Definitions

basic assumption

Chaparral

[shap-uh-ral, chap-]

Chaparral is a shrubland or heathland plant community found primarily in the U.S. state of California and in the northern portion of Lower California, Mexico. It is shaped by a Mediterranean climate (mild, wet winters and hot dry summers) and wildfire. Similar plant communities are found in the four other Mediterranean climate regions around the world, including the Mediterranean Basin (where it is known as maquis), central Chile (where it is called matorral), South African Cape Region (known there as fynbos), and in Western and Southern Australia.

The word chaparral is a loan word from Spanish. The Spanish word comes from the word chaparro, which means both small and dwarf evergreen oak, which itself comes from the Basque word txapar, with the same meaning.

A typical chaparral plant community consists of densely-growing evergreen scrub oaks and other drought-resistant shrubs. It often grows so densely that it is all but impenetrable to large animals and humans. This, and its generally arid condition, makes it notoriously prone to wildfires. Although many chaparral plant species require some fire cue (heat, smoke, or charred wood) for germination, chaparral plants are not "adapted" to fire per se. Rather, these species are adapted to particular fire regimes involving season, frequency, intensity and severity of the burn.

Ecology of fire in chaparral

Chaparral is one of the most fire-prone plant communities in North America because of thunderstorms. As a consequence, since an increasing number of developments are pushing into the backcountry along what is known as the wildland-urban interface, management of the system has become increasingly important.

There are two assumptions relating to California chaparral fire regimes that appear to have caused considerable confusion and controversy within the fields of wildfire and land management: first, older stands of chaparral become “senescent” or “decadent” implying they need fire to remain healthy (Hanes 1971), and second, fire suppression policies have allowed chaparral to accumulate unnatural levels of fuel leading to larger fires (Minnich 1983).

The perspective that older chaparral is unhealthy or unproductive may have originated during the 1940s when studies were conducted measuring the amount of forage available to deer populations in chaparral stands. However, according to recent studies, California chaparral is extraordinarily resilient to very long periods without fire (Keeley, Pfaff, and Safford 2005) and continues to maintain productive growth throughout pre-fire conditions (Hubbard 1986, Larigauderie et al. 1990). Seeds of many chaparral plants actually require 30 years or more worth of accumulated leaf litter before they will successfully germinate (e.g. scrub oak: Quercus berberidifolia, toyon: Heteromeles arbutifolia, holly-leafed cherry: Prunus ilicifolia). When intervals between fires drop below 10 to 15 years, many chaparral species are eliminated and the system is typically replaced by non-native, weedy grassland (Haidinger and Keeley 1993, Keeley 1995, Zedler 1995).

The idea that older chaparral is responsible for causing large fires was originally proposed in the 1980’s by comparing wildfires in Baja California and southern California. It was suggested that fire suppression activities in southern California allowed more fuel to accumulate which in turn led to larger fires (in Baja, fires often burn without active suppression efforts). This is similar to the argument that fire suppression in western United States has allowed Ponderosa Pine forests to become “overstocked.” In the past, surface-fires burned through these forests at intervals of anywhere between 4 and 36 years, clearing out the understory and creating a more ecologically balanced system. However, chaparral has a crown-fire regime, meaning fires consume the entire system whenever they burn. Detailed analysis of historical fire data has shown that fire suppression activities have failed to exclude fire from southern California chaparral as they have in Ponderosa Pine forests (Keeley et al. 1999). In addition, the number of fires is increasing in step with population growth. Overall, chaparral stand age does not have a significant correlation to its tendency to burn (Moritz et al. 2004). Low humidity, low fuel moisture, and high winds appear to be the primary factors in determining when a chaparral stand burns.

The Chaparral is a coastal biome with hot dry summers and mild, rainy winters. Droughts and fires are very normal during the summertime. The Chaparral area gets about 38 – 100 cm of precipitation a year and has an average temperature of 40ºC.

Species

In Central and Southern California chaparral forms a dominant habitat. Members of the chaparral biota native to California, all of which tend to regrow quickly after fires, include:

References

  • Haidinger, T.L., and J.E. Keeley. 1993. Role of high fire frequency in destruction of mixed chaparral. Madrono 40: 141-147.
  • Hanes, T. L. 1971. Succession after fire in the chaparral of southern California. Ecol. Monographs 41: 27-52.
  • Hubbard, R.F. 1986. Stand age and growth dynamics in chamise chaparral. Master’s thesis, San Diego State University, San Diego, California.
  • Keeley, J. E., C. J. Fotheringham, and M. Morais. 1999. Reexamining fire suppression impacts on brushland fire regimes. Science 284:1829-1832.
  • Keeley, J.E. 1995. Future of California floristics and systematics: wildfire threats to the California flora. Madrono 42: 175-179.
  • Keeley, J.E., A.H. Pfaff, and H.D. Stafford. 2005. Fire suppression impacts on postfire recovery of Sierra Nevada chaparral shrublands. International Journal of Wildland Fire 14: 255-265.
  • Larigauderie, A., T.W. Hubbard, and J. Kummerow. 1990. Growth dynamics of two chaparral shrub species with time after fire. Madrono 37: 225-236.
  • Minnich, R. A. 1983. Fire mosaics in southern California and northern Baja California. Science 219:1287-1294.
  • Moritz, M.A., J.E. Keeley, E.A. Johnson, and A.A. Schaffner. 2004. Testing a basic assumption of shrubland fire management: How important is fuel age? Frontiers in Ecology and the Environment 2:67-72.
  • Zedler, P.H. 1995. Fire frequency in southern California shrublands: biological effects and management options, pp. 101-112 in J.E. Keeley and T. Scott (eds.), Brushfires in California wildlands: ecology and resource management. International Association of Wildland Fire, Fairfield, Wash.
  • Campbell, Neil A.; Brad Williamson; Robin J. Heyden Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall.

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