Recent Fire History of Maritime Chaparral Dominated by Arctostaphylos morroensis

Dennis Odion and Claudia Tyler

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Published: October 30, 2003

We agree with Ward (2003) that time scales spanning far more than one fire cycle are needed to understand the ecological and evolutionary effects of fire. Time scales of this type underlie the reproductive ecology of Morro manzanita, including such factors as rates of seed accumulation.

Ward observes that our paper did not include a complete fire history of the study site and suggested that there were probably frequent fires prior to 1958 because the area was used by the U.S. Army as a firing range. We welcome the opportunity to provide more information about the history of the site. We did study aerial photographs to determine if fires had occurred prior to 1958. The earliest photographs available were taken in 1949, and we found no evidence of burning in photos dating from 1949 to 1958. In addition, based on our experience identifying past burns in maritime chaparral using air photos (e.g., Davis et al.1988), we feel confident that we would have detected evidence of fires that occurred up to 10–15 or more years prior to 1949. Our photo analysis is described in a report to the California Department of Fish and Game (Tyler and Odion 1996). In addition to climate/weather factors, the fragmented nature of patches of chaparral in the study area may contribute to the low present and past probability of burning. Finally, we have no evidence that the study area was used as a bombing range. The information provided to us by park personnel, who were aware that we would be digging up soil samples, was that the ordnance at the site was unexploded bullet ammunition. In summary, we have no evidence to support the idea that fire was common in the decades prior to the establishment of the even-aged stand we studied.

In addition, the possible occurrence of fires prior to 1958 does not contradict our conclusion that the seed bank in a 40-yr-old stand was not sufficient to compensate for mortality and maintain population sizes of Arctostaphylos morroensis through a burn, and that this species may require considerably longer than 40 yr to establish a seed bank that is adequate to prevent population decline or local extinction. We hypothesized that this prolonged "immaturity risk" may be explained by specialization of this species to a historic regime of relatively infrequent fire. We welcome alternative hypotheses to explain the persistence of this and other maritime chaparral species, given our evidence that many decades are required for adequate seed accumulation.

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Davis, F. W., D. E. Hickson, and D. C. Odion. 1988. Vegetation composition in relation to age since burning and soil factors in maritime chaparral, California. Madroño 35: 169-195.

Tyler, C. M., and D. C. Odion. 1996. Ecological studies of Morro manzanita (Arctostaphylos morroensis). California Department of Fish and Game, Sacramento, California, USA.

Ward, D. J. 2003. Fire history of Montana de Oro State Park. Conservation Ecology 7(1): r7. [online] URL: http://www.consecol.org/vol7/iss1/resp7.