A Disturbance-Based Ecosystem Approach to Maintaining and Restoring Freshwater Habitats of Evolutionarily Significant Units of Anadromous Salmonids in the Pacific Northwest

-To preserve and recover evolutionarily significant units (ESUs) of anadromous salmonids Oncorhynchus spp. in the Pacific Northwest, long-term and short-term ecological processes that create and maintain freshwater habitats must be restored and protected. Aquatic ecosystems throughout the region are dynamic in space and time, and lack of consideration of their dynamic aspects has limited the effectiveness of habitat restoration programs. Riverine-riparian ecosystems used by anadromous salmonids were naturally subjected to periodic catastrophic disturbances, after which they moved through a series of recovery states over periods of decades to centuries. Consequently the landscape was a mosaic of varying habitat conditions, some that were suitable for anadromous salmonids and some that were not. Life history adaptations of salmon, such as straying of adults, movement of juveniles, and high fecundity rates, allowed populations of anadromous salmonids to persist in this dynamic environment. Perspectives gained from natural cycles of disturbance and recovery of the aquatic environment must be incorporated into recovery plans for freshwater habitats. In general, we do not advocate returning to the natural disturbance regime, which may include large-scale catastrophic processes such as stand-replacing wildfires. This may be an impossibility given patterns of human development in the region. We believe that it is more prudent to modify humanimposed disturbance regimes to create and maintain the necessary range of habitat conditions in space (103km) and time (101-102 years) within and among watersheds across the distributional range of an ESU. An additional component of any recovery plan, which is imperative in the short-term, is the establishment of watershed reserves that contain the best existing habitats and include the most ecologically intact watersheds. . Biodiversity is not a ‘set-aside’ issue that can be physicallyisolated in a few, or even many, reserves.... We on all of the landscape with every activity we undertake as human beings-a task without spatial and temporal boundaries. (J. F. Franklin 1993) and degradation, overexploitation in sport and commercial fisheries, variable ocean conditions, and efdepressed status of these fish (Nehlsen et al. 1991). The relative importance of each in contributing to the decline of an ESU undoubtedly varies across the must see the larger task-stewardship of all the species fects of hatchery practices, are responsible for the Agencies responsible for the development of recovery plans for evolutionarily significant units (ESUs; Waples 1991) of anadromous salmonids Oncorhynchus spp. in the Pacific Northwest (PNW) of the United States face difficult tasks. First is the identification of ESUs. Second is the identification of factors that contribute to the decline of a particular ESU. A suite of factors, including habitat loss 334 region. Any recovery program must address and incorporate consideration of all responsible factors to be successful. The most common factor associated with declines of anadromous salmonids is habitat degradation, which includes destruction and modification of freshwater and estuarine habitats (Nehlsen et al. 1991; Frissell 1993). Stream and river systems DISTURBANCE-BASED HABITAT RECOVERY PLAN 335 throughout the PNW have been extensively altered by human activities such as agriculture, urbanization, and timber harvest (Bisson et al. 1992). Features of altered ecosystems include changes (generally reductions) in species diversity, changes in species distributions, and losses of habitat types or ecosystem states (Holling 1973; Rapport et al. 1985; Steedman and Regier 1987). Li et al. (1987), Bisson et al. (1992), and Reeves et al. (1993) noted that native salmonid assemblages are simplified in watersheds that have been impacted by various human activities. Native nonsalmonids or introduced species often dominate fish communities in altered ecosystems (Li et al. 1987; Bisson et al. 1992). Habitat degradation is widespread across the region as a result of past and present activities (Bisson et al. 1992; McIntosh et al. 1994). Degradation of terrestrial ecosystems in the PNW (Thomas et al. 1993) and elsewhere (e.g., Wilcove et al. 1986; Rolstad 1991) has resulted in similar changes in terrestrial species assemblages. Past and many present approaches to management of freshwater habitats of anadromous salmonids have focused on mitigating losses rather than preventing them. This strategy has generally not been successful (Bisson et al. 1992) and habitat loss and degradation continue. Williams et al. (1989) also found that such a strategy failed to halt the decline of habitat quantity and quality for other freshwater fishes. Naturally variable ocean conditions increase the importance of freshwater habitats to anadromous salmonids (Thomas et al. 1993). As a result of this dependence on freshwater habitats and the extensive amount of habitat degradation that has occurred, protection and restoration of upslope and fluvial processes that create and maintain habitats must be an integral component of any recovery program. Habitat losses may result from human activities that directly destroy habitats or change the longterm dynamics of ecosystems (Rapport et al. 1985; Webb and Thomas 1994). Recent proposals for restoring and protecting habitats of at-risk fishes (e.g., Reeves and Sedell 1992; Thomas et al. 1993; Moyle and Yoshiyama 1994) addressed habitat destruction, primarily through the establishment of watershed-level reserves in which human impacts would be minimized, as advocated by Sheldon (1988) and Williams et al. (1989). We are not aware of anyone who has explicitly addressed long-term ecosystem dynamics in the context of fish conservation. Williams et al. (1989) called for recovery efforts to restore and conserve ecosystems rather than simply habitat attributes, but they did not state how to accomplish this. Williams et al. (1989) also noted that the failure to address this concern may be a major reason no fish species has ever been recovered after listing under the U.S. Endangered Species Act (ESA, 16 U.S.C. §§1531 to 1544). The purpose of this paper is to examine components of strategies necessary to provide habitat for ESUs of anadromous salmonids in the PNW. Specifically, we will consider the role of natural disturbances in creating and maintaining habitats and how an understanding of this role might be incorporated into long-term recovery planning. Ecosystem and Spatiotemporal