Chaparral Community

Chaparral communities are dominated by evergreen, stiffly branched, needle or broad leathery-leafed (sclerophyllous) shrubs mostly 3 to 10 feet tall.  True chaparral is often referred to as "hard chaparral" because of these features, whereas coastal scrub is often referred to as "soft chaparral".  Chaparral communities are normally extremely dense and form an almost impenetrable shrubby communities with little understory.  Some stands are composed of more open stands of shrubs that sometimes gain the stature of small, bushy trees. Chaparral is a quite variable and is often composed of a diverisity of different species.  As a result, chaparral communities have been subdivided into several different types depending on location and dominant species. Chaparral is the characteristic plant cover on steep slopes that are too hot and dry to support coastal live oak woodland.  The soils of chaparral are generally shallow, infertile, rocky or gravelly in texture and have a low water holding capacity.  Chaparral soils are also highly erodible.

Chaparral communities cover approximately 10% of California and occur in scattered locations in the foothills of the mountains in both northern and southern California.  In southern California, chaparral communities are a dominant feature of the landscape where they cover much of the lower elevation of the southern California mountains and are also found in the areas of lower elevation near the coast.  In the coastal regions of the central and southern california, chaparral communities are closely associated to coastal scrub communities.  Chaparral communities are often subject to large seasonal temperature fluctuations with high summer temperatures and low winter temperatures.

Soils encountered in chaparral communities are often shallow, rocky, and nutrient poor.  However, chaparral communities do occur on a variety of substrates ranging from stablized sand dunes along the ocean (such as in Montana de Oro State Park near Morro Bay) to serpentine soils (such as in Poly Canyon and on Cuesta Grade).

Herbaceous undergrowth is usually very sparse or nonexistent in mature chaparral stands due to several factors.  Chaparral shrubs have been found to have chemical compounds that are leached out of the litter or canopy foilage and accumulate in the soil below that inhibit herbaceous plant growth (allelopathy).  Some compounds may also be volatilized into the air by warm temperatures.  Another factor inhibiting herbaceous gowth may be foraging herbivores that eat the seeds and seedlings under and near the shrubs.  These are usually small birds and mammals that use the shrub canopy as protection from predators such as hawks.   They often venture out just a short distance from the protection of the canopy to forage.  As a result, they eat the seeds the blow into the chaparral as well as those immediately around the margin of the canopy.  This is one factor that contributes to the characteristic bare zone that often occurs along the margins of chaparral and coastal scrub communities.

Chaparral communities are very closely associated with fire.  Chaparral shrubs are very flammable due to the resinous foliage, woody stems, accumulated litter, and standing dead branches.  Wildfires play a key ecological role in the development and perpetuation of these communities.  Chaparral shrubs are highly adapted to fire by either re-sprouting from an underground burl (lignotuber) or by having seeds that are stimulated to germinate by the heat treatment of the fire and by chemicals in the charcoal left after the fire.

Dominant chaparral species have various adaptations to fire.  Plants such as Adenostoma fasciculatum (chamise), Lonicera interrupta (chaparral honeysuckle), and species of Arctostaphylos (manzanita) have thick, woody underground structures (root-crowns, lignotubers, and basal burls) that are protected from the extreme heat of the fire by the soil's insulating properties.  These readily re-sprout following fires and regenerate the shrubs quickly after the fire.  Other plants may have extensive underground rhizome systems such as Toxicodendron diversilobum (poison oak) that also re-sprout following fire.  In addition, some plants have seeds protected under the soil surface that germinate readily as a result of heat scarcification or released chemicals from the burnt stems.  Often profuse seed germination follows a chaparral fire, and herbaceous plants competely carpet the ground until the shrubs grow and again attain dominance.  Once shrubs are again the dominants, the combination of competition, allelopathy created by the shrubs, and the return of the small, foraging animals under the shrub canopy reduce the herbaceous cover.

Some herbaceous species only germinate following a fire.  These "fire annuals",  "fire followers", or "pyrophyte endemics" have seeds that are retained in the soil for 50 years or longer following a fire and only germinate after a fire.  Papaver californicum (fire poppy) is an example.  Fire poppies germinate profusely immediately following a fire and may remain on the burn site for several years but eventually disappear as the chaparral species return.  However, the seeds of the fire poppy, like other fire annuals, will remain viable for many years and will regerminate again when the next fire comes through the area.  

Chaparral communities are very diverse and vary  signicificantly in species composition from place to place.  Close to 900 species of vascular plants occur in chaparral and about 240 of these are woody plants (mostly shrubs). Many different types of chaparral communities are found in California depending on local environmental conditions.  Chaparral communities are not only found on the dry, hot, rocky slopes of the foothills but also occur at higher elevations (montane chaparral) and in some semi-desert regions (desert chaparral).  While coastal scrub (soft chaparral) is common in Poly Canyon, true or hard chaparral is not.  It does occur in small patches but it is not well developed.  However, on Cuesta Ridge above Poly Canyon, chaparral communities are often the dominant cover on the steep, rocky slopes and ridgetops.

For further information on chaparral series and communities please consult the book written by V.L.Holland and David J. Keil California Vegetation.

Some of the common chaparral species that occur in Poly Canyon are listed below.

Adenostoma fasciculatum (Chamise)
Cercocarpus betuloides (mountain mahogany)
Fremontodendron californicum (flannelbush)
Heteromeles arbutifolia (toyon)
Lotus scoparius (deerweed)
Prunus ilicifolia (holly-leafed cherry)
Rhamnus californica (coffeeberry)
Rhamnus crocea (redberry)
Salvia mellifera (black sage)
Toxicodendron diversilobum (poison-oak)