Doctoral Dissertations

Date of Award

5-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geography

Major Professor

Henri D. Grissino-Mayer

Committee Members

Sally P. Horn, Carol P. Harden, Jennifer A. Franklin

Abstract

Pine rocklands are globally endangered, fire-maintained communities currently restricted to small habitat areas in southern Florida, Cuba, and the Bahamas. The purpose of this dissertation research was to identify the long-term ecological disturbance regimes and climatic trends responsible for the persistence of pine rocklands, and examine how human-induced changes during the 20th century contributed to decline of these communities. This research applied techniques of dendrochronology in extreme southern Florida, in a subtropical region where tree‐ring science has never been applied, to increase the understanding of how anthropogenic and natural disturbance events have decreased the spatial distribution of South Florida slash pine (Pinus elliottii Engelm. var. densa Little and Dorman; hereafter slash pine), the foundation species of pine rocklands.

To investigate the complex dynamics of declining pine rockland communities, I analyzed (1) the dendrochronological potential and climate response of slash pine, (2) the intra-annual ring formation characteristics and relationships to monthly climatic conditions, (3) the influence of historical fire regimes and varied fire management practices since the 1950s on the structure of slash pine savannas on adjacent islands in the Lower Florida Keys, and (4) the control of global-scale oceanic/atmospheric oscillations on historical wildfire occurrence.

The analyses presented here demonstrate that slash pine forms anatomically distinct, annual growth rings with the consistent year-to-year variability necessary for rigorous dendrochronological studies. Annual radial growth of slash pine is primarily influenced by water availability during the growing season; however intra-annual cellular growth is driven by daily insolation. In the Lower Florida Keys, the growing season of slash pine occurs between February and November, with trees experiencing dormancy between November and January. Reconstructions of fire history and savanna structure revealed that, over the past 150 years, frequent fires occurring every ca. 6 years promoted pine recruitment and ensured the persistence of pine rockland habitat. However, the recent lack of fire in some areas could result in the loss of pine rockland habitat, as pine savannas are currently succeeding to tropical hardwood hammock. Over the past several centuries, interacting effects of two Pacific climatic forcing mechanisms (El Niño-Southern Oscillation, Pacific Decadal Oscillation) drove wildfire occurrence in the Lower Florida Keys.

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