Reproduction and growth of the chaparral geophyte, Zigadenus fremontii (Liliaceae), in relation to fire

Abstract

Zigadenusfremontii is often a striking component of the flora following firein the chaparral. Like other geophytes, it produces large numbers of flowers inthe first spring after a burn. Although these plants are most conspicuous intheearly postfire environment, the question that remains is, how do they persistinthe interval between fires? To address this we investigated differences in thegrowth and reproduction of Z. fremontii in burned andunburned chaparral. We monitored marked individuals for nine years at threesites: two that were burned in 1990 and one in the same area that was inunburned mature chaparral. We measured leaf area, and production of flowers andfruits. We also conducted seed experiments in the field to determine the ratesand timing of germination. We found that reproduction occurs only in theimmediate postfireperiod: flowering and production of fruits and seeds in the first yearfollowingfire, and seedling establishment by year 3. There was a cost of reproduction;plants that flowered (in the burn area) had negative growth rates the followingyear. In contrast, plants in unburned chaparral, which did not flower, hadpositive growth rates over the same period. Moreover, plants that produced themost flowers had the lowest growth rates. In the unburned chaparral site,plantswere not dormant as predicted from previous literature; instead they producedleaves nearly every year. In most years the average leaf area per plant wasgreater than that in the burned sites. Our results indicate that postfirereproduction depends on growth and carbohydrate storage in the inter-fireperiod. We also suggest that this species is relatively long-lived for aherbaceous perennial.