Biological Sciences, Santa Barbara City College

Biology 100: Concepts of Biology

toyon and chamise off W. Camino Cielo.  S Williams photo

Hard Chaparral
Chaparral covers about 8.5% of California and is the most characteristic natural vegetative type in the state. It reaches its fullest development in Southern California where it ranges in elevation between 1,000 and 5,000. Annual grasslands and coastal sage scrub occur along its lower limits and its upper limits border on mixed evergreen and coniferous forests. Various types of woodlands bisect hard chaparral in foothill areas and along canyon bottoms.

Chaparral bisected by grassland. The chaparral in the foreground shows a variety of plant species. Soft chaparral is the gray color on the distant hills, hard chaparral the dark green color.

The evergreen, stiffly branched shrubs of the true, or hard chaparral are mostly 3 - 10 feet tall. Leaves are small and leathery (sclerophyllous) with thick cuticles. Sometimes the leaves are so reduced as to appear needle-like e.g. Chamise (Adenostoma fasciculatum). These are adaptations to reduce evapotranspiration during the dry summer months. Stands of mature chaparral form a dense, almost impenetrable layer with little or no herbaceous understory.

Hard chaparral occurs in a mosaic reflecting fire history. A twenty year cycle of fire maintains a community of Chamise. In communities with less frequent or more regular burns Chamise gives way to Ceanothus, mountain mahogany, Sumac, Toyon and Manzanita . Dwarfed oaks and drought-resistant, closed-cone pines also occur.

Many of the chaparral plant taxa display adaptations to fire. These include

  • the flammable oils of chamise and other shrub species promote fire.
  • chamise, manzanita and scrub oak resprout from basal burls after a burn.
  • the resin coating of cones of closed-cone pines melts in a hot fire and allows the cones to open and disperse their seeds.
  • perennial forbs survive as underground bulbs and sprout quickly in response to the addition of nutrients to the soil after a burn.
  • the rosette shape of yuccas protects the inner growth bud from destruction in all but the hottest fires.
  • scorching increases germination in Big Pod Ceanothus, manzanita and fire poppies.

Adaptations to drought

Rain generally falls over the winter months in a few intense storms. The effective moisture is drastically reduced by rapid runoff, low moisture retention by soils, high rates of evaporation and the protracted rainless period each year. To survive, chaparral plants must be adapted to 5 - 6 inches of rain per year and a drought of 5 - 6 months in duration. The dominant species are mostly spring active - they photosynthesize and grow in the spring when after moisture from the winter rains has penetrated far enough into the soil to become available to their roots.  As soil moisture supplies become limited, usually by late June, most chaparral plants enter a summer dormancy phase and operate at 5% of their wet season maximums. The plants are most susceptible to fire at this time.

By retaining their leaves, plants of the hard chaparral are physiologically ready to take advantage of a rare summer thundershower. Within minutes of the moisture being absorbed by the roots, the plants will be photosynthesizing. Their evergreenness makes them opportunists who can use soil moisture as soon as it becomes available. The leaves of the evergreen sclerophyll do not wilt so no part of the new water supply need be spent in rehydrating the leaves to maximize light absorption.

Adaptations Function
Small leaves

Less surface area from which water can be lost.
Thick leaves Prevent leaves from "overheating". This insulation keeps leaves at a cooler temperature, slowing transpiration.
Waxy coating

Serves as a barrier to water loss.
Gray green reflecting (dark tops, light undersides) Reflect light and heat from leaf surface, reduce loss of water.
Recessed stomata on undersurface of leaf Stomata are the pores in leaves permitting evaporation and the exchange of oxygen and carbon dioxide
Vertical orientation of leaves

Decrease in absorption of sunlight by leaves. This helps to keep the leaves cool
Hairs on leaves

Trap water vapor and slow down the rate of water loss.
Drought adaptation table from

Succession and Aging

For the chaparral community, disturbance = diversity. It rapidly recovers from disturbance by fire, erosion or man. Chaparral succession is unique in that it succeeds itself rather than being preceded by other vegetative types.  However, grasslands will become the dominant community if the previously chaparral-covered area burns many times within a short time period.  This reduces the chance of regrowth from burls or from seeds germinating, growing to maturity and casting their own seeds.  Tje area is also more prone to invasion from non-native colonizing species. 

When a chaparral area is prevented from undergoing burns (because of its proximity to a city for example) the accumulated biomass is so great that when the fire eventually occurs it is hot enough to destroy the underground plant structures that would otherwise guarantee the chaparral's succession by more chaparral.  These underground plant structures include buds on woody tap roots (lignotubers), burls, and underground rhizomes.  However the seeds of the chaparral shrubs remain viable after high intensity burns and the area will eventually again become a stand of mature chaparral.

Immediately after a disturbance the herbs and forbs initially dominate because of their sheer numbers and showy flowers. Within 2 - 5 years the seedlings of chaparral plants and the shrubs resprouting from their crown roots or burls take over. Their more aggressive root systems exploit deeper water reserves and they will eventually shade out the forbs and grasses and replace them.

Productive growth is maintained in the canopy in mature unburned stands of chaparral. Common plants such as scrub oak, toyon, and holly leaf cherry all require a leaf litter that is at least 30 years old before they will germinate successfully.  When the fire interval is short, for example between 10 - 15 years, these shrubs may be eliminated and the whole chaparral system replaced by grassland.  Plant growth does not occur under the chaparral canopy due to lack of light, activity of herbivores and the fact that the seeds contained in the ground covering leaf litter are dormant.

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