El Yunque National Forest

El Yunque National Forest (Bosque Nacional El Yunque) is a forest reserve in northeastern Puerto Rico. It is the only tropical rainforest in the United States National Forest System.

This forest, formerly known as the Caribbean National Forest, is commonly known simply as "El Yunque," which may be attributed to either a Spanish approximation of the aboriginal Taíno word yu-ke which means "white lands," or the word "anvil," which is Yunque in Spanish.

The island of Puerto Rico was formed by volcanic activity during the Triassic period. Thrusting out of the Caribbean Sea, it had no land bridge to any continent. Consequently, the animals of Puerto Rico (and El Yunque National Forest) originally arrived on the island by either swimming, floating or flying. They thus were smaller in size than those found on large continents.

High annual rainfall (over 20 ft a year in some areas) creates a jungle-like setting with lush foliage, crags, waterfalls, and rivers. The second-tallest mountain in El Yunque is also named El Yunque.

El Yunque National Forest is located on the slopes of the Sierra de Luquillo mountains, encompassing 28,000 acres (43.753 sq mi or 113.32 sq km) of land, making it the largest block of public land in Puerto Rico. The highest mountain peak in the forest rises 3,494 ft (1,065 m) above sea level.

The rainforest has several trails from which the jungle-like territory's flora and fauna can be appreciated. El Yunque is also renowned for its unique Taíno petroglyphs.

Because Puerto Rico is south of the Tropic of Cancer, it has a tropical climate. El Yunque has no distinct wet or dry season; it rains year-round. As a result, the temperature and length of daylight remain relatively constant throughout the year.

The average temperatures in the summer are 26 °C (80 °F) high and 20 °C (68 °F) low. In the winter, the average temperatures are 22 °C (72 °F ) high and 15 °C (58 °F) low. In addition, temperatures can drop below 10 °C (50 °F) on clear nights during the winter but never below freezing. All of these factors provide a year-round growing season.

The rainforest ecosystem is exposed to constant cloud cover, and persistent winds produced by the adiabatic process of air particles rushing up through the mountainside have affected the morphology of El Yunque.

El Yunque is composed of four different forest vegetation areas:

• Tabonuco Forest

• Palo Colorado Forest

• Sierra Palm Forest

• Dwarf Forest

The dwarf forest ecosystem is located at around 910 m (3,000 ft) and composes the smallest sub-region in El Yunque. The forest is characterized by a variety of vegetation only found in Puerto Rico.

The vegetation shows stunted growth in which the trunk's diameter is widened, and the number of leaves on the branches is lower than expected. Other specific factors that affect this sub-region's growth are the high acidity level and poor water runoff from the soil.

Although many species have adapted to these harsh environments, five species frequent the dwarf forest: Ocotea spathulata, Tabebuia rigida, Calyptranthes krugii, Eugenia borinquensis and Calycogonium squamulosum. Another abundant type of plant in the dwarf forest is epiphytes.

El Yunque supports a vast array of animal and plant life that varies depending on the altitude range in the rainforest. However, the great competition in the canopy does not allow lower-level plants to develop and prosper.

The characteristic of having a widened tree trunk is ideal for epiphytes that require a host to live. Therefore, a substantial amount of epiphytic plants have cemented their existence in the flora of El Yunque, specifically in the dwarf forest, due to the moisture, precipitation and protection from the sun.

Although the El Yunque National Forest is one of the smallest forests in the U.S. National Forest System (roughly 11,300 ha or 28,000 acres), it is one of the most biologically diverse areas the agency manages.

El Yunque National Forest contains over 240 species of native trees, of which 88 are rare and 23 are only found in this forest. Along with the trees, the El Yunque National Forest includes 50 species of native orchids and over 150 species of ferns.

This relatively small land area also supports 127 species of terrestrial vertebrates (land animals with backbones) and ten species of aquatic invertebrates (water animals without backbones).

The El Yunque National Forest is the habitat of five endangered species (meaning they may die out in a short time) and one threatened species (meaning it has the potential of dying out over a long time).

• The Puerto Rican Parrot (Amazona vittata) is one of the ten rarest birds in the world and is only found on the Island of Puerto Rico. It is a small parrot that measures 28 - 30 cm (11 - 11.8 in). Its coloring is predominantly green, with a red forehead and white rings around the eyes. The species is the only remaining native parrot in Puerto Rico.

  The island parrot population was estimated to number in the hundreds of thousands when first encountered during Columbus' second voyage of discovery. However, it dropped to a low of 13 birds in 1975. After this date, the population reached an estimated 47 birds in the wild, declining again to 23 birds after Hurricane Hugo in 1989. Currently, the wild flock is climbing, but the challenges are many, and its future still hangs in the balance.

  There are 79 adult birds in captivity in the aviaries of the El Yunque National Forest and Rio Abajo State Reserve. The remaining parrots and their nesting habitat are constantly monitored and managed through a cooperative effort between the Forest Service, the U.S. Fish and Wildlife Service, and the Puerto Rican Department of Natural Resources.

• The Puerto Rican Boa (Epicrates inornatus) is found throughout the island and lives in El Yunque below an elevation of 365 m (1200 ft). Although the recovery plan for the boa was approved in 1986, its ecology is only now being understood through research conducted by the USDA Forest Service International Institute of Tropical Forestry.

• The Puerto Rican Broad-winged Hawk (Buteo platypterus brunnescens) is a subspecies of the broad-winged hawk and is found in isolated mountain areas preferring to hunt from lofty perches. This hawk's prey consists of frogs, lizards, other birds and insects.

  As of 1992, the population on the island was estimated at approximately 124 individuals. Its decline has been due to forest destruction and habitat loss due to construction.

• The Puerto Rican Sharp-shinned Hawk (Accipiter striatus venator), another subspecies of the sharp-shinned hawk, is a small forest hawk. Currently, it is restricted to five isolated mountain-forest areas. Primarily it feeds on small birds. If one is fortunate, it may be seen streaking by in the forest. Nest failures, deforestation and habitat loss due to construction have played a significant role in the decline of this species.

Approximately 16 species of common coqui, members of the diverse neotropical frog genus Eleutherodactylus, are known in Puerto Rico. Of these, 13 have been found in El Yunque National Forest.

This tiny frog earned its Puerto Rican common name due to the call of the most common coquí species in Puerto Rico, Eleutherodactylus coqui, which begins as the sun sets and ends in the early dawn. This has made it an animal of great endearment to Puerto Ricans.

Although the coquí is an amphibian, it possesses some unusual features in frogs. These differences are seen mainly in its morphology, reproduction and developmental stages. In terms of morphology, the coquí does not have webbing between its toes because it is a tree dweller in moist environments.

Another significant difference is that it does not have a final larval stage, and the eggs laid by the female are terrestrial instead of aquatic. This means that a miniature froglet, rather than a tadpole, arises from the incubation period.

Neotropical migrant birds breed in North America and migrate to the south for the winter. Approximately 35 species of these migratory birds either winter or pass through El Yunque during this season. They contribute significantly to the total animal diversity of the forest. The recent decline in the population of migratory birds throughout North America, Mexico, Central America and the Caribbean is of growing concern.

Significant causes of declines in the populations of many of these species are believed to stem from the fragmentation of North American breeding habitats; also the loss of wintering habitats in Mexico, Central and South America, and the Caribbean.

Rivers and streams provide aquatic habitats for organisms essential to the forest's biological diversity. Most perennial (flowing year-round) and many ephemeral (flowing for short periods yearly) streams in the forest support many aquatic species.

Aquatic species include seven species of fish, nine species of freshwater shrimp and one species of freshwater crab. The forest's aquatic resource values are significant for ecological and recreational reasons.

Some of the island's most pristine and productive aquatic habitats remain within the forest boundary. These nonrenewable resources are illegally fished with traps and spears. Harvest of these species is unregulated, both on and off the forest.

Monitoring surveys to determine their distribution, habitat needs, population status and trends are conducted regularly to protect these aquatic members of the forest's family.