Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

William J. Platt

Abstract

The effects of three fire seasons (May, August, and January) on reproductive success and clonal growth of a golden aster (Pityopsis graminifolia) were examined within experimental burn plots in a longleaf pine savanna in north Florida. Several factors influenced reproductive success in this species, including rates of floral induction and bud herbivory, clone fecundity, and seedling dynamics. Flowering was induced by fire, especially when it occurred in May or August. Fire season affected rates of floral induction and bud herbivory by as much as one to two orders of magnitude. Sizes of bolting shoots were also affected by fire season. Survival of 1991 cohorts of seedlings through December 1992 was highest in May-burned plots, intermediate in August-burned plots, and lowest in January-burned plots. Fire season also influenced patterns of clonal growth in this species. May fires caused higher short-term per shoot rates of increase in shoot density than did either January or August fires. May fires also resulted in greater numbers of shoots/clone than did either January or August fires. January-burned plots contained clones with larger (but fewer) shoots than did May-burned or August-burned plots. Such variation in clone structure may indicate a greater capacity of clones to locate soil resources following May fires than following January or August fires. The reproductive and clonal responses of this species to fire season indicate that plants perform best following fires in May, the season in which lightning fires are most likely to occur. Models of resource allocation and clonal growth dynamics revealed that widespread but short-lived increases in rates of vegetative spread following May fires corresponded to a hypothesized shift in competition from aboveground to belowground. In contrast, prolonged increases in rates of vegetative spread occurring at smaller scales (e.g. within gaps) might have resulted from increased growth rates or larger sizes of clones.

Pages

152

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