Date of Award

12-2009

Degree Type

Thesis

Degree Name

Master of Science

Major

Geography

Major Professor

Sally P. Horn

Committee Members

Kenneth H. Orvis, Henri D. Grissino-Mayer

Abstract

Key Deer Pond (24° 42' 29.50" N, 81° 22' 36.12" W; ca. 2 m elevation) is a small freshwater pond in a solution hole located within the pine rocklands of the National Key Deer Refuge on Big Pine Key, Florida. Overlapping sediment core sections and a surface grab sample from Key Deer Pond were subjected to pollen, microscopic charcoal, and loss-on-ignition analyses to investigate late-Holocene climate, fire occurrence, and vegetation-fire relationships in pine rockland ecosystems. Macroscopic charcoal from the uppermost meter of the profile was studied to provide a more detailed history of local fire occurrence.

The results from the microscopic charcoal analyses show that fire has long been a part of these pine rockland ecosystems. Generally higher values for all microscopic charcoal indices since ca. 1200 cal yr BP suggest increased fire in the region, and likely around Key Deer Pond. The high-resolution macroscopic charcoal, which spans the last ca. 400 years, provides compelling evidence for repeated fires surrounding the pond. This finding is consistent with the interpretation that lower Keys pine rocklands are a fire-dependent ecosystem characterized by frequent surface fires. The very late human colonization of Big Pine Key, perhaps occurring no more than 160 years ago, suggests that early fires were lightning-induced, and that changes in fire occurrence were the result of prehistoric climate shifts.

Pollen assemblages reveal that the vegetation at the site has changed only moderately since 1660 cal yr BP. Pine dominance over much of the record indicates that pine has long been abundant in the area. Increases in pollen of Conocarpus erectus since ca. 357 cal yr BP, and decreases in the abundance of pine since ca. 83 cal yr BP, may signal the impacts of rising sea level.

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