The island of Vieques is in the West Indies about seven miles east of Puerto Rico. Although part of the Commonwealth of Puerto Rico politically, geographically Vieques is one of the Virgin Islands.
The term West Indies includes all of the islands of the Caribbean Sea. These in turn can be divided into the Greater Antilles and the Lesser Antilles. The Greater Antilles are the four large islands in the northwestern portion of the Caribbean – Cuba, Hispaniola (Haiti and the Dominican Republic), Jamaica, and Puerto Rico. The Lesser Antilles include the smaller islands of the Caribbean – beginning with the Virgin Islands and continuing into the Leeward and Windward Islands.
Geologically, Vieques is a small, exposed ridge of the sub-marine mountain range that creates the entire sweep of the West Indies. This chain of mountains begins with Cuba and ends with Grenada, near the coast of Venezuela.
The islands began forming over 100 million years ago, and the long process of undersea mountain building eventually brought sub-marine ridges and peaks to the surface. Volcanos alternated with coral reef deposits and changing sea levels to create the islands as we see them now. The engine for these changes has been the shifting tectonic plate that lies beneath Central America and the Caribbean basin. The relatively small Caribbean Plate is being squeezed between the massive North and South American plates, and the Cocos Plate is pushing from the west. This combination is causing the Caribbean Plate to slowly creep eastward.
Even today Vieques shows obvious signs of it's volcanic history. The western end in particular is peppered with huge, isolated boulders that seem to have been dropped from the sky.
Vieques is definitely a tropical island, it's actually much closer to Venezuela than to Miami. Daily temperatures are very predictable, they usually run from 85°F during the day down to 75°F at night. The biggest difference between winter and summer is not the daytime high, although summer is a few degrees warmer, rather it's the range between the day and night temperatures. During the winter, nighttime temperatures usually drop 10° or more. During the summer the difference might be less than 5°. In 2004 it reached 92°F on one particularly hot day, and it dropped to a nippy 69°F on the coldest night of the year!
The island contains a variety of forest types due primarily to variations in rainfall. As small as the island is, this impact is still noticeable at different locations around the island. These variations extend from an annual rainfall of 45 to 55 inches in the moist forest areas compared to 30 to 35 inches of rain in the drier parts. Soil type, especially in shoreline locations, also determines what types of plants will grow in a particular area.
The moist forest areas are generally found along the island's north facing hillsides on the Atlantic side, particularly toward the Western end of the island. Both evergreen and deciduous trees form a canopy that may exceed 75 feet in height. Trees may include kapok, mango, sandbox, saman, Strangler fig and genip. (All right, I read that somewhere.) Shade tolerant plants such as wild coffee, teyer palm, lime, ferns and mosses form the sub-canopy
The low lying costal areas on the Caribbean or southern side of Vieques represent the dry forest vegetation. Cactuses, grasses, shrubs and thorn bushes predominate here, particularly at the eastern end of the island. The canopy in this forest is lower than in the moist forest.