Published online by Cambridge University Press: 05 December 2011
The evolutionary significance of natural fire disturbance regimes in the development of post-fire fungal and herb communities is examined. Before a fire the soil microflora exhibits a general fungistasis, microbial competition is great, nutrients are limiting, and carbonicolous ascomycetes are in a dormant phase. Also in mature chaparral shrub communities the soil microflora is implicated in soil toxicity that prevents seeds of some species from germinating in the interval between burns. Fire results in the deposition of ash and charred wood, a release of nutrients, the elimination of competitors (e.g. shrub cover, soil microflora), an increase in soil alkalinity, the removal of soil toxicity/fungistasis, and cues the germination of constitutively dormant ascospores and seeds. The cue for germination of the chaparral fire annuals appears to be components of the hemicellulose fraction, produced during the charring of wood, but this fraction has not been tested for its ability to cue ascospore germination. Germination in the absence of fire would be “suicidal” because neither the carbonicolous ascomycetes nor the post-fire annuals are able to compete successfully in these pre-burn habitats. The frequency of burning and the uneven heating of the soil surface creates patchiness with a corresponding increase in the species richness of the post-burn community.