Ecology of Vertebrate Animals in Relation to Chaparral Fire in the Sierra Nevada Foothills

Chaparral fire brings decided changes in the species composition and density of both plant and animal populations in the Sierra Nevada foothills. Some species decrease whereas others increase following a burn, but not species is totally eliminated, nor is there any apparent diminution of total life on a burn after plant growth resumes. These conclusions were reached in the course of a 4—year study of adjoining burnedand unburned areas near Glennville, Kern County, California. Field work began in 1953 at which time study plots were selected and plant and vertebrate population were censused. A year later part of the study area was burned, and ensuing investigation compared populations on the burned and check areas for a period of 3 years, terminating in 1957. At the time of the fire, temperatures were recorded in sites both above and below ground, and the actions of animals were observed. There was very little evidence of direct mortality among any of the vertebrates, most of them escaping the heat in one way or another. The woodrat was perhaps the most vulnerable species because of its dependence on houses made of dry twigs. However, in the bare ash after the fire many species were severely exposed to predation, and populations of the most small mammals and some brush—dwelling birds decreased rapidly. Predatory birds and mammals increased, as did some seed—eating birds that found good foraging on the exposed earth. When the rains stimulated new plant growth, a very different habitat developed in the area of burned chaparral. Most of the original trees sustained little damage, although the pitchy digger pines were largely eliminated. However, the extensive brush stands were reduced by almost 90%, and there was a corresponding increase in invading grasses and forbs. Birds and mammals that normally exhibit a strong preference for chaparral habitat were substantially reduced in numbers in the years following the burn. Conversely, some of the birds that normally prefer grassland or oak woodland increased in number. The fire resulted in an overall increase in densities of nesting birds. None of the small mammals increased in numbers but some of the larger predators, such as the coyote and badger, moved into the burn during the months following the fire.