Biological Sciences, Santa Barbara City College

Biology 100: Concepts of Biology



In addition to Southern California, chaparral communities are found in Europe around the Mediterranean, in the African Cape region, central Chile and southwestern Australia.  The word chaparral comes from the Spanish "chaparro", a dense growth of shrubby evergreen oaks or low-growing vegetation.  The chaparral of Southern California consists of two plant associations. These are the coastal scrub community, or soft chaparral, and the true, or hard, chaparral of the foothills. In Southern California, the chaparral communities are the dominant features of the landscape. They cover much of the lower elevations of the local mountains and low lying coastal areas.
General Characteristics of the Chaparral communities

Climate

Southern California is in a Mediterranean climatic region. This region occurs between 30 and 40 degrees of latitude on the west coasts of continents with cold ocean currents offshore. These regions have cool, wet winter seasons with limited rainfall generally occurring in a few intense storms. Summers are hot, dry and accompanied by drought. The coastal areas experience more moderate climates than the interior due to the marine influence and the fogs associated with the cold ocean currents. During the summer months fog may even provide some moisture to the plants within the fog belt. There is a limited, but predictable, growing season during the winter and spring when there are both sufficient soil moisture and warm temperatures. Temperature and water stresses occur during the hot, dry summer months. Local conditions of soil and slope may greatly modify regional climates.

Southern California contains distinctive types of woody plant communities. Included are evergreen forests and woodlands, evergreen scrubs (hard chaparral), and drought-deciduous scrubs (coastal sage or soft chaparral).


Absence of an herbaceous understory

Allelopathy
Both the hard and soft chaparral plant communities lack a defined ground cover layer. This is caused by chemical inhibitors called allelopathic agents. These volatile or water-soluble chemicals are exuded by the chaparral shrubs and carried by the heat of the day or by water to the soil. The allelopathic agents may also leach out of the leaves or leaf litter to accumulate in the soil beneath. These compounds effectively stunt the growth of plants and reduce or eliminate seed germination. Allelopathy is a plant defensive mechanism. It ensures the limited moisture and nutrients available in the soil are only capable of being used by the plant producing the allelopathic chemicals.

Allelopathy in white sage

Foraging herbivores
Foraging herbivores may eat the seeds and seedlings under or near the shrubs. These small birds and mammals use the dense shrub layer as protection from hawks and other predators. These herbivores only venture a short distance out from the margin of the chaparral. This is one factor that contributes to the characteristic bare zone around the edges of chaparral and coastal sage communities.

Geographical considerations
The overriding geographical factors that influence chaparral development are slope aspect, elevation, soil type and fire.

Slope angle and aspect

The position on a slope relative to north is called slope aspect. Slope aspect is the most important selective factor in the chaparral environment. It influences which species make up the local chaparral community as well as the changes and rates of change within the community following fire or other disturbances. Most chaparral in southern California grows on geologically young mountains where steep slopes are in the 25 - 70 range.

Slope and exposure are critical with different plants found on the moist northern exposures and dry southern exposures. On south-facing slopes mixed stands of chaparral become less diverse over time and tend to become dominated by chamise. On north facing slopes, although the die-off process is evident, chaparral stands remain rich in species diversity.

Hurricane Deck.  S Williams photo
Foreground slope shows a variety of species. The solid dark green of the background shows no diversity. These slopes are covered with chamise.

Soils
Soil develops through physical and chemical weathering of a thin surface layer of rock and mineral fragments. Soil texture and structure determine what kind of plant life a soil can support. Chaparral soils are generally shallow and infertile over a highly fractured bedrock.

Copyright 2002  
Return to previous page
 Go Back  Top