Ceanothus left; Manzanita right
CHAPARRAL: CALIFORNIA AND SOUTHWESTERN U.S.
Chaparral is a general term that applies to various types of brushland found in southern California and the southwestern U.S. Plants such as manzanita, ceanothus, chamise and scrub oak, along with other grasses and forbs, are examples of typical chaparral flora. This community contains the most flammable type of vegetation found in the United States. It is no surprise, then, that many of these species are well-adapted to fire and some actually possess traits that encourage fire.
One chaparral plant, Ceanothus, has leaves that are coated with flammable .Resins. Ceanothus seeds require intense heat for germination, and its roots are specially adapted to enable the plant to grow in areas that were recently burned. Other chaparral shrubs also contain flammable oils and resins in their leaves. The leaves and branches of these plants are small, adding to their flammability.
Chaparral plants sprout quickly, and grow and spread rapidly. This rapid growth, along with the plants' ability to produce heat-resistant seeds that remain dormant yet viable in ground litter for long periods of time, contributes to the ability of chaparral flora to recover quickly following fire. Furthermore, many nutrients are locked in the foliage of chaparral plants. Through burning, these nutrients are recycled back into the soil.
With age, chaparral plants become less productive but are not overtaken by invading species. Fire in this type of community serves to replace older plants with younger, more productive ones of the same species rather than to eliminate exotic species and replace them with native ones, as is the case in tall grass prairies.
Second source states: from:http://www.rain.org/~riveray/html/Files_Indexes/natural_history.files/chaparral/chap_country.html
"Just overhead is the chaparral, a sterile environment by comparison to that found in the canyons. Because it is dry, dull, and difficult to pass through, the chaparral is difficult to appreciate. The key element in the chaparral life cycle is fire, and nature has predated this scrubby brush to respond to the slightest spark. It is not uncommon for fuel moistures to drop to 8 to 13 percent during summer drought periods or during Santa Ana conditions. In addition, the close spacing and continuity of the cover and the high surface-to-volume ratios in the chaparral community leads to a high percentage of available fuel.
Over time, the ratio of dead fuel to live plant material increases dramatically. For example, by age 30 often as much as 50 percent of the standing mass of the chaparral is dead, and dry material litters the ground. Where such conditions exist over large mountainous expanses, fires, when ignited, tend to be quite large.
Though the chaparral seems tough on the surface, it is actually a very delicately balanced community, well adapted to water stress. Over many millions of years, the chaparral has evolved an equilibrium between water conservation and water use. One of the adaptive features is the solid continuity of the brush cover and its nearly uniform height, which helps minimize evaporation and retain winter moisture through the long summer months of water deprivation. Holding fast to this soil moisture in the summertime is critical, and the even mantle acts like a blanket that protects the soil from wind and solar radiation.
While the cover tends to minimize soil moisture loss, the leaf structure of the chaparral plants is sclerophylous, which means it is well adapted to resist water loss. Some plants, like scrub oak or holly-leaf cherry, have a heavy wax cuticle on the leaves and stems, which helps reduce water loss. On other plants, dense mats of hairs serve the same function. Another adaptation is vertical orientation of leaves, or, as in the case of sugar bush, the leaves are curled so that they do not receive sunlight directly. The greyish color of plants like white or purple sage or yerba santa also reduces the heating up of the plant tissues. Further, sunken stomata on the leaves of these plants help make water loss mimimal.
Most of the leaves of the chaparral plants are also desiccation-tolerant, which means that the leaf structure resists damage during long dry periods. Nevertheless there are limits to the length of time these plants can survive water stress and many are drought deciduous as well. Often, after 100 days or more of prolonged drought, many begin to lose their leaves, bringing evaporation loss almost to a halt. Plants that drop their leaves commonly develop smaller leaves on side shoots of the main stems, and it is these tiny leaves that enable them to persist through extended drought.
Most chaparral plants produce chemicals that inhibit other plants from invading their territory. Through a process called allelopathy, the chemicals invade the soil from the leaf litter and prevent roots of other plants from competing for the soil moisture. These toxins are so potent that in some cases, as with the bush poppy or certain species of ceanothus, the spaces that they occupy may remain open and uninvaded 20 to 40 years after they have been killed off by wildfire.
The main adaptation of the chaparral to its arid conditions, however, is its response to fire, which initiates a new cycle of plant succession. In the hard chaparral the buildup of dead plant material tends to ensure the continuity of fire, while in the softer chaparral it is the volatile and highly flammable oils that do so. After a fire, annuals and short-lived perennials, called fire followers, temporarily dominate the hillsides, producing spectacular displays of wildflowers. In about two to five years after a fire though, almost all of these species stop growing and their spaces are usually taken by the expanding canopies of the resprouting or regrowing chaparral shrubs. The seeds of these herbaceous fire followers persist in the soil until released by heat from the next wildfire.
Once a shrub occupies the space held by the fire followers, it physically dominates that site, primarily because of its allelopathy. Not until the next fire will the cycle begin anew. Viewed on a linear scale, the chaparral life cycle can be seen as a series of "pulses", each initiated by fire. Removal of the older brush by intense wildfires that occasionally sweep across the mountain wall is not just an adversity that these plants must overcome, but a necessary part of their life cycle. Unlike some other ecosystems, which require many years to redevelop a healthy diversity once fire has disturbed them, the chaparral is actually healthiest and contains the widest variety of plant and animal species in the years immediately after fire. The concern is not so much if chaparral will recover after fire, or how long it will take, but rather how rapidly the ecosystem will decline if fire is withheld.
Woven through the almost impenetrable tangle are the trails of smaller animals, though without fire, the wildlife does not fare well. As the fuel volume of the chaparral increases, its food productivity decreases. Wildfire prunes out the dead wood, causes rapid regrowth, and permits the spread of annuals and herbs, which are retarded by the thick overstory. Generally, fire favors wildlife by resetting the botanical time clock back a notch to earlier periods of plant succession, thus forcing the vegetation to produce more food.
Almost anywhere off-trail you can see the effect of this fire ecology directly. The branches of the stiff-twigged shrubs make passage within this habitat difficult. Except for the recent Painted Cave Fire, these mountains have not burned in the past two decades, and except for the outer edges of the bushes, most of the limbs are dead. The chaparral plants grow only at their tips."
