Postfire Succession of the Herbaceous Flora in Southern California Chaparral

Postfire succesion of the temporary herbaceous and suffrutescent cover was studied after chaparral fires in San Diego County, California, USA. Four categories of species make up the temporary cover. (1) "Generalized herbaceous perennials" are present before and after fire. Populations of these herbs are sparse under the shrub canopy. They resprout after fire from bulbs or other underground parts and postfire populations are sparse. (2) "Generalized annuals" are present in openings before fire but produce their peak population size in the first few years after fire. (3) Specialized "fire—annuals" are more or less restricted to the 1st postfire yr. (4) Specialized "fire—perennials" (subshrubs) are uncommon before fire, establish from seed in the 1st postfire yr and reach maximum cover in the 3rd and 4th yr. Community—level changes in cover and diversity are interpreted in light of differences in population dynamics of the four groups. Specis richness was highest in the 1st yr after fire because this was the only time all four groups were present together. Throughout succession herbaceous species richness was positively related to herb cover, negatively related to elevation and unrelated to slope aspect. The number of annual species fluctuated greatly through succession at all sites, but the number of herbaceous perennials did not. Herb cover fluctuated markedly from year to year and was positively related to amount of annual precipitation and negatively related to subshrub or "fire—perennial" cover. Artificial seeding with annual rye grass Lolium multiflorum had not apparent effect on total herb cover since sites with poor Lolium establishment had as high or higher herb cover as sites with high Lolium establishment. Lolium success was at the expense of the native cover and this negative effect was greatest on the "fire annuals."