The NSS Bulletin - ISSN 1090-6924
Volume 39 Number 3: 73-79 - July 1977
A publication of the National Speleological Society

Isolation of a Plant Community by Karst Processes in Southwestern Puerto Rico
Barbara B Cintrón and Barry F. Beck

Abstract

The central mountain chain trending east-west across Puerto Rico is flanked on the north and south by off-lapping Teritary sedimentary rocks, principally limstones. The Quebrada de Los Cedros is a deep, vertically-walled, karst gorge located in the semi-arid southeastern corner of the island. A genetically related cave-spring system underlies it. Temperatures within the gorge are 6 to 8°C cooler than in the surrounding hills and the relative humidity is 12 to 18% higher.

The surrounding hills contain plant species typical of the subtropical dry forest life zone: Bursera simaruba, Thouinia portoricensis, Coccoloba microstachya, Bourreina dominguensis and Colubrina arborescens, along with the shrubs Croton rigidus, Lantana involucrata and the liana Stigmaphyllon periplocifolium. Bucida buceras, a tall tree, is often found in the valleys. The vegetation is less than 10 m tall and is dense, with many thorns and small, thick mostly deciduous leaves. Below the shrub layer, the forest floor is generally bare. The plant assemblage of the gorge, in contrast, is considerably taller (about 20 m) with large, thin, membranous leaves, and a dense ground cover of mosses and ferns. Andira inermis, Guarea trichiloides, and Dendropanax arboreus are common trees here but are generally typical of moist forest at higher elevations. Tectaria martinicensis, Adiantum tenerum and Dennstaedtia adintiodes are frequently observed ferns. Ficus citrifolia, F. trigonata, and Clusia rosea are common on the gorge walls and their aerial roots intertwine with the woody vine Trichostigma actandrum, forming dense tangles on the gorge floor. Only 45% of the known flora of the Quebrada de Los Cedros is commonly found in the surrounding areas. The deep, verticaly walled gorge and the underlying El Convento Cave-Spring System, both features resulting from karst processes, have caused this shaded, cool, moist environment with its characteristic vegetation.

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