Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

William J. Platt

Abstract

The objective of this dissertation was to characterize the role of hurricanes in the dynamics of old-growth Southern Mixed Hardwood Forests from the coastal plain of the northern Gulf of Mexico. First, we used data from five stands to describe the structure, composition, and disturbance regime of these forests. All five stands have Magnolia grandiflora and Fagus grandifolia among the dominant species, and have been affected by frequent but relatively mild hurricanes (4-6 per century, windspeed $<$200 km/h). Second, we examined the changes in tree recruitment, growth, and mortality occurred in Woodyard Hammock, northern Florida, after this forest was affected by Hurricane Kate in 1985. The analysis was based on data from biennial censuses of a 4.5 ha plot conducted between 1978 and 1992. Hurricane Kate produced extensive canopy disruption but limited tree mortality. This disturbance prompted a phase of increased recruitment, growth, and survival of understory trees, and decreased growth and survival of overstory trees. Release of small understory individuals appeared to be critical for the persistence of three short-lived dominant species, Pinus glabra, Ostrya virginiana and Carpinus caroliniana. However, persistence of the longer-lived dominants Magnolia grandiflora, Fagus grandifolia, Liguidambar styraciflua, Nyssa sylvatica, and Ilex opaca, appeared to depend primarily on resistance to hurricane damage. Third, we used matrix population models to test specific hypotheses about mechanisms of persistence of F. grandifolia in Woodyard Hammock. These models showed that, both before and after Hurricane Kate, this population was close to equilibrium. This result supported the hypothesis that persistence of F. grandifolia has resulted from hurricane resistance. Sensitivity analyses of the models suggested that the key for hurricane resistance has been the high survival of medium-size trees. Life-history strategies involving resistance and survival to hurricane disturbance, rather than release and rapid growth, appear to have been prevalent in these forests. However, the hurricane regime would have resulted in coexistence of species with the two types of strategy. Hurricanes would have been frequent enough to secure the persistence of species dependent on release, and mild enough not to compromise that of species dependent on resistance.

ISBN

9780591288865

Pages

135

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