USDA Forest Service

Pacific Southwest Research Station
Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
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Research Topics Fire Science

Post-fire shrub growth in conifer ecosystems

Small shrubs grow in the foreground with ponderosa pine trees in the background.
Three years after a fire, a resilient stand of ponderosa pine with a diverse understory including a shrub component develops on the Tahoe National Forest. Photo by Jens Stevens, University of California, Davis)

After a fire in Sierra Nevada conifer forests, a variety of shrubs and herbaceous species often regrow to take advantage of higher light levels and open soil conditions. Predominant  shrub species include Ceanothus (deerbrush, snowbrush, mahala mat) and Arctostaphylos (various manzanitas). Bear clover (Chamaebatia foliolosa, also known as mountain misery), a shrub, will reappear in abundance where it occurred before the fire. If a seed source is available, conifer seedlings will begin to establish and grow among the shrubs, though they may not be visible to the casual observer initially.

Shade produced by trees normally limits growth of understory shrubs, but when those trees are killed by a high severity fire, abundant shrub growth can result in a stand of montane chaparral that persists for many years. While these shrubs can initially limit the growth of tree seedlings by competing with them for light and soil moisture, many shrub species, especially Ceanothus, harbor beneficial bacteria in their roots which help to enrich the soil with nitrogen and can also enhance the growth of conifer seedlings. In 20 to 40 years, conifer seedlings can grow tall enough to start shading the shrubs, and the ecosystem will eventually progress to a conifer forest where shrubs exist only as scattered individuals and a seed bank in the soil, waiting for the next fire.

If a hot fire burns through the regrowing shrub and conifer sapling stand, young trees may be killed, resulting in further persistence of the chaparral. Due to fire suppression in Northern California, many historic chaparral patches have been over-topped and shaded out by firs and other conifers. In other areas, recent large fires with extensive high-severity patches could result in much larger montane chaparral areas where conifer seeds may not become established for many decades.

Management considerations

Long-term shrub dominance can be undesirable where land was previously used for recreation or timber production prior to fire, so land managers may choose to reduce shrub cover to speed conifer regrowth. When shrub competition is removed, planted conifers, such as ponderosa pines grow faster, especially in stands less than 20 years old, but this advantage is lost once the stand canopy closes. Managers of private timberlands may overcome the loss of nitrogen from shrub-root bacteria contributions with artificial fertilization.

Publications and references:
  • Bock, J.H.; Raphael, M.; Bock, C.E. 1978. A comparison of planting and natural succession after a forest fire in the northern Sierra Nevada. Journal of Applied Ecology. 15: 597-602.
  • Busse, M.D.; Cochran, P.H.; Barrett, J.W. 1996. Changes in ponderosa pine site productivity following removal of understory vegetation. Soil Science Society of America Journal. 60: 1614-1621.
  • Collins, B.M.; Roller, G.B. 2013. Early forest dynamics in stand-replacing fire patches in the northern Sierra Nevada, California, USA. Landscape Ecology. 28: 1801-1813.
  • Conard, S.G.; Jaramillo, A.E.; Cromack, K. Jr.; Rose, S., comps. 1985. The role of the genus Ceanothus in western forest ecosystems. Gen. Tech. Rep. PNW-182. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 72 p.
  • Knapp E.E.; Weatherspoon, C.P.; Skinner, C.N. 2012. Shrub seed banks in in mixed conifer forest of Northern California: implications for managing shrub abundance with fire. Fire Ecology. 8(1): 32-48.
  • Long, J.W.; Skinner, C.; Charnley, S.; Hubbert, K.; Quinn-Davidson, L.; Meyer, M. 2014. Post-wildfire management. In: Long, J.W.; Quinn-Davidson, L.; Skinner, C.N., eds. Science synthesis to support socioecological resilience in the Sierra Nevada and southern Cascade Range. Gen. Tech. Rep. PSW-GTR-247. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 187-220. Chap. 4.3.
  • Nagel, T.A.; Taylor, A.H. 2005. Fire and persistence of montane chaparral in mixed conifer forest landscapes in the northern Sierra Nevada, Lake Tahoe Basin, California, USA. Journal of the Torrey Botanical Society. 132: 442-457.
  • Russell, W.H.; McBride, J. 1998. Revegetation after four stand-replacing fires in the Lake Tahoe basin. Madroño. 45: 40-46.
  • Skinner, C.N.; Taylor, A.H. 2006. Southern Cascades bioregion. In: Sugihara, N.G.; van Wagtendonk, J.W.; Fites-Kaufman, J.; Thode, A.E., eds. Fire in California’s ecosystems. Berkeley, CA: University of California Press: 195-224.
  • van Wagtendonk, J.W.; Fites-Kaufman, J. 2006. Sierra Nevada bioregion. In: Sugihara, N.G.; van Wagtendonk, J.W.; Fites-Kaufman, J.; Thode, A.E., eds. Fire in California’s ecosystems. Berkeley, CA: University of California Press: 264-294.
  • Zhang, J.; Powers, R.F.; Oliver, W.W.; Young, D.H. 2013. Response of ponderosa pine plantations to competing vegetation control in northern California, USA: a meta-analysis. Forestry. 86: 3-11.
Last Modified: Dec 19, 2016 02:56:31 PM