Doctoral Dissertations

Date of Award

12-2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geography

Major Professor

Sally P. Horn

Abstract

This dissertation investigates past and present environments of the highlands of the Dominican Republic using paleoecological and modem ecological techniques. The relatively unstudied highlands (>2000 m) of the Cordillera Central are blanketed by a mosaic of pine forests, open pine woodlands, and grasslands, with broadleaf trees joining the canopy in sheltered locations. My research on modem vegetation and fire ecology, and on long-t� fire and vegetation history, helps fill gaps in the knowledge of Caribbean environments, and may assist land managers in conservation efforts in the Dominican highlands. A study of the relationship between modem pollen rain and vegetation cover in the highlands provided a basis for interpreting pollen assemblages in sediment profiles. As expected, pine pollen dominated most samples. Detrended Correspondence Analysis indicated that the modem pollen spectra of forested uplands and open wetland sites are clearly distinct, while a variety of other site types that are intermediate in terms of vegetation are also intermediate in terms of modem pollen spectra. Forested sites were widely dispersed, while intermediate sites and wetlands were more tightly clustered, indicating greater similarity in pollen spectra of those sites. Lack of pine stomata was an excellent indicator of treelessness. The distinction between forested and non-forested sites may be useful in interpreting highland fossil records that may reach back into the last glacial period. Analysis of a 126.5 cm sediment core from a bog in Valle de Bao on the windward slope of the Cordillera Central indicated that disturbances by fire, tropical storms, and climatic fluctuations have been part of the highland ecosystem for millennia. The bog formed during a relatively moist period around 4000 yr BP. The record includes strong signals of dry periods during the late Holocene, and matches some trends in a sediment record from Lake Miragoane, Haiti, near sea level. A study of postfire regeneration of pines and shrubs at five recently burned sites provided evidence that the woody vegetation of the pine-forested highlands is well adapted to fire. Most shrubs at all sites resprouted from their bases, and in one site, shrubs regained prefire stem heights within seven years. Recovery of shrub stein .diameters lagged behind. Large pines can survive fire, but in this study, no trees <13 cm in diameter survived. Repeated fires may create and maintain a shrub-dominated · landscape.

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