SANTA CATALINA ISLAND EXPERIMENTAL RESTORATION TRIALS: DEVELOPING APPROPRIATE TECHNIQUES LISA C. STRATTON 525 Lorraine Ave., Santa Barbara, CA 93110; [email protected] Abstract—Since 1999 the Catalina Island Conservancy has implemented eleven native plant restoration trials on 34 ha of abandoned agricultural fields in Middle Canyon on Santa Catalina Island. The trials were designed to evaluate the extent to which native plant communities can be established within weedy fields without intensive human inputs. Through an iterative series of native plant restoration trials we have found that non-native plants (weeds) and animals (deer [Odecoileus hemionus] and bison [Bison bison]) have a greater impact on the site than expected. Annual weed control, adding propagules (e.g., seeds) and planting seedlings without protection are insufficient to tip the balance in favor of native plants. These conclusions are reflective of the heavily disturbed old agricultural field conditions of Middle Canyon and will be applicable to other disturbed sites where we may want to do restoration on Catalina Island. Subsequent trials that took those limitations into consideration (e.g., more frequent weed control and planting seedlings into protected conditions) provided species-specific information about growth rates, water requirements and survivorship that will make subsequent restoration efforts much more efficient and appropriate. The specific trials cover a variety of native plant communities including native bunch grass, coastal sage scrub, chaparral, oak woodland and ephemeral streamside ‘riparian’ plant communities. The primary conclusions from each trial are described in this paper. Keywords: chaparral, coastal sage scrub, oak, restoration, Santa Catalina Island INTRODUCTION conclusion from these authors was that ‘passive,’ wait and see strategies were not suitable for Very little native plant restoration work on the restoring coastal sage scrub and chaparral plant Channel Islands has been published, particularly communities on disturbed sites in southern the southern Channel Islands (O’Malley 1991). On California. Research has demonstrated that exotic Santa Cruz Island restoration efforts have focused disturbance (e.g., plowing) can alter successional on strategies for removing dense stands of fennel processes and can lead to the persistence of early (Foeniculum vulgare) and on Santa Barbara Island seral stage plant communities or weed-dominated the National Park Service worked on restoring landscapes (Stylinski and Allen 1999). As such, eroded sites with weed cloth and seeding when the opportunity came to restore the disturbed (Halvorson 1993). During the 1990s in southern fields in Middle Canyon, we knew that we not only California, coastal sage scrub restoration was the had to do more than wait and see if adjacent native subject of several studies and restoration and plants would colonize the site, but also work to mitigation projects (Bowler 1990, Marquez and reduce the risk that this population of non-native Allen 1996, Eliason and Allen 1997). These studies plants would serve as a source for invasion into demonstrated that annual grasses and legumes adjacent intact native areas. reduced biodiversity and limited natural The Santa Catalina Island Conservancy, regeneration of native species in disturbed coastal established in 1972, assumed ownership of 88% of sage scrub sites. Nitrogen deposition, Santa Catalina Island in 1975. Initial management fragmentation and isolation from stands of native efforts focused on maintaining the ranching and hay vegetation (e.g., seed sources) also reduced the farming activities in Middle Canyon. In the mid- biodiversity and regenerative capacity of coastal 1990s, however, the Conservancy began to engage sage scrub species (Allen et al. 1998). The in active conservation including removal of non- 214 STRATTON native pigs and goats and restoration of degraded sites. In 1998 we wrote a restoration plan and in 1999 initiated restoration trials on the 34 ha of old agricultural fields (Stratton 1998). While over eleven restoration trials were established over a four-year period, this paper will concentrate on four mm of those trials and describe how they arose from previous trials and elaborate on the implications of their results. The primary challenges to restoration of native plant communities in Middle Canyon on Catalina Island were browsing and trampling by deer (Odecoileus hemionus) and bison (Bison Figure 1. Annual precipitation Middle Canyon, Santa Catalina bison), competition by weeds, unpredictable Island, July 1992 to June 2004. Dotted line reflects mean rainfall and altered soil conditions. The trials were annual precipitation since 1948. designed to address these concerns while also minimizing maintenance requirements. These trials Oak Watering Trial represent experimentation with 6,500 seedlings and The oak watering trial, established in 1999, 1.5 million seeds of 48 species from five plant was designed to test three different watering communities: native bunch grass, oak woodland, options and whether or not the addition of soil coastal sage scrub, chaparral and ephemeral stream components collected under mature trees and ‘riparian’ vegetation. added to planted seedlings contributed to success. Because no research had been done on the island on the water requirements of our endemic oaks MATERIALS AND METHODS (Quercus pacifica), we decided to test the value of some strategies used in arid environments to Site Description provide water only to the roots of the tree. The project site, Middle Canyon, is a broad Research on central valley oaks, where rainfall is canyon in the central portion of Santa Catalina higher, had already demonstrated that competition Island at 215 m elevation which was leveled and for moisture from weeds reduced growth and used to grow oats for over 50 years. The 34 ha of survivorship of oaks, so there was the possibility old agricultural fields are bisected by a dry stream that island oaks would require more water bed with some mixed ‘riparian’ vegetation, (McCreary and Tecklin 1997). We directed water however most of the side streams have been filled to the roots of the tree via a vertical pipe installed in. The site is surrounded on the north by south- adjacent to the seedling or with ‘driwater,’ a slow facing slopes dominated by coastal sage scrub and release polymer that releases water as bacteria on the south, by steep north facing slopes with break down the globules, in order to promote deep oaks, mixed chaparral and disturbed annual root growth without encouraging surface weed grassland vegetation. The vegetation in the old growth (Sawaf 1980, Mathew 1987, Bainbridge agricultural fields is dominated by Bromus and Virginia 1989). The driwater product was diandrus, Bromus hordeaceus, Avena fatua, Vulpia selected because it can last up to three months and myuros, Sysimbrium officionale, Raphanus conformed to our policy of selecting techniques vulgare, Medicago polymorpha, Meliotis indica that reduce human intervention and effort relative and scattered stands of Foeniculum vulgare, to monthly hand irrigation. Twelve plots of 14 Marrubium vulgare and Phalaris aquatica. The seedlings each of Quercus pacifica were planted in soil is deep, silty, gray clay. Average rainfall for January 1999. Four plots each were randomly the period 1948 to the present is 325 mm/year. assigned to one of three watering treatments: Three out of the last five years have been below “Driwater” at the root zone for 2.5 years during the average rainfall (Fig. 1). Precipitation follows the dry months, monthly deep pipe watering to the root Mediterranean pattern and falls from late zone (4 L/month) or no additional watering December through March. (controls). NATIVE PLANT RESTORATION 215 The second factor of the trial, importance of sprouts. On a longer time frame, the eight plots of 50 adding native soil from mature oaks, was crossed planting sites were arranged topographically at the with the initial factor by adding soil to every other mouth of (four plots) and adjacent to (four plots) seedling in each plot. Many studies have side canyons feeding into a larger field in order to demonstrated that the presence of appropriate evaluate whether there were any subterranean water microbial symbionts in the soil can greatly improve patterns that the oaks would respond to. The fields the nutrient status and plant performance of many had been leveled so there were no visible side native species (Aldon 1978, Trappe 1981, Read et streams from the side canyons feeding into the main al. 1985, St. John 1985, Bloss 1986). Plants can be stream bed; however we thought that the leveled inoculated by adding soil from mature individuals fields may disguise underlying water patterns. We of the same or similar species in their native habitat do not expect the trees to reveal these differences for (Schiechtl 1980, Bainbridge and Virginia 1989). many years until the roots are deep enough. All Because the fields had such a long history of planting sites had a tree tube surrounded by a 1-m2 disturbance there was a chance that the native soil weed mat to funnel water to the ground. Acorns biota had been destroyed. Adding native soil to the were planted in January 2001 and height and root zone at the time of planting was a survivorship were monitored in the spring and fall. straightforward way of evaluating the potential Data were analyzed with two-way ANOVA benefits of inoculation on oaks which are known to analyses on