Description

The combination of improper land use and attempts at total fire exclusion from the wildlands of Southern California have caused major changes in the vegetation. These changes are continuing, especially in the forested areas which have suffered severed losses recently and may be expected to suffer further losses in the near future from high-intensity wildfires. Where early Spanish diaries recorded open grasslands with a few scattered pockets of chaparral on steep, shallow soils, there are now vast areas of dense brush. Heavy overgrazing by indtroduced livestock reduced the competition from lthe native grasses and permitted the establishment and spread of brush seedlings. The overgrazing also removed fine herbaceous fuels that previously carried low-intensity fires. The fire-sensitive shrubs were aided in their spread by the elimination or reduction of frequent, low-intensity fires. The interval between possible successive fires lengthened to twenty years or more; the time necessary for the shrubs to accumulate enough dead material to carry fire. The longer interval between fires created higher-intensity fires because of the greater biomass and made conditions mor favorable for the fire adaptations of the chaparral species. Fire protection policies of the past 65 years have allowed similar invasions of brush species into the oak woodlands and coniferous forests. The frequent, low-intensity fires that killed young brush seedlings and prevented accumulations of large quantities of dead fuels have been eliminated. Instead, there are now infrequent, high-intensity wildfires that kill nearly all the trees. Large conifers that survived centruies of uncontrolled fires are being destroyed through the impact of modern fire control policies.