Simple Approaches to Improve Restoration of Coastal Sage Scrub Habitat in Southern California Author(S): Carl E
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Simple Approaches to Improve Restoration of Coastal Sage Scrub Habitat in Southern California Author(s): Carl E. Bell, Edith B. Allen, Kristin A. Weathers and Milton McGiffen, Jr., Source: Natural Areas Journal, 36(1):20-28. Published By: Natural Areas Association DOI: http://dx.doi.org/10.3375/043.036.0107 URL: http://www.bioone.org/doi/full/10.3375/043.036.0107 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. R E S E A R C H A R T I C L E ABSTRACT: Much of the coastal sage scrub habitat in Southern California that existed prior to European settlement has been developed for human uses. Over the past two to three decades, public agencies and land conservation organizations have worked to acquire some of the remaining lands for preservation. Many of these lands are degraded by past intensive livestock grazing, farming, and frequent fires, and the native flora has been replaced by weedy, exotic annual grasses and forbs, mostly of Mediterranean origin. Restoration of native flora is challenging and there are few successful examples to provide guid- • ance on effective methods. Cost is also an important and prohibitive factor. Competition from weeds is one of the most difficult impediments to establishing native vegetation, which often persists in the Simple Approaches seedbank. We compared annual applications of the nonselective herbicide glyphosate over multiple years, followed by a final year with the grass-specific fluazifop, as a simple, low cost method of reducing the exotic seedbank sufficiently to allow native vegetation to establish. This approach was combined with to Improve seeding native forbs, herbaceous perennials, and shrubs in one half of each treatment plot. Herbicide treatments were made in the spring each year from 2006 to 2010, and were combined with weed trim- ming in 2010 and 2011 to remove exotic forb inflorescences, and raking to remove litter. In 2010, native Restoration of plant cover in herbicide-treated plots was about 50%, consisting of 43 species, compared to <5% cover in the control plots. Most of the native plants came from the existing seedbank, and very few from the Coastal Sage Scrub seed mix. A cost analysis showed that a once-yearly herbicide treatment was as effective as one ap- plication plus spot spraying or hand inflorescence trimming, and is more cost-effective than hand weed Habitat in Southern control and raking for restoration. California Index terms: coastal sage scrub, fluazifop, glyphosate, herbicide, weeds INTRODUCTION Spanish colonists in the late 18th century introduced extensive livestock grazing, and Coastal sage scrub (CSS) is a Mediter- management practices through the early 1,3 Carl E. Bell ranean-type floristic community in lower 20th century often included intentional 1University of California elevation California and northern Baja Cali- fire to burn off scrub and encourage forage Cooperative Extension fornia, Mexico (Rundel 2007). In southern (Burcham 1957). Most lands within the San Diego, CA California, it occurs in a coastal band from range of CSS that were level enough to Santa Barbara on the north to San Diego till were converted to agriculture or pasture in the south and inland to the Riverside before the first statewide vegetation survey area. CSS vegetation is diverse and spe- of the 1930s (Vegetation Type Map; Cox Edith B. Allen2 cies rich, but typically dominated by a few et al. 2014). Some of these lands have 2 Kristin A. Weathers shrub species, such as Artemisia californica more recently been converted to housing Milton McGiffen, Jr.2 Less., Eriogonum fasciculatum Benth., developments (Chen et al. 2010), as CSS Salvia mellifera Greene, S. leucophylla includes the most desirable coastal lands for Greene, and Rhus integrifolia (Nutt.) Rothr. urban expansion. The result is the signifi- 2 University of California (Weaver and Clements 1938; Rundel 2007). cant loss of CSS vegetation. Estimates of Department of Botany and Rainfall is limiting throughout this range, presettlement CSS that has been converted Plant Sciences averaging 450 mm in the northern extent to agriculture, urban development, and Riverside, CA to 250 mm in the south and inland regions. exotic annual grassland vary from 40 to Rain falls sporadically and unpredictably 90% (Westman 1981; Cleland et al. 2016). from fall through spring, followed by a The quality of remaining CSS communities • summer drought of five or more months varies considerably; estimates suggest that (Dallman 1998). Several of the dominant 50% of the remaining habitat is degraded species are drought deciduous, including by frequent wildfires, invasive plants, air 3 Corresponding author: A. californica and the Salvia species. Other pollution, and other causes (Freudenberger [email protected]; (760) 815-2777 dominant species exhibit sclerophyllous et al. 1987; Allen et al. 2000; Cleland et leaves, small leaves, are succulents, or al. 2016). have extensive root systems. CSS has one of the highest concentrations European settlement of California resulted of federally listed and rare species in the in extensive loss of CSS and conversion United States, and is considered one of to exotic annual grassland (Minnich and the most threatened ecosystems in the Natural Areas Journal 36:20–28 Dezzani 1998; Allen et al. 2000; Talluto and country (Noss et al. 1995). In an effort to Suding 2008; Fleming et al. 2009). Early preserve CSS, government agencies and 20 Natural Areas Journal Volume 36 (1), 2016 private conservancies have been acquir- the native seed density was only 400 Loam—a deeper soil, 50 to 100 cm above ing land as part of habitat conservation seeds/m2 (Cox and Allen 2008a). If seed bedrock, and a water availability capacity plans to prevent urban development (Scott inputs to the soil are stopped, the weed of 18 cm. Elevation at both sites is about et al. 2006). Some of this CSS habitat is seed bank declines rapidly (Radosevich 450 m. Mean precipitation is 414 mm per undergoing restoration because the native et al. 2007). Our restoration research was season (July 1 to June 30), but seasonal vegetation has been replaced by exotic designed to determine how different levels variation over the years of this research was annuals. Former cattle ranches are typi- of invasive weed control would influence 152 mm in the 2006/07 season, 371 mm cally the largest contiguous properties that establishment from the native seedbank of in 2007/08, 285 mm in 2008/09, and 441 have conservation value, but also include CSS (Allen et al. 2001). For comparison, mm in 2009/10, accompanied by consid- degraded lands. For example, the County we included a subplot treatment of seed- erable in-season variation (CIMIS 2014). of San Diego Barnett Ranch Reserve near ing native forbs and shrubs to enhance the The site has relatively low anthropogenic the city of Ramona, California, where native seedbank (Allen et al. 2001). Weed nitrogen deposition (~6 kg N ha-1 yr-1, we conducted our research, was used by control was done annually using herbicides Fenn et al. 2010). Mission San Diego for cattle grazing in to reduce additions to the weed seed bank the mid-eighteenth century. The County while allowing depletion of the existing Our research utilized a split-plot design bought the property in 2002 to become seed. An adaptive management approach with three treatments at each of the two part of the County Multi-Species Conser- was used to control different weed life sites. Herbicide was the main plot treat- vation Plan, a habitat conservation plan forms as the community developed over ment, applied to plots 6 × 18 m with five designed to satisfy mitigation concerns time. To encourage establishment of the replications per treatment. Treatments regarding development and endangered native community of forbs and shrubs, were; (1) herbicide applied once each species (Helix Environmental Planning the broad-spectrum herbicide used ini- spring broadcast over the whole plot (here- 2004). The entire 294-ha reserve burned tially was substituted by a grass-specific after Herbicide 1X), (2) herbicide applied in a wildfire in November 2003. Although herbicide after three years. At this point, broadcast once in the spring followed the property was purchased for its na- inflorescences of exotic forbs were trimmed by spot spraying weeds as needed that tive habitat value, approximately 95 ha manually to reduce their contribution to emerged after the initial treatment (here- is dominated by weedy exotic grasses the seedbank. If successful, this would after Herbicide 2X), and (3) an unsprayed and forbs (Helix Environmental Planning be a simple, relatively low cost approach control plot (hereafter control). Broadcast 2004). The presettlement habitat of this that could be adopted by land managers herbicide applications were made in Febru- land is unknown, but based on fragments in Southern California. ary or March each year depending upon of remnant vegetation it is likely that it exotic plant emergence following winter had been a mix of CSS, native perennial METHODS rains. Broadcast herbicide applications grassland, and native annual forb fields were made with a hose-end sprayer with a (Helix Environmental Planning 2004).