Size Structure and Seed Production in Even-Aged Populations of Ceanothus Greggii in Mixed Chaparral

The obligate-seeding chaparral shrub Ceanothus greggii is killed by fire and so depends entirely on seeds for persistence. We report on a 5-year study of changes in population structure and seed production from even-aged cohorts in matched north and south-facing mixed chaparral last bumed 6 (1977), 13 (1970), 32 (1951), 57 (1926) and 82 (1901) years before 1983. The density and proportion of live C. greggii shrubs declined significantly over the age sequence. We estimate that C. greggii shrubs will die out locally in chaparral unburned for 85-155 years. Analysis of changes in skewness in size distributions among even-aged cohorts did not reveal a consistent increase followed by a decrease with age, as predicted by theory (...)