Factors Contributing to Postfire Seedling Establishment in Chaparral: Direct and Indirect Effects of Fire

Abstract

1 In the chaparral significant seedling establishment occurs only following fire. Mechanisms proposed to explain this abundant recruitment after fire include: direct heating of the soil and seed bank, and a temporary reduction in competition or herbivory. 2 I tested hypotheses regarding the relative importance of these mechanisms to different plant functional groups using field experiments conducted in burned and nearby unburned chaparral. Competition was manipulated by removing shrubs from mature chaparral, and mammalian herbivory manipulated using small cage exclosures. 3 Burning and reduction in herbivory were primarily responsible for the postburn 'flush' of seedlings, although plant functional groups differed in their responses to fire. 4 Shrub seedling density was enhanced only by herbivore exclusion. The abundance of subshrubs and annual herbs was positively affected only by burning. Perennial herbs increased both with burning and herbivore exclusion. 5 The effects of variation in fire intensity or soil heating were also investigated, by comparing unmanipulated plots in the burn to areas in the burn which had been cleared of shrubs prior to the fire. 6 Areas in the burn with reduced soil heating had higher overall seedling densities, cover and biomass; perennial herbs were the only functional group unaffected by variation in fire intensity. 7 Comparison of the results of this study to those from similar experiments in maritime chaparral suggest that inconsistencies between the responses of chaparral communities to fire may be due primarily to differences in species composition.