Reproduction of Chaparral Shrubs After Fire: A Comparison of Sprouting and Seeding Strategies

Abstract

The relative ability of sprouting and nonsprouting chaparral shrubs to recover from fire was studied by examining popula- tion of congeneric pairs of species in burned and adjacent unburned areas. The pairs of species selected, with the nonsprouting species named first, were Arctostaphylos glauca ? A. glandulosa and Ceanothus greg- gll - C. leucodermls. Data were also obtained on certain associated species, particularly Adenostoma fasclculatum. The numbers, sizes and condition of the component species at each of the sites were measured. Both sprouting and nonsprouting species showed vigorous recovery from fire. It seemed likely that the burned stands would eventually reach a state of development comparable to that shown in the preburn stand without any significant shifts in composition Mortality of shrubs resulting from the fire was complete for nonsprouters but varied in sprouting species. In some there was essentially no mortality, while in others, especially Adenostoma, it was rather high. Seedling establish- ment in the shrub species varied markedly and seemed to be correlated with the degree of fire-caused mortality. A profound difference was observed in the life histories of the two nonsprouting shrubs. Whereas Ceanothus greggll produced a very high number of seedlings after fire, Arctostaphylos glauca produced substan- tially fewer. A comparison of the density-size distribution of live and dead stems indicated that C. greggll suffers high mortality early in suc- cession, but A. glauca loses very few individuals even after 90 years without fire. In light of these results a model is proposed which we be- lieve explains the adaptive significance of the obligate-seeding strategy in the southern California chaparral.