Synthesis of Ecosystem Resources and Threats 135 ECOSYSTEM RESTORATION ON SANTA CATALINA ISLAND: A SYNTHESIS OF RESOURCES AND THREATS Denise A. Knapp University of California, Santa Barbara Ecology, Evolution, and Marine Biology Department Santa Barbara, CA 93106-9610 [email protected] ABSTRACT: Catalina Island‘s oaks provide habitat for a diverse array of plants and animals, many of them rare. The oak ecosystem encompasses a large majority of the island, yet the foundation of this system, the oaks themselves, appear to be in decline. Seaver Institute funds allowed the Catalina Island Conservancy and its partners to initiate a variety of ecological research projects and restoration initiatives using an ecosystem-level approach. In this paper, the natural resources of the island are discussed (with an emphasis on those depending on oaks), along with the threats to those resources and natural processes. Oak habitat dominated by Quercus pacifica has declined by as much as 31 percent over the past 60+ years on the island, with no apparent recruitment into the canopy. Low moisture, poor dispersal, trampling by bison, and browsing by mule deer appear to be limiting regeneration of this species, the adults of which are likely dying due senescence (old age) hastened by stressors such as browsing by introduced ungulates. Quercus tomentella is restricted to seven locations on the island, yet maintains relatively high genetic diversity; the greatest threats to this species are likely small population sizes, fragmentation, deer browsing, and root exposure caused by erosion. A multitude of invasive, transformer species threaten the island‘s native and endemic species, along with hydrologic alteration, roads, and increased fire frequency. Climate change is expected to exacerbate these existing threats, which themselves interact, thus compounding and complicating their impacts. Although important steps have already been taken towards protecting Catalina‘s ecosystem, such as feral goat and pig removal and transformer plant control, much more action will be necessary if structure and function are to be improved. Future restoration priorities should take into account the degree of the threat, the chances of success, and the benefits to be derived from such action. The groundwork for setting those priorities has been laid here; management recommendations will be presented elsewhere. The ecosystem framework and collaborative approach taken here has had a multitude of benefits, including efficient use of funds and the creation of partnerships; the result has been the true integration of science and management. KEYWORDS: Catalina Island, dieback, ecosystem, oak regeneration, Quercus pacifica, Quercus tomentella, restoration, transformer species TABLE OF CONTENTS INTRODUCTION………………………………………………………………………………………136 Background……………………………………………...………………………………………………136 Defining the oak ecosystem on Catalina…………………………………………………...……… .137 Setting and island history…………………………………………………………………….…….…..137 BIOLOGICAL RESOURCES……………………….……………………………………….……… ..143 Oak species……………………………………………………………………………………………… 143 Associated flora………………………………………………………………………………………… 144 Associated fauna…………………………………………………………………………………….….. 147 THREATS TO THE ISLAND’S OAKS…………………………………………………………..…. 150 Quercus pacifica……………………………………………………………………………………..…. 150 Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA. Synthesis of Ecosystem Resources and Threats 136 Quercus tomentella……………………………………………………………………………………. ..153 THREATS TO THE ISLAND ECOSYSTEM…………………………………………………….…..153 Non-native, transformer species…………………………………………………………………..…... 154 Ungulates…………………………………………………………………………………………...…… 155 Feral goats………………………………………………………………………………………………..157 Feral pigs……………………………………………………………………………………………...….157 American bison……………………………………………………………………………………..…… 159 Mule deer…………………………………………………………………………………………….….. 160 Carnivores and rodents………………………………………………………………………………….. 163 Feral cats…………………………………………………………………………………………………163 Rats………………………………………………………………………………………………………. 165 House mouse…………………………………………………………………………………………..… 168 Birds………………………………………………………………………………………………...…… 169 European starling…………………………………………………………………………………..…….169 Wild turkey…………………………………………………………………………………………..….. 171 Brown-headed cowbird………………………………………………………………………………….. 172 Amphibians…………………………………………………………………………………………….…172 American bullfrog…………………………………………………………………………………..…… 172 Invertebrates…………………………………………………………………………………………….. 174 European honeybee……………………………………………………………………………………… 174 Argentine ant………………………………………………………………………………………….… 175 Transformer Plants………………………………………………………………….……………...…... .177 Roads……………………………………………………………………………………………………..180 Hydrologic alteration…………………………………………………………………………………... 183 Fire………………………………………………………………………………………………………. 185 Fire history………………………………………………………………………………………………. 185 CONCLUSIONS………………………………………………………………………………………. 187 ACKNOWLEDGMENTS……………………………………………………………………………... 188 LITERATURE CITED…………………………………………………………………………………189 INTRODUCTION Background Oak trees provide food, shelter, and habitat for a diverse array of native plants and animals in California (Block et al. 1990; Pavlik et al. 1991), including over half of the state‘s native terrestrial vertebrates (Tietje and Vreeland 1997). Oak woodland is more species rich than any other vegetation type in the state (Barrett 1980; Verner 1980; Garrison 1996), and oak trees play an important role in maintaining water quality, stabilizing slopes, and increasing soil fertility (Jackson et al. 1990; Dahlgren et al. 1997; McCreary 2004). Yet over half of California‘s oak woodland has been lost due to clearing for rangeland, agriculture and viticulture, and fuelwood, and conversion to residences and industry (Burcham 1957; McCreary 2004). Simultaneously, existing stands of several oak species in California are in decline due to a wide variety of postulated factors including introduced species, altered disturbance regimes such as fire and flood, acorn and seedling predation, and fragmentation (Griffin 1971; McClaran 1986; Borchert et al. 1989; Brown and Davis 1991; Davis et al. 1991; Meyer 2002; Tyler et al. 2006; Zavaleta et al. 2007). Many of the species showing stand level decline also show poor regeneration at the individual and stand levels, and little is known about what limits both their regeneration and their stand level dynamics. Oak ecosystem restoration on Santa Catalina Island, California: Proceedings of an on-island workshop, February 2-4, 2007. Edited by D.A. Knapp. 2010. Catalina Island Conservancy, Avalon, CA. Synthesis of Ecosystem Resources and Threats 137 On Santa Catalina Island (hereafter Catalina), oak woodlands are important both ecologically and culturally. The two predominant oaks are Island scrub oak (Quercus pacifica) and Island oak (Quercus tomentella). Together, they cover over 23% of Catalina (Figure 1), and comprise ecosystems that encompass a large number of associated plant and animal species. It is thus alarming that oaks on Catalina appear to be declining, with the island‘s most prominent oak species, Quercus pacifica, exhibiting stand- level dieback (Knapp 2002), primarily on the Channel side of the island (Figure 2), and little recruitment noted for either species over the past several decades. The Catalina Island Conservancy (hereafter Conservancy) owns and manages 88% of Catalina. In 2003, the Conservancy received a grant from the Seaver Institute to begin restoration of the island‘s oak ecosystem. A variety of ecological research projects were then initiated on the Island between 2003 and 2007 in order to learn more about the condition and dynamics of the oak ecosystem and to inform restoration and management. At the same time, a variety of projects have catalyzed oak ecosystem restoration on the island. The purposes of this paper are to describe the natural resources of Catalina with specific reference to oaks and to discuss the factors that threaten those resources and the natural processes on the island. The accomplishments of the recent oak ecosystem-related research and restoration activities will also be discussed. Recommendations for ecosystem-level restoration have been provided to the Conservancy but are not presented here, at the Conservancy‘s request. Defining the Oak Ecosystem on Catalina The Society for Ecological Restoration (SER International 2004) defines an ecosystem as consisting of ―the biota (plants, animals, microorganisms) within a given area, the environment that sustains it, and their interactions.‖ Thus, the ecosystem approach is holistic rather than species-specific, and focuses on the maintenance of ecological processes and community mosaics at multiple scales (Ehrenfeld 2000). The ecosystem, from such a holistic viewpoint, includes ecological processes such as the movement of individuals as well as the maintenance of sustainable populations across landscapes. Catalina‘s oak trees occupy a broad spectrum of plant community types, including woodland, riparian, chaparral, coastal scrub, and grassland. They can comprise the dominant species in some woodland types, or they can be part of a more diverse riparian or chaparral assemblage. They can be found from the tops of ridges to the edges of streams, and from the shoreline to the most interior slopes (Figure 3). The wildlife that are found within their influence also commonly depend on adjacent