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

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Abstract
The relative ability of sprouting and nonsprouting chaparral shrubs to recover from fire was studied by examining population of congeneric pairs of species in burned and adjacent unburned areas. The pairs of species selected, with the nonsprouting species named 1st, were Arctostaphylos glauca - A. glandulosa and Ceanothus greggii - C. leucodermis. Data were also obtained on certain associated species, particularly Adenostoma fasciculatum. The numbers, sizes and conditions of the component species at each of the sites were measured. Both sprouting and nonsprouting species showed vigorous recovery from fire. The burned stands would eventually reach a state of development comparable to that shown in the preburn stand without any significant shifts in composiition. 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 other, especially Adenostoma, it was rather high. Seedling establishment 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 2 nonsprouting shrubs. Whereas C. greggii produced a high number of seedlings after fire, A. glauca produced fewer. A comparison of the density-size distribution of live and dead stems indicated that C. greggii suffers high mortality early in succession, but A. glauca loses few individuals even after 90 yr without fire. In light of these results a model is proposed which explains the adaptive significance of the obligate-seeding strategy in the southern California [USA] chaparral.