Landscape of coastal sage scrub, grasslands, and chaparral
Coastal Sage Scrub Restoration

 

Coastal sage scrub is one of the United States’ most imperiled ecosystems. This plant community is composed of a diverse array of drought-tolerant plant species, including drought-deciduous shrubs such as California sagebrush (Artemisia californica) and several true sage species (Salvia species). Other evergreen shrub species, perennial bunchgrasses, and annual and perennial forbs are also important constituents of this ecosystem, all of which contribute to its rich biodiversity [1]. Once covering vast coastal regions from Baja California in the south, north to the Bay Area, much has been lost to urban development, historic grazing, and other land use changes. A significant portion of these shrublands have been converted to invasive annual grasslands due in large part to increased wildfire frequency driven by these invasives which easily ignite and spread fire [2]. In southern California, high levels of nitrogen deposition from air pollution leads to increased soil nitrogen availability, which favors invasive annuals and may severely reduce native plant diversity [3].

Given the severely threatened status of this biodiverse ecosystem and the important wildlife habitat it provides (including for the endangered California gnatcatcher), much attention has been devoted to its restoration. Success, however, is severely limited by a number of factors, including weed pressure, drought, altered fire regimes, limited availability of native propagules, nitrogen deposition, and resource constraints [4]. As with many other ecosystems in California, controlling invasive weeds is a critical first step for successful restoration, as these fast-growing species can outcompete establishing seedlings. Methods include nonchemical manual or mechanical removal [5], targeted herbicide application [6], and managed grazing [7], all of which can aid in reducing the abundance of invasive species. Soil solarization and prescribed fire can also be effective tools for reducing weed pressure before reintroducing native species [8].

Most restoration of this ecosystem focuses on establishing native shrub species such as California sagebrush (Artemisia californica), sage species (e.g., Salvia apiana, S. leucophylla, and S. mellifera), California brittlebrush (Encelia californica), and California buckwheat (Eriogonum fasciculatum). This can be accomplished through seeding or outplanting of nursery grown seedlings. Transplanted individuals tend to have higher survival rates and achieve greater biomass more quickly than those established from seed, but this method is more costly and resource-intensive. Seeding is a more cost-effective approach over large areas, but success can be highly variable depending on the rainfall year. Native forbs are an important component of coastal sage scrub communities, but seeding these along with perennials can reduce growth and establishment of shrubs due to competitive interactions [9]. Seeding forbs in separate subplots or delaying their introduction until shrubs are well established may be the most effective strategy for restoring herbaceous communities while prioritizing the successful establishment of shrubs.

Active restoration is essential for severely disturbed sites where native propagules are absent in the soil seed bank or nearby remnant populations. However, in some cases, native shrubs can naturally recolonize, and passive restoration, following targeted weed control, has proven to be highly effective at certain sites [10].

Resources

References

  1. Cleland, E. E., Funk, J. L., & Allen, E. B. (2016). Coastal sage scrub. Ecosystems of california, 429-448. https://www.jstor.org/stable/10.1525/j.ctv1xxzp6
  2. Cox, R. D., Preston, K. L., Johnson, R. F., Minnich, R. A., & Allen, E. B. (2014). Influence of landscape-scale variables on vegetation conversion to exotic annual grassland in southern California, USA. Global Ecology and Conservation, 2, 190-203. https://doi.org/10.1016/j.gecco.2014.09.008
  3. Valliere, J. M., Bucciarelli, G. M., Bytnerowicz, A., Fenn, M. E., Irvine, I. C., Johnson, R. F., & Allen, E. B. (2020). Declines in native forb richness of an imperiled plant community across an anthropogenic nitrogen deposition gradient. Ecosphere, 11(2), e03032. https://doi.org/10.1002/ecs2.3032
  4. Allen, E. B., McDonald, C., & Hilbig, B. E. (2019). Long-term prospects for restoration of coastal sage scrub: invasive species, nitrogen deposition, and novel ecosystems. Proceedings of the chaparral restoration workshop, California. Gen. Tech. Rep. PSW-GTR-265. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 1-18. PDF
  5. DeSimone, S. A. (2013). Restoration and science: A practitioner/scientist's view from rare habitat restoration at a southern California preserve. Restoration Ecology, 21(2), 149-152. https://doi.org/10.1111/j.1526-100X.2012.00923.x
  6. Bell, C. E., Allen, E. B., Weathers, K. A., & McGiffen, M. (2016). Simple approaches to improve restoration of coastal sage scrub habitat in southern California. Natural Areas Journal, 36(1), 20-28. https://doi.org/10.3375/043.036.0107
  7. Kimball, S., Lulow, M., Sorenson, Q., Balazs, K., Fang, Y.-C., Davis, S.J., O'Connell, M. and Huxman, T.E. (2015), Cost-effective ecological restoration. Restoration Ecology, 23: 800-810. https://doi.org/10.1111/rec.12261
  8. Moyes, A. B., Witter, M. S., & Gamon, J. A. (2005). Restoration of native perennials in a California annual grassland after prescribed spring burning and solarization. Restoration Ecology, 13(4), 659-666. https://doi.org/10.1111/j.1526-100X.2005.00084.x
  9. Bell, M. D., Lulow, M. E., Balazs, K. R., Huxman, K. A., McCollum, J. R., Huxman, T. E., & Kimball, S. (2019). Restoring a Mediterranean‐climate shrub community with perennial species reduces future invasion. Restoration Ecology, 27(2), 298-307. https://doi.org/10.1111/rec.12851
  10. DeSimone, S. A. (2011). Balancing active and passive restoration in a nonchemical, research-based approach to coastal sage scrub restoration in southern California. Ecological Restoration, 29(1-2), 45-51. https://doi.org/10.3368/er.29.1-2.45