Doctoral Dissertations

Chengxia You

Date of Award

12-1991

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

J. Frank McCormick

Committee Members

Clifford Amundsen, Edward Buckner, Frank Woods

Abstract

Objectives of this ecological life cycle study are to identify population properties and environmental factors which influence population dynamics of Manilkara bidentata, a primary canopy tree species in the Luquillo Experimental Forest (LEE) of Puerto Rico. Factors which most strongly influence Manilkara population distribution and abundance are: 1) long range seed dispersal (> 100 meters) by bats to favorable habitats, 2) long term (40 yrs) persistence of seedlings in closed canopy forests, and 3) rapid and effective acclimatization of seedlings to increased light following forest disturbances (4x and 24x increase in seedling height growth rates in small and large gaps respectively). All these factors contribute to relatively high survival rates from seedling to sapling size classes. The transition from seedling to sapling size class is the most critical stage in the life cycle. Hurricane disturbance is the most important exogenous event influencing Manilkara population dynamics. Fluctuations of age-classified density, biomass, and nutrient distribution of Manilkara populations are "stamped with the brand" of hurricane cycles. A population matrix simulation model supports interpretations of field data which indicate that one consequence of hurricane disturbance is a reduction of seedling mortality rates. This reduction is probably a consequence of the release of seedling growth from suppression under forest shade conditions.

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