POPULATION BIOLOGY OF BONAMIA GRANDIFLORA (CONVOLVULACEAE): EFFECTS OF FIRE ON PLANT AND SEED BANK DYNAMICS

The effects of disturbance on reproduction and plant and seed bank dynamics in the perennial herb Bonamia grandiflora were studied by comparing populations in recently burned, mechanically disturbed, and undisturbed habitats in central Florida over a 3‐year period. Plant densities, seed production, and the occurrence of herbivory and predispersal seed predation varied considerably between sites and between years, with recently disturbed sites supporting the densest and most dynamic populations. Death of established plants was rare in all sites. In each site, the soil seed bank was several‐fold larger than single season seed rains suggesting that B. grandiflora seeds are long‐lived and accumulate in the soil. There was no evidence that postdispersal predation or pathogens have any significant influence on the seed bank dynamics. Fire resulted in large increases in stem densities due to both increased clonal stem production and new genet recruitment from seed. Burning also caused significant increases in the percentage of flowers producing seed and the numbers of capsules and seeds per plant. The seed rain was ten to thirty times greater in the burned site relative to adjacent unburned site during the 3 years after burning. However, additions to the seed bank from the postfire seed rain were balanced by equivalent losses due primarily to seed mortality during fire, and to a much lesser extent due to germination and new genet establishment. As a result, the subsequent densities of seeds stored in the soil in these two sites were similar, indicating that fire results in a significant turnover in the seed bank population but no immediate change in its size. These effects on seed bank dynamics, in addition to new genet recruitment, suggest that periodic fires may play an important role in the maintenance of genetic variability as well as the size of these populations.