Role of Fire in Seed Germination of Woody Taxa in California Chaparral

Abstract

Germination behavior of 45 tree, shrub, subshrub, and liana taxa from fireprone coastal sage scrub and chaparral was investigated. Seeds were sown on filter paper or potting soil, in the light or dark, with or without powdered charred wood (charate), and after heating treatments of 1 h at 70°, 5 min at 100°, 5 min at 120°C, or no heat. Germination medium had a significant effect on >70% of the species, although the pattern of response to other treatments remained the same on both media. Germination of over half of the species was inhibited in the dark, but two species were light inhibited. Charate significantly enhanced the germination of approximately a quarter of the species. A similar proportion of species exhibited heat—stimulated germination. In only a few species did both heat and charate play a role in stimulating germination. Nearly a third of the species had seeds that germinated readily upon wetting, and germination was not further stimulated by any fire—related cue. These different germination syndromes are correlated with different life history syndromes. Most coastal sage subshrubs germinate readily in the absence of fire—related stimuli and thus are capable of colonizing other forms of disturbance. For many of these species, germination was inhibited in the dark. This may result in a portion of the seed pool remaining dormant until fire since, in the case of several species, dark inhibition is overcome by charate. Chaparral shrubs and trees that germinate readily upon wetting seldom establish seedlings after fire. Their persistance in these fire—prone environments is due to resprouting after fire. Seedling establishment and population expansion for such species is dependent upon extended fire—free periods. In contrast, woody species that fail to germinate without some fire—related cue have seedling establishment and potential population expansion restricted to postfire conditions. The present mixture in species composition may be maintained by variable burning regimes.