Identifier

etd-01202011-180121

Degree

Doctor of Philosophy (PhD)

Department

Biological Sciences

Document Type

Dissertation

Abstract

Resprouting and reseeding shrubs are predicted to be restricted to habitats with long and short return intervals of natural disturbances, respectively. Nonetheless, resprouters and reseeders co-occur along Gulf of Mexico coastal ecoclines where lightning-ignited fires were historically frequent. In this collection of studies, I examine fire responses, habitat associations, distribution limits, and seedling recruitment of Hypericum species along ecoclines in pine savannas of the St. Joe Bay State Buffer Preserve in Gulf County of Florida. In this area, ecoclines are characterized by topographic, soil moisture, and fire heterogeneity gradients. Hypericum microsepalum, an obligate resprouter, primarily resprouts following disturbances that remove aboveground stems. It is associated with upland, dry habitats that frequently burn, but can survive over a wide range of habitats along ecoclines. Hypericum chapmanii, an obligate reseeder, is killed by fires and recruits with a pulse of seedlings. Hypericum brachyphyllum, a facultative reseeder/resprouter, both reseeds and resprouts after low intensity disturbances, but only reseeds after high intensity disturbances. Hypericum brachyphyllum and H. chapmanii are associated with intermediate, mesic areas along ecoclines where fires become increasingly heterogeneous to rare as they move down slopes. These species have low survival outside of their original habitats. Direct effects of fire, specifically removal of aboveground biomass and litter, increase seedling recruitment of H. brachyphyllum and H. chapmanii. Fires have no direct effect on the growth of H. brachyphyllum to juvenile and reproductive adult stages, but indirectly increase growth of H. chapmanii. This is likely the result of fire facilitating regeneration of associated nurse plants. Therefore, fires are important for seedling recruitment and growth of Hypericum species. Time to reproduction is longer for H. chapmanii (3+ years) and H. brachyphyllum (3 years) than H. microsepalum (2 years). Differences in time to reproduction should cause species to segregate along a fire frequency gradient. I thus conclude that heterogeneous fires within a high fire frequency landscape may increase persistence of Hypericum resprouters and reseeders in higher and lower areas along ecoclines, respectively. It should also allow plants with different life histories to co-occur in intermediate areas along ecoclines where fires are patchy and vary in intensity.

Date

2011

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Platt, William J. , III

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