Jeanne C. Chambers is research ecologist with the USDA Forest Service, Rocky Mountain Research Station in Reno, Nevada; she served as the team leader of the Great Basin Ecosystem Management Project.

Jerry R. Miller is the Blanton J. Whitmire Distinguished Professor of Environmental Sciences at Western Carolina University in Sylva, North Carolina.

Restoring and Maintaining Sustainable Riparian Ecosystems: The Great Basin Ecosystem Management Project

JEANNE C. CHAMBERS AND JERRY R. MILLER

In the Great Basin, as in other semiarid regions, riparian areas exhibit widespread degradation. It has been estimated that more than 50 percent of the riparian areas (streams and their associated riparian ecosystems) in the Great Basin are currently in poor ecological condition (Jenson and Platts 1990). The ongoing deterioration of these areas is of significant concern to land managers and other stakeholders who value these watersheds for a variety of purposes. Riparian areas are important components of all landscapes, but in the semiarid Great Basin they constitute an especially vital resource. Although they comprise less than 1 percent of the Great Basin, they supply many critical ecosystem services. Riparian areas supply water for both culinary and agricultural uses, forage and browse for native herbivores and livestock, and recreational opportunities. In addition, they serve as the foundation for much of the region's biodiversity. Riparian areas in the Great Basin provide habitat for a wide array of organisms such as butterflies (Fleishman et al. 1999) and Neotropical migrant birds (Martin and Finch 1996), and support a relatively high number of endemic species, including the Lahontan cutthroat trout (Oncorhynchus clarki henshawi), which is listed as threatened under the U.S. Endangered Species Act (Dunham et al. 1997).

Degradation of riparian areas in the Great Basin is the result of complex and interrelated responses of geomorphic, hydrologic, and biotic processes to climate change and natural and anthropogenic disturbances. These disturbances can alter the hydrologic or sedimentologic regime of a fluvial (river or stream) system and produce changes in the physical foundations of riparian ecosystems, such as stream channel characteristics and surface-groundwater interactions. Ultimately, they alter the structure and functioning of riparian ecosystems. In this volume, anthropogenic disturbances refer to all human activities that affect physical and biological processes within a watershed, while natural disturbances include phenomena such as floods, landslides, and wildfires. Although climate change could be considered to be a type of natural disturbance, it operates over longer temporal scales and larger spatial scales than most other forms of natural disturbance. Also, current shifts in climate arguably are related to human activities. Thus, climate change is treated as a special form of disturbance herein.

Much of the research on stream and riparian ecosystem degradation in arid and semiarid regions of the western United States has focused on the effects of anthropogenic disturbances. Consequently, the degradation of these riparian areas has been attributed largely to human activities, and management and restoration strategies have focused primarily on anthropogenic disturbances. In the Great Basin, riparian areas and their associated uplands have been subjected to various anthropogenic disturbances since European settlement of the region around 1860. The most extensive disturbances have been overgrazing by livestock (Kauffman and Krueger 1984; Fleischner 1994; Ohmart 1996; Trimble and Mendel 1995; Belsky et al. 1999) and road construction in the valley and canyon bottoms. Local alterations of hydrologic regimes via dams and water diversions, mining operations, and recreational activities also have had negative influences on riparian ecosystems (Sidle and Amacher 1990; Sidle and Hornbeck 1991). The influences of these disturbances on riparian areas have been well documented and management strategies for mitigating their effects are discussed in numerous locations (e.g., Kusler and Kentula 1990; National Research Council 1992, 2002; Briggs 1996; Kauffman et al. 1997; Williams et al. 1997).

The effects of past and present climate change on stream and riparian ecosystems have received considerably less attention than the influences of anthropogenic disturbance. This is surprising given that arid and semiarid regions like the Great Basin are more sensitive to the effects of both past and present climate change than humid regions. The sensitivity of these regions to climate change has important implications for the types and characteristics of disturbances that riparian areas experience, and the effects of these disturbances on riparian ecosystems. In comparison to humid regions, arid and semiarid regions generally exhibit amplified runoff responses to precipitation change (Dahm and Molles 1991), have higher streamflow variability (Poff 1991; Osterkamp and Friedman 2000), and have more severe flash floods (Graf 1988; Osterkamp and Friedman 2000). In the Great Basin, paleoecological and geomorphic records indicate that there have been significant fluctuations in climate during the Holocene (approximately the past ten thousand years) (Tausch and Nowak 2000), and that these fluctuations have had major effects on disturbance regimes (Miller et al. 2001). Changes in hillslope processes, stream channel pattern and form, surface and groundwater interactions, and riparian vegetation composition and structure over time scales of hundreds of years have all been attributed to Holocene shifts in climate (Chambers et al. 1998; Miller et al. 2001). Perhaps more important from a management and restoration perspective is that the effects of these changes on hillslope processes and landforms have persisted for hundreds to thousands of years. For example, a shift from moister to drier conditions during the mid- to late-Holocene led to accelerated hillslope erosion, sediment deposition on alluvial fans and in valley bottoms, and a depletion of hillslope sediment supplies in upland watersheds of the central Great Basin (Miller et al. 2001). These climate-induced changes still influence geomorphic processes and, thus, channel pattern and form.

The failure of past restoration activities in semiarid riparian areas to meet desired goals has been attributed to a general lack of understanding of existing physical and biotic processes and the causes of disturbance (Elmore and Kauffman 1994; Kauffman et al. 1997;...