El Yunque National Forest

Natural Resources

Although the El Yunque National Forest (EYNF) is one of the smallest forests in the National Forest System, (28,000 acres or roughly 11,300 hectares), it is one of the most biologically diverse areas that the agency manages. The EYNF contains over 240 species of native trees, of which 88 are rare and 23 are only found in the Forest. Along with the trees, the EYNF includes 50 species of native orchids and over 150 species of ferns. This relatively small land area also supports 127 species of terrestrial vertebrate (land animals with backbones) and 10 species of aquatic invertebrates (water animals without backbones).

Water Cycle

Why is there so much rainfall in the El Yunque National Forest? Most of the rainfall in the EYNF is orographic (associated with mountains) in nature. Moisture-laden air is carried by wind and forced to ascend over the mountains. The rise in elevation cools the air, causing condensation in the form of rain.

Trade winds that originate off the African coast and sweep across the Atlantic Ocean bring the EYNF most of the rain that falls between the months of May and November. Depending on their intensity and speed, these winds can produce a few clouds to several days of cloudy and rainy weather, and occasionally hurricanes. Most of the rain falls as the wind rises over and along the east-west mountain axis. More rain falls on the Luquillo mountains (where the EYNF is located) in the eastern part of the island than the western part, because the moisture-laden trade winds first ascends the eastern slopes. The northern slopes of the mountains also receive more rainfall than the southern slopes, because their gradual rise to the peaks serves as a natural catchment area. The southern slopes tend to descend more abruptly to the sea.

For more information:
http://pr.water.usgs.gov/public/rt/pr/rtmap_pr_east.html
El Yunque NF - World Water Day 2008 Presentation

Hurricane Regeneration

Changes in forest composition and structure are apparent after natural disturbances; none cause more significant changes than hurricanes. As many researchers have concluded, hurricanes are the main organizing force of our forest. The Forest goes through a cycle that averages sixty years, starting with great impact by winds and rain of a hurricane, and then sixty years of re-growth. In those sixty years of re-growth, complete changes in the species that dominate the landscape can occur. By measuring changes in tree growth rate, density and size, researchers have observed how the forest can incorporate the energy of the hurricane. Although, the hurricane appears destructive, it is in fact constructive, because it makes the area more productive; it rejuvenates the forest.

For more information:
http://water.usgs.gov/pubs/FS/FS-040-99

Forest Vegetation

The Forest is commonly divided into four forest vegetation types that are characterized by different variations in climate, soil, slope and the dominant tree species it is named after.

The Tabonuco Forest Type

Characterized by the tall trees and low light intensities at ground level. The Canopy trees tend to have very straight trunks with their first branches high above the ground. This forest type contains the richest flora on the Forest with 175 tree species. This zone appears on the foothills and slopes below 2,000 feet (609.6 meters) in elevation, which covers some 5,430 hectares (13,417acres) of the EYNF.

The Palo Colorado Forest Type

Is in essence, an upland swamp of short-statured trees with shallow root systems that begin to occur uphill from the Tabonuco Forest. This forest type has an elevation of above 2,000 feet, on gentle slopes and valleys; and contains 50 tree species. This area of this type covers 3,400 hectares (8,401 acre) of the EYNF.

The Sierra Palm Forest Type

Flora in this area does not normally attain great height or large trunk diameters, but it occurs in dense patches within the elevation ranges of both the Palo Colorado and Tabonuco Forest types. Sierra Palms succeed where other tree species cannot; thus this forest type is found on steep slopes, unstable soils and streambeds above 1,500 feet (457 meters). This forest type covers 2,050 hectares (5,065 acres) of the El Yunque National Forest.

The Dwarf Forest Type

Also known as “elfin woodlands” they are found at the upper edges of the Palo Colorado and Sierra Palm Forest Types, near the ridge tops. In this area tree types become shorter, blending into a zone of stunted vegetation. This forest type exists in a zone of water-saturated soils deficient in oxygen. Most mineral inputs for plants become dissolved in the rain and fog. This forest type covers 450 hectares (1,111 acres) on the EYNF.

For more information:
http://luq.lternet.edu

For more valuable information about the Puerto Rican Flora visit the New York Botanical Garden Virtual Herbarium. Here you will find The Flora Borinqueña Digital Herbarium and Library which presents the scientific work of Nathaniel and Elizabeth Britton, founders of The New York Botanical Garden. The Brittons and their collaborators carried out 16 expeditions to Puerto Rico, during which they collected 10,139 specimens, resulting in 38 new species of flowering plants, lichens, fungi and algae.

USDA Forest Service - El Yunque National Forest
Last Modified: Thursday, 04 December 2008 at 13:34:57 EST