Puerto Rican dry forests

Puerto Rican dry forests are subtropical dry forests located in southwestern and eastern Puerto Rico and on the offshore islands.Ewel, J.J. and Whitmore, J.L. (1973) The ecological life zones of Puerto Rico and the U.S. Virgin Islands. USDA Forest Service, Institute of Tropical Forestry, Rio Piedras, Puerto Rico.] These forests grow in areas receiving less than 1000 mm of rain annually. Many of the trees are deciduous, losing their leaves during the dry season which normally lasts from December to July.Murphy, P.G., Lugo, A.E., Murphy, A.J., Nepstad, D.C. (1995) The dry forests of Puerto Rico's south coast. Pp. 178-209 "in" A.E. Lugo and C. Lowe (editors) "Tropical Forests: Management and Ecology". Springer-Verlag, New York.]

Distribution

Dry forests exist in two areas on the island of Puerto Rico - along the south coast of the island (in the dry orographic rain shadow of the Cordillera Central) and in the northeastern corner of the island near Fajardo, where the combination of low elevation and strong winds off the ocean (Northeast Trade Winds) result in a dry environment. Dry forests also exist on the adjacent off-shore islands of Vieques, Culebra, Mona, Monito, Desecheo, Caja de Muertos and Cayo Santiago.

The vast majority of studies have focused on the south coast - almost nothing has been published about the northeastern dry forest. Studies of the offshore islands have been limited to species lists and qualitiative descriptions of the vegetation.

Ecology

Puerto Rican dry forests (like Caribbean dry forests in general) consist of short-stature (usually <5 m tall), multi-stemmed trees. The canopy is largely evergreen (dominated by "Gymnanthes lucida" (Euphorbiaceae) in areas of limestone soil), while the emergent layer is considerably more dry-season deciduous.Lugo, A. E., J. A. Gonzalez-Liboy, B. Cintrón, and K. Dugger. (1978) Structure, productivity and transpiration of a subtropical dry forest in Puerto Rico. "Biotropica" 10:278-291.] Murphy, P. G., and A. E. Lugo. (1986) Structure and biomass of a subtropical dry forest in Puerto Rico. "Biotropica" 18:89-96.]

Although most of the forest was destroyed for agriculture prior to the 1940s, some patches of forest which pre-date that period still exist. Areas that were used for charcoal production or for fence-posts have recovered rapidly - after 50 years forests that had been used for charcoal production recovered to the point where they were indistinguishable from much older forests.Molina Colón, S. (1998) Long-term recovery of a Caribbean dry forest after abandonment of different land uses in Guánica, Puerto Rico. Ph. D. University of Puerto Rico, Rio Piedras.]

In addition, large areas of secondary forest have grown back on abandoned agricultural land. Unlike areas which were only lightly used, these forests on abandoned farmland have far fewer species than do natural forests. Their path to recovery remains uncertain.

Puerto Rican dry forests are dominated by plants in the Rubiaceae, the Euphorbiaceae and the Myrtaceae. In this regard they are similar to Jamaican dry forests, but differ sharply from dry forests on the mainland of South and Central America which are dominated by the Fabaceae and the Bignoniaceae. [Gentry, A.H. (1995) Diversity and floristic composition of neotropical dry forests. Pp. 146-194 "in" S.H. Bullock, H.A. Mooney and E. Medina (editors) "Seasonally Dry Tropical Forests". Cambridge University Press, Cambridge.]

The best example of dry forests in Puerto Rico (and probably, in the Caribbean as a whole) are in the Guánica State Forest ("Bosque Estatal de Guánica") outside the town of Guánica. This site has also been the focus of the vast majority of studies of dry forests.

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