Monographs of the Western North American Naturalist

Volume 7 8th California Islands Symposium Article 28

12-31-2014 Ecosystem restoration on Santa Catalina Island: a review of potential approaches and the promise of bottom-up invader management Denise A. Knapp Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, CA, [email protected]

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Recommended Citation Knapp, Denise A. (2014) "Ecosystem restoration on Santa Catalina Island: a review of potential approaches and the promise of bottom-up invader management," Monographs of the Western North American Naturalist: Vol. 7 , Article 28. Available at: https://scholarsarchive.byu.edu/mwnan/vol7/iss1/28

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ECOSYSTEM RESTORATION ON SANTA CATALINA ISLAND: A REVIEW OF POTENTIAL APPROACHES AND THE PROMISE OF BOTTOM-UP INVADER MANAGEMENT

Denise A. Knapp1

ABSTRACT.—Restoring large, complex landscapes can be challenging, especially given that some threats to native diversity and ecological function cannot be wholly eliminated. Santa Catalina Island, California, provides a valuable case study because its challenges include a variety of ecosystem threats, legal restrictions, and cultural attachments, as well as a vocal resident human population that often does not agree with conservation actions. Catalina Island has been highly modified by numerous invasive species, fragmentation and erosion from roads, altered hydrology from dams, and increased fire frequency. In this paper, I build on a previously published review of resources and threats and discuss potential management actions for those threats. Although the island’s large size, rugged topography, and pervasive human influence limit management options, several feasible actions could have an important restorative effect. In par- ticular, “bottom-up” invader management may be a relatively noncontroversial way to produce multiple positive out- comes. Reducing fragmentation, restoring natural hydrologic regimes, and augmenting native plant cover could disad- vantage invasive plant and animal species while promoting the native flora and fauna.

RESUMEN.—El desafío de restaurar grandes y complejos paisajes puede ser difícil, especialmente porque algunas amenazas a la diversidad nativa y funciones ecológicas no pueden ser eliminadas por completo. La Isla Santa Catalina, California, proporciona un valioso caso de estudio, ya que cuenta con una variedad de amenazas al ecosistema, restric- ciones legales y añadidos culturales, así como una población humana residente que a menudo no está de acuerdo con las medidas de conservación. La Isla Catalina ha sido modificada por numerosas especies invasoras, la fragmentación y la erosión por los caminos, la hidrología alterada por las presas y un aumento en la frecuencia de incendios. En este artículo, construyo sobre un resumen previamente publicado de recursos y amenazas, y discuto las acciones potenciales de intervención para tales amenazas. Aunque el gran tamaño de la isla, la topografía escabrosa y la influencia humana limitan algunas opciones de intervención, varias acciones factibles podrían tener un efecto fortalecedor importante. En particular, el tratamiento “bottom up” (de abajo hacia arriba) del invasor podría ser una forma relativamente no contro- versial de producir múltiples resultados positivos. La reducción de la fragmentación, la restauración de los regímenes hidrológicos naturales y el aumento de la cobertura vegetal nativa podrían crear una desventaja para las especies de ani- males y de plantas invasoras, y promover la flora y fauna nativa.

Challenges of large-scale ecological resto - human influence reduce the likelihood that ration include technical issues such as ubiqui- many transformer species can be eradicated. tous and tenacious invasive species, institu- Thus, the island’s land managers need to tional constraints such as funding and legal develop cost-effective, alternative means of restrictions, and social challenges such as pub- reducing the adverse impacts of such species. lic resistance. Given these challenges, some A focus on species interactions, community threats to native species and ecoystems cannot dynamics, and ecosystem processes can be be wholly eliminated. Santa Catalina Island, especially important for identifying those California, provides a case study of such land management alternatives (Zavaleta et al. 2001, management challenges. The island has expe- Rayner et al. 2007). rienced a variety of anthropogenic stressors, Here, I discuss restoration alternatives for including invasion by numerous transforma- the major threats to Catalina Island’s resources tive nonnative species, fragmentation and ero- that were reviewed in Knapp (2010a), and I sion from roads, altered hydrology from dams, highlight how land managers might benefit and increasing fire frequency, which have left from undertaking “bottom-up invader man- the ecosystem highly modified. The island’s agement” actions. Bottom-up invader manage- large size, rugged topography, and pervasive ment (sensu McEvoy and Coombs 1999)

1Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, CA 93105. E-mail: [email protected]

421 422 MONOGRAPHS OF THE WESTERN NORTH AMERICAN NATURALIST [Volume 7 emphasizes the use of resource limitation to city (Avalon), and the island receives about one control invaders instead of top-down control million visitors per year (Catalina Island methods, such as hunting. It may involve miti- Chamber of Commerce and Visitors Bureau gation of stressors on native taxa, manipulation 2012), the majority of whom remain in Avalon. of disturbance regimes, soil conditions, and The founding of Avalon led to increased other abiotic factors, or increasing competi- development of the rest of the island, includ- tion through actions such as seeding native ing a stagecoach route and hunting lodge; a plants (D’Antonio and Chambers 2006). Such World War II camp; ranch settlements, dams, activities on Catalina Island may also include and camps in the majority of the island’s dam and road removal, which are relatively coves; and an airport carved off of one of the noncontroversial actions that would not only tallest peaks on the island. Today, the Catalina ease the immediate stressors of hydrologic Island Conservancy (hereafter, Conservancy) alteration, fragmentation, and denudation but owns and manages 88% of the island; its mis- would also have the secondary benefit of sion is to be a responsible steward of the land putting many of the island’s plant and animal through a balance of conservation, education, invaders at a disadvantage. and recreation. The Conservancy has taken important steps Setting and Management History to recover the island from centuries of human At 194 km2, Catalina Island is the third impacts. Feral goats and pigs have been re- largest of the 8 California Channel Islands moved, a hunting program is maintained for and is located approximately 32 km from the mule deer, and bison are managed through a southern California mainland coast (Schoen- contraception program. The most transforma- herr et al. 1999). The island is characterized tive nonnative plant species have been identi- by numerous steep canyons; perennial streams fied, and they are being managed throughout are limited to a few dominant canyons near the island by focusing simultaneously on the center of the island. The island has a long eradication of limited-abundance, high-impact history of human use, from native Tongva species and control of more widespread species settlements to Spanish missionaries, Yankee in priority areas (Knapp 2010b, Knapp et al. traders, and otter hunters in the early 1800s, 2011). The Catalina Island fox (Urocyon lit- and squatters, miners, and Union soldiers in the toralis catalinae) has been brought back from mid-1800s (Moore 2009). Between the mid- the brink of extinction, following an outbreak 1800s and mid-1900s, multiple ungulates were of canine distemper virus, through a combina- introduced, including feral goats (Capra hircus), tion of translocations, captive breeding, and feral pigs (Sus scrofa), American bison (Bison vaccinations (Coonan et al. 2010). Yet much bison), mule deer (Odocoileus hemionus cali- more remains to be done to ensure the persis- fornicus), domestic sheep (Ovis aries), and cattle tence of at least 42 taxa found only on Cata- (Bos taurus), resulting in the deterioration of lina Island (as well as a number of other habitat (Coblentz 1980). Sheep and cattle were Channel Island endemic taxa) and to maintain the first nonnative animals to be eliminated diverse, resilient communities. Herein I review on the island by the mid-1920s and late 1950s, management alternatives for threats stemming respectively (O’Malley 1994). Cumulatively, from invasive species and habitat alteration browsers have reduced the extent of shrub- and discuss how managing the latter may be a land on the island, which has been replaced means to help manage the former. with introduced annual grasses (Minnich 1982). Introduced ungulates have also caused the open THREAT MANAGEMENT OPTIONS understory of much of the island’s oak stands. AND FEASIBILITY The consequent reduction of vegetation struc- ture and diversity has undoubtedly reduced Mule Deer the abundance and diversity of the wildlife The impacts of introduced deer species are that depend on it, from invertebrates (Lawton especially severe on islands, where deer lower 1983, Bennett 1993) to native vertebrates species richness, change community composi- (Tietje and Vreeland 1997, Sillett et al. 2012). tion, endanger rare plants, and reduce wildlife Catalina Island is the only one of the 8 Cali- populations of various trophic levels (reviewed fornia Channel Islands with an incorporated in Knapp 2010a). On Catalina Island, mule 2014] ECOSYSTEM RESTORATION ON CATALINA ISLAND 423 deer reduce shrub and tree cover and sur- Island landscape and a source of ecotourism vivorship, particularly postfire (reviewed in dollars. Restriction of their range to a location Knapp 2010a). In contrast to many of the other most visible to tourists could be a viable solu- invasive wildlife species on the island, mule tion and is the option favored by research scien - deer eradication on Catalina Island is tech - tists (Sweitzer et al. 2003). Restricting bison nically feasible, as evidenced by the prior presence to the most heavily toured area of removal of both feral goats and feral pigs the island would balance maintenance of the (Schuyler et al. 2002a, 2002b), the recent re - ecological integrity of the island with cultural moval of deer and elk (Cervus elaphus) on and economic considerations. nearby Santa Rosa Island (Kettmann 2011), and Cats and Rats improvements in the technology available to detect and dispatch ungulates, thus ensuring Cats (Felis catus) and rats (Rattus spp.) are their complete removal (Morrison et al. 2007). believed to be responsible for the extinction An increase in native perennial grasses and of hundreds of taxa, including birds, small shrubs, as well as a decrease in exotic annual mammals, herpetofauna, and invertebrates (re - grasses, was found on Santa Rosa Island fol- viewed in Knapp 2010a). In addition, rats can lowing removal of cattle and reduction of both restrict plant regeneration and abundance, Roosevelt elk and mule deer herds, although and cats are believed to compete with the effects vary by taxa, functional group, and Catalina Island fox (reviewed in Knapp 2010a). physical environment (Christian et al. 2008, The ecological effects of these 2 species on Corry and McEachern 2008, Dow et al. 2008). Catalina Island are not well understood, how- Mule deer eradication would require either ever, and it is possible that the presence of a permission from the California Department native predator, the fox, moderates feral cat of Fish and Game, which has legal jurisdiction impacts (McChesney and Tershy 1998). over the deer, or a change in state law. The Management of introduced cats and rats on Conservancy has sought permission for private Catalina Island is complicated by their com- control over management efforts with little bined presence, as well as the presence of success to date. A change in state regulation multiple nontarget species, such as native would likely be required. Mule deer have been rodents, birds, and foxes. Removal of cats harvested almost annually on the island from without control of introduced rats could have 1949 through the present, most recently as the unintended consequence of reducing na - part of the Private Lands Management Pro- tive wildlife populations even further through gram of the California Department of Fish and mesopredator release (Courchamp et al. 1999, Game. However, recreational hunting alone Rayner et al. 2007). Fan et al. (2005) recom- is unlikely to sufficiently control an invasive mend controlling the rodents first and the mammal such as mule deer (Mack et al. 2000). cats second, or controlling both simultaneously. Although eradication of rodents first may fur- American Bison ther increase predation by cats on threatened American bison reduce plant diversity and native species (Courchamp et al. 1999), the cover on Catalina Island, simplify habitat benefits of eventual removal of the super- structure, trample woody species such as oak predator may outweigh the immediate costs trees, and facilitate the dispersal of nonnative of mesopredator release (Russell et al. 2009). plants. However, they also appear to have the Transformer rodents such as rats have been beneficial effect of controlling invasive annual eradicated from 284 islands, the largest of grass densities (reviewed in Knapp 2010a). which is 11,300 hectares (Howald et al. 2007). Bison are currently managed to approximately Aerially applied rodenticide is used in the 150–200 individuals on roughly one-half of the majority of those eradications (Howald et al. island via immunocontraception (Duncan et 2007), and captive management or transloca- al. 2013). Their complete removal would be tion of native species in danger of nontarget technically feasible, given prior success of poisoning can reduce impacts to those species roundup efforts on the island and removal (e.g., Shah 2001, Merton et al. 2002, Howald of ungulates on multiple other islands. There et al. 2005). Feral cats have been removed would be social obstacles, however, as the from at least 48 islands globally, the largest of bison are a beloved feature of the Catalina which is Marion Island, at 290 km2, or 71,660 424 MONOGRAPHS OF THE WESTERN NORTH AMERICAN NATURALIST [Volume 7 acres (reviewed in Nogales et al. 2004). How- nonnative plant species over natives (reviewed ever, that removal was accomplished only in Knapp 2010a). Due to the starling’s status with 19 years of sustained effort and multi- as an agricultural pest, much effort and fund- ple methods on an island with no permanent ing has been expended on its deterrence and human population (Bester et al. 2002). This control (e.g., Garner 1978). Harassment using long-term commitment and lack of public both visual and sonic frightening devices has op position was undoubtedly critical to that been utilized in the United States, but with project’s success. Cats were recently removed little success (Brough 1969, Clark 1976, Garner on San Nicolas Island, California, primarily 1978, Belant et al. 1998, Seamans et al. 2001, through live capture (Hanson et al. 2010, Blackwell et al. 2002). Such deterrents are not Stephenson-Pino 2012). However, the modified successful in the long term and only move the padded leghold traps used on that project are problem elsewhere (Feare et al. 1981, Dinetti only legal on federally owned lands in Cali- 2006). Several methods of lethal control have fornia (Hanson et al. 2010). been used, including application of a chemical The eradication of both cats and rats on the avian stressing agent (Starlicide), dynamiting, entire Catalina Island would be hindered by and shooting (Clark 1976, Garner 1978, Feare the presence of vocal opponents, the exis- 1991). The avian stressing agent reduced the tence of extensive cat colonies on public land, starling population to varying degrees, from the large size and ruggedness of the island, <1% to 99% (Garner 1978). Killing programs and the presence of nontarget native species. for bird pests are expensive and generally Localized control in priority areas could be a unsuccessful, due to both immigration from viable management alternative to eradication neighboring areas and compensatory repro- (Jouventin et al. 2003, Ogden and Gilbert duction (Feare 1991). Furthermore, some of 2009); however, long-term efforts can be pro- the methods are particularly inhumane. hibitively costly (Howald et al. 2005) and The most promising avenue for starling toxin buildup in the environment or evolu- control is through habitat management. Gen- tion of toxin resistance is a concern (Innes and erally, starlings favor disturbed, homogeneous Barker 1999). Rat-proof exclosures, such as habitat (such as agricultural fields or invaded those described by Campbell and Atkinson monocultures); therefore, their concentrations (2002) or Day and MacGibbon (2007), have could be limited by enhancing native habitat been used successfully and can minimize the cover and heterogeneity (Clergeau and Fourcy need for ongoing control. They are being used 2005). One component of this approach may to protect areas up to 250 ha in New Zealand be herbivore removal. Diamond and Veitch (McLennon 2006) and could conceivably be (1981) have reported that browsers and grazers altered to exclude cats as well. are a factor in bird invasion, along with habi- Habitat restoration could limit the impacts tat fragmentation. of invasive rats. In Madagascar, rats were Wild Turkeys more abundant in smaller habitat fragments, while endemic rodents declined in such frag- It is not known if Wild Turkeys (Meleagris ments (Ganzhorn 2003). Unnecessary roads gallopavo) still occur on Catalina Island. How- could be removed and revegetated in order to ever, if they do still exist, they are expected to provide the contiguous habitat that favors have negative effects on plant regeneration, native species over these invaders. Addition- particularly oaks (reviewed in Knapp 2010a). ally, immunocontraception, including that vec- Under the precautionary principle, land man- tored by species-specific viruses, may be a agers have eradicated Wild Turkeys from Santa promising technique (Courchamp et al. 2003, Cruz Island (Morrison 2007). Wild turkey re- Hardy et al. 2006). moval on Catalina would be relatively feasible, given their limited distribution and large size. European Starlings Brown-headed Cowbirds European Starlings (Sturnus vulgaris) have negative effects on other members of the Brown-headed Cowbirds (Molothrus ater) woodpecker family, as well as on some birds in are brood parasites and may have a substantial other families (reviewed in Knapp 2010a). adverse effect on rare passerine bird popula- They also preferentially disperse seed of tions (reviewed in Knapp 2010a). Like the 2014] ECOSYSTEM RESTORATION ON CATALINA ISLAND 425

European Starling, the Brown-headed Cowbird The best prospects for invasive bullfrog is favored by human-modified habitats and control appear to be habitat management fragments (Lowther 1993). Trapping at impor- (Adams and Pearl 2007). Because bullfrogs tant breeding areas has been the only means overwinter as larvae (tadpoles) in the water, of successful control of Brown-headed Cow- they generally cannot live in water sources birds to date (Lowther 1993). Research con- that frequently dry up (Orchard 1999, Maret ducted by Staab and Morrison (1999) suggests et al. 2006). The Conservancy could actively that riparian management favoring greater manage ponds and reservoirs on the island understory cover can help to reduce para- to favor native wildlife by promoting more sitism by this species. This objective could ephemeral wetland habitats over permanent be promoted by ungulate removal and habitat ponds (Adams 1999, 2000, Maret et al. 2006) restoration, as with starlings. and by encouraging shallow water, sloping banks, and emergent vegetation (Kiesecker et American Bullfrogs al. 2001, Porej and Hetherington 2005, Adams American bullfrogs (Rana catesbeiana) are and Pearl 2007, Minowa et al. 2008). Dam believed to be at least partly responsible for removal would facilitate these goals. the decline or extinction of 7 native frogs in the European Honey Bees Southwest, along with many other native amphibians elsewhere in the world. They pose The balance of evidence suggests that a risk to snake and fish populations (reviewed European honey bees (Apis mellifera) have a in Knapp 2010a), and they have also been the negative impact on native bees and that they causal agents of diseases such as chytridiomy- reduce pollination services, decrease the seed cosis, which is implicated in global amphibian set of native plants, and preferentially polli- declines (reviewed in Knapp 2010a). No island- nate the flowers of nonnative plants (reviewed specific data have been collected regarding in Knapp 2010a). Oldroyd (1998) reviewed the their impacts, but bullfrogs occupy reservoirs known methods for controlling honey bees, throughout the island. which include manual hive location or phero - It is widely agreed that bullfrogs are mone lures and insecticide application or extremely difficult to eradicate due to their remote application of insecticide through high fecundity, density dependence, and eva- trained forager bees. Honey bees have been siveness (Schwalbe and Rosen 1988, Lever declining in North America due to a combina- 2003, Adams and Pearl 2007). Eradication and tion of pesticides, parasitic mites, and invasion control methods used to date include electri- of the African honey bee (Sugden et al. 1996); fication of pond water followed by manual and such natural stressors have been used to removal of both adults and larvae; chemical the advantage of honey bee management on and biological control methods; funnel traps; Santa Cruz Island (Wenner et al. 2000). Prior lethal control with air rifles or gigs; and the to this action, honey bee colonies were identi- clearing of vegetation and addition of lime to fied by their foraging patterns and ranges eliminate eggs and tadpoles (Schwalbe and (Wenner and Thorp 1994) then removed by Rosen 1988, Lever 2003). However, popula- closing off all entrances to the colony, induc- tion reductions have been small and short- ing suffocation (after anesthetization; Wenner lived, even in relatively isolated desert ponds et al. 2000). Swarm traps baited with phero - (Schwalbe and Rosen 1988). Results of bull- mones were also used to attract the bees frog population models suggest that they may (Wenner et al. 2000). be most effectively controlled by culling juvenile Habitat restoration could also be practiced frogs in the fall (Govindarajulu et al. 2005) or to moderate the effects of introduced honey with a combination of lethal control of adults bees. Ongoing removal of transformer plants and pond draining at least every 2 years (Dou- used by honey bees, such as fennel (Foenicu- bledee et al. 2003). However, a combination of lum vulgare), yellow star-thistle (Centaurea adult capture, pond drainage, pond excava- solstitialis), and flax-leaf broom (Genista linifo- tion, and capping did not fully eradicate the lia), would remove any facilitation between frogs in one British pond, presumably be - these invasive species. In addition, native cause frogs are able to remain deep in bur- nectar- and pollen-producing plants could rows and vegetation (Lever 2003). be supplemented, particularly those that will 426 MONOGRAPHS OF THE WESTERN NORTH AMERICAN NATURALIST [Volume 7 increase diversity, to ensure that floral Thomas et al. 2006). Alternative approaches resources are not limiting for native species to pesticides include the use of disruptive (e.g., Paton 2001) and to increase native bee hormones and pheromones (Krushelnycky et diversity (Hopwood 2008). Lastly, habitat al. 2002, Suckling et al. 2008). Biological con- clearing and fragmentation could be mini- trol may also be successful, if an appropriate mized, as this favors honey bees (Aizen and natural enemy can be identified (Silverman Feinsinger 1994), and all island landowners and Brightwell 2008). Lastly, bottom-up ap- could adopt a policy that prohibits managed proaches could help favor native taxa over honey bee hives. Argentine ants. Because fragmentation of natu- ral habitat increases the success of Argentine Argentine Ants ants, maintenance of unfragmented habitat Argentine ants (Linepithema humile) are blocks is particularly important to invasion associated with reduced arthropod diversity resistance (Bolger 2007), as is limiting urban and abundance and native bee foraging, as runoff and irrigation (Menke and Holway well as the disruption of mutualistic and para- 2006). sitic relationships (reviewed in Knapp 2010a). Invasive Plants The presence of ants can shift entire food webs and may also impact small mammals, The Conservancy has supported extensive birds, reptiles, and amphibians (reviewed in management of transformer plants. This has Knapp 2010a). On Catalina Island, Argentine involved a thorough mapping of all manage- ants are associated with reduced native ant able invaders then eradication of high-impact, diversity, particularly of endemic species low-abundance species and control of high- (Backlin et al. 2005). There is a large amount impact, high-abundance taxa in priority areas of literature on chemical control methods for (Knapp and Knapp 2005, Knapp 2010b). Argentine ants, particularly in urban settings Treatment along dispersal corridors and pre- and agricultural areas (reviewed in Rust et vention of new introductions are integral com- al. 2003, Soeprono and Rust 2004, Klotz et al. ponents of this effort (Knapp 2010b). In areas 2007). Some eradication attempts have recently of extensive invasion, control could be com- been successful for a variety of invasive ants bined with revegetation efforts to ensure that on islands, including the Argentine ant (re - these areas are not colonized by undesirable viewed in Silverman and Brightwell 2008). species. Integrated vegetation management, Factors that have contributed to the success of which combines invasive plant control with these efforts have been the presence of only native outplantings and manipulation of biotic small, localized infestations; the use of a heli- and abiotic factors that control plant establish- copter to spread bait; and a combination of ment and growth, can be effective (Sheley and techniques, including the removal of alterna- Krueger-Mangold 2003, D’Antonio et al. 2004, tive food sources (Silverman and Brightwell Erskine-Ogden and Rejmánek 2005). 2008). A combination of synthetic trail phero - Nonnative annual grasses are not currently mones and insecticide can also be effective addressed in the Conservancy’s invasive plant (Sunamura et al. 2011). Recently, an experi- management program because they are mental bait distributed in hydrated polyacryl - ubiquitous throughout the island and conse- amide beads has been applied in a trial area on quently difficult to manage. These grasses— Santa Cruz Island with great success and mini - including bromes (Bromus spp.), wild oats mal disturbance (Boser et al. 2014a), and this (Avena spp.), ryegrass (Lolium spp.), barley bait is currently being applied to other loca- (Hordeum spp.), Arabian or Mediterranean tions on the island via helicopter. grass (Schismus spp.), and fescue (Vulpia spp.)— A variety of techniques other than chemical have many deleterious impacts. They hinder means could be investigated to limit Argen- woody plant regeneration; suppress the growth tine ant abundance. Promoting increased ag - of native shrubs, forbs, and perennial grasses; gression within Argentine ant supercolonies shift nutrient cycling regimes; change hydro- by adding individuals of different genotypes logic and geomorphic processes; reduce for- may reduce densities of this social species age quality for small mammals; facilitate insect (Suarez et al. 1999, although see Tsutsui et al. pests and diseases; and promote increased 2003, Buczkowski and Silverman 2006, and fire frequency (reviewed in Knapp 2010a). 2014] ECOSYSTEM RESTORATION ON CATALINA ISLAND 427

Invasive annual grasses cannot be eradi- Water Impoundments cated from the island, but localized control Water impoundments artificially homo- can be accomplished with some effort. A genize water flow regimes, decrease valuable diversity of species and functional groups sediment loads downstream, and alter water will enhance establishment, persistence, and tables, water temperatures, and stream chan- resistance to invasion (Levine 2000, Pokorny nel morphology (reviewed in Knapp 2010a). et al. 2005, Sheley and Half 2006). In particu- The ecological consequences of these effects lar, early-season forbs would best match the can include reduced cover, connectivity, and phenology of the annual grasses and poten- diversity of riparian vegetation; facilitation of tially limit their abundance (Cleland et al. exotic species such as bullfrogs, tamarisk 2013). (Tamarix spp.), and predatory fish; and altera- Roads tion of entire food webs (reviewed in Knapp 2010a). While these impacts have predomi- Roads can impact ecosystem function and nantly been determined in larger river sys- biodiversity by increasing runoff, erosion, tems than those on Catalina Island, even a and stream sedimentation; altering stream portion of these impacts would be cause for flow and duration; reducing and altering habi- concern. The majority of Catalina Island’s tat; increasing wildlife disturbance and mor- watercourses have water impoundments (a tality; promoting invasion of exotic plants and total of 27 impoundments exist: 2 are concrete animals; increasing pollution; promoting fire dams, the remainder are earthen), and some ignition; and forming a barrier to dispersal have several. for smaller species, such as invertebrates, Water impoundment removal has become amphibians, and reptiles (reviewed in Knapp more common worldwide over the past 2 2010a). The fragmentation caused by roads decades in an attempt to restore river and creates extensive stretches of edge habitat that stream processes (e.g., Hansen and Hayes favor invasive wildlife species, such as rats, 2012, Kil and Bae 2012, Renofalt et al. 2013). starlings, Argentine ants, and honey bees Reestablishing natural hydrologic processes (reviewed in Knapp 2010a). Vehicles were the aids in invasive species control and restora- predominant source of island fox mortalities tion in desert river and riparian oak ecosys- during a recovery program for the endangered tems (Stromberg and Chew 2003, Bossard and species (Carlos de la Rosa, Catalina Island Randall 2007). Due to an initial increase in Conservancy, personal communication). sedimentation downstream, macroinverte- Two actions that would minimize the brate richness and densities may actually be effects of roads on Catalina Island are (1) reduced following dam removal (Chiu et al. removing some roads and (2) posting and 2013, Renofalt et al. 2013). However, this enforcing maximum speed laws. Road re - undesirable response diminishes with time, moval is used more and more frequently as a and complete recovery to preimpound states restoration technique (Havlick 2002), but can be achieved after several decades (Hansen few published research studies exist on this and Hayes 2012, Chiu et al. 2013). In addition, technique (Switalski et al. 2004). However, a the abundance of nonnative invertebrate taxa number of road reclamation handbooks exist may be reduced, which could have positive (e.g., wildlandscpr.org). Road restoration typi- food web effects (Cross et al. 2011). Unas- cally involves decompacting, or “ripping,” the sisted recovery rates can vary by proximity to road surface and recontouring hillslopes source populations of native taxa. For exam- (Switalski et al. 2004). Recontouring can ple, benthic invertebrates may only recover accelerate recovery, while simply abandoning when the source populations of desired taxa a road does not recover belowground prop- are found within 5 km of the restoration site erties (Lloyd et al. 2013). Soil amendments (Sundermann et al. 2011). may be added to increase nutrient cycling, and then the area is revegetated (Switalski et Fire al. 2004). Silt fences, check dams, and other Fire is a natural disturbance in Mediter- erosion control structures are used to re- ranean-type ecosystems; however, high fire duce erosion and landslide risk (Switalski et frequency can eliminate woody plants and al. 2004). cause a type conversion to nonnative annual 428 MONOGRAPHS OF THE WESTERN NORTH AMERICAN NATURALIST [Volume 7 grassland (reviewed in Knapp 2010a). Fire size woodlands but would also put invasive bull- has been increasing on Catalina Island over frogs and tamarisk at a disadvantage. In both the last century, and the fire season has been cases, native wildlife species would be pro- expanded (Catalina Island Conservancy, un - vided the maximum natural resources possible published data). Given that fires are exceed- and given the best chance of successfully com- ingly difficult to prevent and control, the only peting with or evading predation by invasive ways to limit the recurring frequency of fire animals, such as cats, that cannot be other- on the island are to minimize ignitions to the wise managed. This concept has been called extent possible and continue to manage burns “bottom-up invader management” (D’Antonio as they occur. Strategies could include limit- and Chambers 2006) and is an appealing alter- ing human use of high-risk areas and con- native on a degraded island such as Catalina ducting prefire planning (Keeley 2002). Island where eradication of some transforma- Although a draft fire management plan has tive invasive species is unlikely. been produced (“Firewise 2000” 2003), it Mule deer have a strong negative impact advocated prescription burning as a means for on the island’s biota; their eradication would preventing large wildfires. This type of mosaic be technically feasible but would require a rotational burning may not be appropriate for change in state law. Bison have similar negative the habitat types and conditions on Catalina effects on woody plant species but may also Island (Moritz 2003, Keeley and Zedler 2009). have the positive effect of controlling exotic In addition, slope stability is of concern fol- annual grasses and are an important ecotourism lowing a burn (Keeley 2004). Rotational burn- attraction. Perhaps deer removal would reduce ing may also degrade shrublands by increasing the pressure on woody plant species enough the fire frequency (Zedler and Seiger 2000, that the effects of bison would be less critical. Keeley 2002). An updated, ecologically sound Deer removal would have the additional bene- fire management plan is necessary, and it fit of recovering plant cover and structural should identify wildland areas that have diversity, which would further decrease the recently burned or in which a new burn would disturbance and fragmentation that favors have particularly detrimental effects, as well other invaders, both plant and animal. as potential defense locations and preferred For most other invaders, including cats, burn perimeters. The plan could be used by rats, bullfrogs, starlings, cowbirds, and Argen- island firefighters and the Conservancy to tine ants, successful eradication is unlikely for quickly identify priority areas for wildland fire both logistical and social reasons. Bottom-up control in the event of an ignition. To be invader management might be the best way effective, however, the plan must be adopted to disadvantage those species and, equally by island fire officials and updated regularly. important, to support healthy populations of native wildlife that are better able to with- DISCUSSION stand their effects. As an example, ground squirrels may be depredated by feral cats. While there are many constraints to ecosys- However, ground squirrel populations are tem restoration on Catalina Island (not the more limited by bottom-up factors, such as least of which are high human visitation and burrow site availability and food plant abun- public opposition to control of some invasive dance (Van Horne 2007), than by the presence animals), this review highlights a number of of predators (Byrom et al. 2000). Increasing opportunities as well, with a potential myriad the amount of food and habitat available to the of cascading positive effects. Removing and squirrels may counter some population effects revegetating selected roads would not only of predation by feral cats. reduce fragmentation, erosion and stream sedi- In contrast to these other species, Euro- mentation, road kill, pollution, and fire igni- pean honey bees could feasibly be eradicated, tion, it may also disadvantage invaders such as as has been accomplished on nearby Santa rats, Argentine ants, honey bees, starlings, and Cruz Island. Island-specific data regarding Brown-headed Cowbirds in those areas. Simi- their impacts and ecological interactions, as larly, restoring natural stream flow regimes by well as their distributions, would help to both removing dams and revegetating waterways justify and prepare for such an undertaking. would not only enhance riparian and oak Even if impacts have not been determined, 2014] ECOSYSTEM RESTORATION ON CATALINA ISLAND 429 eradication of potentially harmful introduced genetic variation necessary to become more species can be justified under what is called successful (Suarez and Tsutsui 2008). Catalina the “precautionary principle” (IUCN 2000, Island is no stranger to the risks of intro - Clergeau et al. 2004, Hulme 2006). This same duced pathogens, as the island fox population reasoning could be applied to the eradication declined by 95% after exposure to canine dis- of the wild turkey. temper virus (Timm et al. 2009). Continued diligence is important to ensure Extensive education and outreach efforts are the long-term success of the Conservancy’s needed to obtain the community support that invasive plant management program, as is critical to the success of invasive species aboveground populations are eliminated but prevention, eradication, and control programs seed banks remain. Maintaining such commit- (IUCN 2000, Morrison et al. 2011). Legal ment when the problem is visually reduced is action may sometimes be required (Myers et one of the main challenges to successful plant al. 1998). Although conservation efforts on eradication (Mack and Lonsdale 2002). Peri- Catalina Island are constrained by many fac- odic remapping should be undertaken to tors, some of those same constraints are also accomplish early detection of and rapid response key assets. The high level of visitation to Cata - to new invaders and reemerging species from lina makes it an ideal educational and out- seed banks. Aerial surveys are a powerful, reach center for the southern Channel Islands. low-impact tool for detecting small popula- The Conservancy’s Nature Center and Botani- tions of new invaders (Mack et al. 2000). Heli- cal Garden provides a venue for outreach copter transport can also be used very effec- regarding the uniqueness of the islands, the tively to remove remote infestations of trans- threats that face them, and the benefits of former plants (Knapp et al. 2011). Further, restoration. The island’s residents also gain from expanded invasive plant control combined the Conservancy’s conservation actions in the with native outplantings would not only bene- form of ecotourism dollars (Wilson 2000). fit native biodiversity but may also disfavor In conclusion, although ecosystem restora- European honey bees. tion of Catalina Island will not be quick, The order of any management actions under- cheap, or easy, the potential returns in eco- taken by the Conservancy should take into logical resilience may be substantial. Given account cascading trophic effects and the need real logistical and social constraints on some for access in order to avoid unintended conse- restoration options, the managers of Santa quences (Zavaleta et al. 2001, Morrison 2011). Catalina Island might best pursue options that As a hypothetical example, if cats and rats were will enhance this resilience from the bottom to be excluded from a limited area, this should up. By restoring natural hydrologic processes happen first while the vegetation is degraded and habitat connectivity, native species would and open and trapping is more feasible. Dam re- be favored over invaders that benefit from moval and mule deer eradication would initi- fragmentation, altered disturbance regimes, ate substantial vegetation recovery and should and reduced biodiversity. Combined with logically occur after removal of cats and rats. expanded efforts to educate the public about Lastly, selected roads should be removed only these threats and to prevent future nonnative when this access is no longer needed. species introductions, the island could be a Considering the high risk of additional model for management of altered ecosystems. future introductions and the complexity of eradication and control programs, prevention ACKNOWLEDGMENTS should be one of the highest priorities for future conservation efforts on Catalina. It is John Knapp and Darcee Guttilla were widely agreed that the most desirable sce- invaluable in providing information, brain- nario is to prevent species introductions storming sessions, and editorial comments that before they occur (e.g., IUCN 2000, Rejmánek greatly improved the paper. Peter Schuyler and and Pitcairn 2002, Courchamp et al. 2003); Carla D’Antonio also reviewed prior versions therefore, biosecurity measures are needed of this work and provided helpful feedback. (e.g., Boser et al. 2014b). Even species that This paper was also vastly improved through are already present, such as rats, could either the suggestions of 3 anonymous reviewers and introduce deadly new pathogens or gain the the journal’s editors. 430 MONOGRAPHS OF THE WESTERN NORTH AMERICAN NATURALIST [Volume 7

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