Biodiversity in Puerto Rico

Biodiversity in Puerto Rico
From: Endangered Species Bulletin
Date: November 1, 1998
Author: Silander, Susan

Commonwealth agencies have partnered with US and Caribbean conservation organizations to protect rare and endangered plant and wildlife species on Puerto Rico. Around 5% of the island has been declared as reserves or refuges. Nearly 80 species have been listed as endangered or threatened, and an additional 500 have been labeled as critical.

The primary threats facing the island's native flora and fauna are habitat destruction and modification, illegal hunting or capture, and the introduction of exotic species. At present, 78 species of plants and animals are federally-listed as threatened or endangered. This concludes 3 species of amphibians, 11 reptiles, 11 birds, 5 mammals, and 48 plants. Of these 78 species, 56 are known only from Puerto Rico, The Puerto Rico Department of Natural and Environmental Resources has listed 90 plants and animals as threatened or endangered, and it maintains a list of over 500 plant species whose status is considered critical.

The island of Puerto Rico is part of the archipelago of over 1,000 islands known as the West Indies, a chain that separates the Caribbean Sea on the south from the Atlantic Ocean to the north. Approximately 110 miles (160 kilometers) long and 35 miles (55 km) wide, Puerto Rico has more than 300 miles (483 km) of coastline. The Commonwealth of Puerto Rico also contains two other inhabited islands and a number of small, uninhabited islands. The wide variety of habitats found in these islands has produced a rich diversity of plant and animal life, including species found nowhere else.

The main island of Puerto Rico is volcanic in origin, and its topography is rugged. Puerto Rico can be divided into several major physiographic regions: the central mountains ("Cordillera Central"), the Luquillo Mountains ("Sierra de Luquillo"), the limestone region ("Calizas" or "Mogotes"), and the coastal plains ("Llanos Costeros"). Elevations reach 4,390 feet (1,338 meters) at Cerro Punta in the central mountains, from which more than 100 rivers and streams flow to the sea. Rainfall on the island, despite its small size, is not evenly distributed. Because of differences in topography and the effect of the easterly trade winds, rainfall can range from more than 100 inches (250 centimeters) at the summits of the central mountains to as little as 30 inches (75 cm) in the southwestern region. Rainfall patterns and geologic formations have resulted in a wide variety of soils and vegetation types. The island's vegetation has been classified according to the Life Zone system (Ewel and Whitmore 1973) as subtropical dry forest, subtropical moist forest, subtropical wet forest, subtropical rain forest, lower montane wet forest, and lower montane rain forest.

The karst region of northwestern Puerto Rico has been described as one of the best of its kind in the Caribbean. This area of porous limestone abounds with caves, sinkholes, and underground rivers. An excellent example of subtropical dry forest can still be found on the island's southwestern coast, largely within the Guanica Commonwealth Forest. This forest type is rapidly being destroyed elsewhere in the region. The Caribbean National Forest, where dwarf or cloud forests grow on the peaks of the Luquillo Mountains, is the only tropical forest in the U.S. national forest system, and is currently home for the only known wild flock of the endangered Puerto Rican parrot (Amazona vittata). Mona Island, an uninhabited island between Puerto Rico and the Dominican Republic, is bounded by cliffs that rise 200 feet (60 m) from the sea to a plateau covered with subtropical dry forest. Formerly the home of Taino Indians, pirates, guano miners, and treasure hunters, it harbors species found on no other island.

As with many other Caribbean islands, Puerto Rico has been, and continues to be, heavily affected by the influence of humans. Agriculture reduced some forests in the 16th and 17th centuries, but in the 18th century massive deforestation took place to clear land for crops such as sugar cane, coffee, and tobacco. Coffee, at that time planted in the shade, was grown primarily in the central mountains. In the early 19th century, sugar cane became the island's principal crop and its cultivation destroyed most of the forests on the coastal plain. Later, as the sugar industry declined and the population shifted away from rural areas, much former agricultural land was developed for urban and industrial uses. One by-product of this change was the regrowth of secondary forests in areas such as the central mountains. Nevertheless, urban, industrial, and tourist development, along with changes in agricultural techniques such as the planting of sun-dependent coffee, threaten many of the rich natural resources that still remain.
Approximately 5 percent of the island is protected either as public forests or reserves managed by the U.S. Forest Service (Caribbean National Forest) and the Puerto Rico Department of Natural and Environmental Resources (with its system of 15 public forests), as refuges managed by the U.S. Fish and Wildlife Service (FWS), and as land protected by non-governmental organizations. These forests contain an excellent representation of the diverse ecosystems once found widely on the island.

The native avifauna includes 239 species, of which 14 are endemic to Puerto Rico. (Another two are also found in the U.S. Virgin Islands.) Six of these endemic species are federally-listed as endangered (Raffele 1989, Raffele et al. 1998). Of the 63 species of land reptiles and amphibians occurring in Puerto Rico, 42 occur nowhere else, and 14 of the rest are restricted to Puerto Rico and the U.S. Virgin Islands (Rivero 1998). Fourteen of the 63 reptiles and amphibians are listed as either threatened or endangered.

The native flora of Puerto Rico consists of about 3,000 species, of which about 8 percent are endemic. When considering only trees, Puerto Rico and the Virgin Islands harbor about 550 native species, of which 142 (or 26 percent) are endemic (Liogier and Martorell 1982). As of September 30, 1998, the FWS listed 669 plant taxa worldwide as either threatened or endangered, of which 48 (or 7.2 percent) are from Puerto Rico, even though this island contains only 0.09 percent of the total land area of the United States. Most of these listed plants are found either in the northern karst region or on the dry southern coast, two areas under pressure for development.

The FWS staff in Puerto Rico works with Commonwealth agencies such as the Puerto Rico Department of Natural and Environmental Resources, universities, and non-governmental organizations for the protection and recovery of threatened and endangered species. Because of Puerto Rico's geographical and cultural ties to the Caribbean, partnerships with neighboring island countries are essential. Through our cooperative efforts, we are making strides towards recovery that our agency could not achieve on its own.

References
Ewel, J. and J.L. Whitmore. 1973. Ecological life zones of Puerto Rico and the Virgin Islands. U.S.D.A. Forest Service Research Paper ITF-18. 72 pp.
Liogier, H.A. and L. F. Martorrell. 1982. Flora of Puerto Rico and adjacent islands: A systematic synopsis. Editorial de la Universidad de Puerto Rico, San Juan, Puerto Rico. 342 pp.
Raffaele, H.A. 1989. A guide to the birds of Puerto Rico and the Virgin Islands. Princeton University Press, Princeton, New Jersey. 254 pp.
Raffaele, H.A., J. Wiley, O. Garrido, A. Keith, and J. Raffaele. 1998. A guide to the birds of the West Indies. Princeton University Press, Princeton, New Jersey. 511 pp.
Rivero, J.A. 1998. Los anfibios y reptiles de Puerto Rico. Segunda Edicion Revisada. Editorial de la Universidad de Puerto Rico. 510 pp.
Susan Silander is a Botanist with the FWS Caribbean Office in Puerto Rico.