established on State lands in certain key areas (as shown on the maps) to assure population connectivity. We also recommend that resource managers of other State lands, tribal lands, other Federal lands, and private lands use forestry and silvicultural techniques and practices that maintain or enhance habitat characteristics associated with spotted owls. In several regions, current habitat conditions and owl densities do not allow us to follow this approach. The Committee has modified the guidelines for these regions. For example, in portions of the Oregon Coast Range, habitat is currently insufficient to fully stock 20-pair HCAs with owls. We have delineated 20-pair HCAs for this area, but they will be not be capable of supporting 20 pairs of owls for many years. In the meantime, individual-pair HCAs are prescribed around all known or future pairs to reach the 20-pair target. A variety of strategies was used in other areas of special concern to help meet the intent of this strategy. Portions of the Cascade Range of northern Washington contain insufficient habitat capable of supporting 20-pair HCAs over the long term because of inherent landscape patterns. In these areas, we delineated a network of smaller HCAs but shortened the maximum distance between them to 7 miles, to facilitate dispersal. In portions of the eastern Cascade Range in Washington and Oregon, and northeast of Mount Shasta in California, relatively little owl habitat exists and spotted owls occur at low densities. We prescribe individual-pair HCAs around all known pairs and pairs located in the future. 3 Spotted owls on the Olympic Peninsula are probably demographically isolated from other populations by more than 60 miles of intensively managed State and private forest lands. We have established a large HCA on National Forest lands, but we also prescribe individual-pair HCAs around all known pairs outside the HCA and recommend smaller HCAs for State lands. Our hope is that connectivity can be restored by using a combination of HCAs and applying innovative silvicultural techniques on State and private lands. Land ownership patterns in the Coast Range of California limit our ability to establish 20-pair HCAs. We have tried to do so wherever possible, but we encourage California to work with private land owners to apply innovative silvicultural techniques to maintain or develop additional owl habitat for dispersal and breeding. We encourage Oregon and Washington to do the same. Logging (including salvage operations) and other silvicultural activities (with the exception of stand regeneration) should cease within HCAs. The Committee recognizes that allowances will have to be made for timber sales already planned and under contract in HCAs, such as sales necessary to meet Section 318 of Public Law 101-121. We considered dedicating corridors of forests between HCAs to facilitate dispersal by juvenile owls, but decided corridors were unnecessary, provided at least 50% of the forest landbase outside of HCAs is maintained in stands of timber with an average d.b.h. of 11 inches or greater and at least 40% canopy closure. We also rely on lands currently allocated to such uses as riparian corridors, streamside management zones, and special management areas for pileated woodpeckers and pine martens to provide additional habitat for dispersing spotted owls. We recommend retaining at least 80 acres of suitable owl habitat around the activity centers of all known pairs of owls in the managed forest, up to a total of seven per township. These centers will serve as older forest nuclei that could become core areas for future breeding pairs of spotted owls as the surrounding forest matures. If healthy populations of northern spotted owls can be sustained in the managed forest, HCAs will no longer be necessary. Timber harvests that affect owl pairs outside the conservation areas are therefore viewed as experiments in managing for spotted owl habitat. Consequences for The Committee believes this conservation strategy, if faithfully implemented, has a the Northern high probability of retaining a viable, well-distributed population of northern spotted Spotted Owl owls over the next 100 years. The HCAs on Federal lands contain 925 known pairs of owls, and we estimate the actual number to be about 1465 pairs. Regeneration of younger stands within HCAs on Federal lands should enable the spotted owl population to increase to about 1759 pairs. These numbers are important, but only up to a point; the amount and spacing of habitat are as critical to the viability of the subspecies as the actual numbers. 4 Implementing the Conservation Strategy Assessment of Impacts Under a worst-case scenario, even with this conservation strategy fully implemented, a short-term loss of a significant portion of the existing population of northern spotted owls is likely. We do not take this loss lightly, but we believe the subspecies can withstand a reduction provided our strategy is followed. Even under the most stringent scenarios of habitat protection, a similar reduction in the number of existing pairs over time seems likely because many pairs of owls live in highly fragmented and marginal habitats isolated from other pairs. Implementing a comprehensive strategy for the spotted owl requires a well-coordinated program of research, monitoring, and habitat management by State and Federal agencies and private landowners. Much room for improvement exists. So far as we can determine, for example, no plans have been made within or among agencies to determine what changes in population size or habitat conditions would trigger a review of, and possible changes in management actions needed to ensure the welfare of the owl. We urge that a coordinator and interagency staff (State and Federal) be assigned to oversee the conduct of the conservation strategy. The coordinating group would have the additional duty of recommending alterations to our conservation strategy. The plan put together by our Committee, however, is a strategy for the entire U.S. range of the northern spotted owl. No part of the strategy was designed to stand alone, and proposed changes must be considered in that light. Our assignment was to develop a scientifically credible conservation strategy for the northern spotted owl. We recognize that the impacts of the strategy we propose will be analyzed by others. The immediate response, we expect, will be to focus almost solely on the short-term economic and social impacts of implementing the strategy as it affects the availability of timber. This assessment is critically important. Adoption of the conservation strategy, however, has significant ramifications for other natural resources, including water quality, fisheries, soils, stream flows, wildlife, biodiversity, and outdoor recreation. All of these aspects must be considered when evaluating the conservation strategy. The issue is more complex than spotted owls and timber supply—it always has been.