Wildlowers in grassland
Grassland Restoration

 

California's grasslands cover over 10% of the state's land area and are distributed across a range of elevations and climates, from coastal prairies to inland valleys [1]. This includes diverse community types such as annual grasslands, perennial grasslands, and mixed woodland and shrubland-grassland systems [2]. California grasslands are vital ecosystems that support biodiversity, provide wildlife habitat and forage for livestock, and play a key role in carbon sequestration. However, the state’s grasslands are one of the most heavily impacted and degraded ecosystems due to human activities, and they face significant threats, including habitat loss due to agriculture and urbanization, nonnative plant invasion (particularly of invasive annual grass species), altered hydrology, and the impacts of climate change.

Given how degraded many grasslands in the State are, restoration is critical for maintaining the health and functionality of these ecosystems. Land managers throughout California have developed a variety of approaches for advancing successful grassland restoration [3]. These efforts typically involve the removal of invasive species, reintroduction of native plants (through seeding and outplanting), management of grazing practices, and prescribed fire [4]. Controlling invasive annual grasses and other weeds is often required for successful native plant establishment. This can be accomplished through herbicides or carefully timed treatments of grazing [5], prescribed fire, [6] or mowing [7], though multiple years of treatment may be required to deplete the soil seedbank. These approaches can shift the balance from invasive annuals to native perennial bunchgrasses as long as remnant natives are present, and weed management will require continued effort during the restoration process. Complete eradication of annual grasses is often infeasible, and efforts instead should focus on reducing competition in order to reestablish natives.

Restoration of native bunchgrasses can be accomplished through seeding or transplanting. Transplanting plugs can be highly effective for establishing perennial plants, but this is more expensive and resource intensive than seeding and may not be feasible at larger spatial scales. Plugs should be planted during the winter months when precipitation occurs, but irrigation can widen this window of opportunity. Seeding can be done through hand broadcasting or using specialized equipment such as drill seeding or hydroseeding. Native forbs are an important component of grasslands, and these must be seeded into restoration sites. These fast growing species can reduce growth and survival of native perennials if sown at the same time [8], so in some instances waiting to introduce native forbs until after perennials are established may be the best approach for restoring functionally diverse plant communities.

Resources

References

  1. Huenneke, L. F. (1989). Distribution and regional patterns of Californian grasslands. In Grassland structure and function: California annual grassland (pp. 1-12). Dordrecht: Springer Netherlands. https://doi.org/10.1007/978-94-009-3113-8_1
  2. Barbour, M., Keeler-Wolf, T., & Schoenherr, A. A. (Eds.). (2007). Terrestrial vegetation of California. Univ of California Press. https://www.jstor.org/stable/10.1525/j.ctt1pnqfd
  3. Luong, J. C., Press, D. M., & Holl, K. D. (2023). Lessons learned from an interdisciplinary evaluation of long-term restoration outcomes on 37 restored coastal grasslands in California. Biological Conservation, 280, 109956. https://doi.org/10.1016/j.biocon.2023.109956
  4. Stromberg, M. R., D’antonio, C. M., Young, T. P., Wirka, J., & Kephart, P. R. (2007). California grassland restoration. California grasslands: ecology and management. University of California Press, Berkeley, 254-280. PDF
  5. Menke, J. W. (1992). Grazing and fire management for native perennial grass restoration in California grasslands. Fremontia, 20(2), 22-25. PDF
  6. Keeley, J. E., Klinger, R. C., Brennan, T. J., Lawson, D. M., La Grange, J., & Berg, K. N. (2023). A decade‐long study of repeated prescription burning in California native grassland restoration. Restoration Ecology, 31(7), e13939. https://doi.org/10.1111/rec.13939
  7. Valliere, J. M., Balch, S., Bell, C., Contreras, C., & Hilbig, B. E. (2019). Repeated mowing to restore remnant native grasslands invaded by nonnative annual grasses: Upsides and downsides above and below ground. Restoration Ecology, 27(2), 261-268. https://doi.org/10.1111/rec.12873
  8. Young, T. P., Zefferman, E. P., Vaughn, K. J., & Fick, S. (2015). Initial success of native grasses is contingent on multiple interactions among exotic grass competition, temporal priority, rainfall and site effects. AoB Plants, 7, plu081. https://doi.org/10.1093/aobpla/plu081