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FOSS Ecoscenarios: El Yunque National Forest
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INTRODUCTION
Biome: Tropical Rain Forest
In the northern region of the Caribbean Sea, 1,200 kilometers (km) southeast of Florida, lies the
island of Puerto Rico. Nearly 60 percent of the island is covered with mountains. It is also home
to many different ecosystems including hot deserts, mangrove forests, grasslands, freshwater rivers,
coral reefs, caves, and tropical rain forests.
The Sierra de Luquillo Mountains are clustered in the northeastern part of Puerto Rico. Tropical
storms build as they come across the Atlantic Ocean and drop large amounts of rainfall on the
Sierra de Luquillo. The result is a lush tropical rain forest ecosystem.
The tropical rain forest of the Sierra de Luquillo was first protected in 1876, when Puerto Rico
was under Spanish rule. By declaring it a reserve, the Spanish protected the trees so that enemies
could not use their lumber to make ships that might fight against them. It was one of the first
reserves in the Western Hemisphere.
Courtesy of Father Alejandro Sánchez
The canopy of trees in El Yunque forms a green carpet that covers
the mountains, Sierra de Luquillo.
In 1898, Puerto Rico became a self-governing territory of the United States. Eventually the
eastern preserve became part of the US Forest Service. It was ultimately renamed El Yunque
National Forest in honor of the native Tiano people, who called the cloud-shrouded
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mountaintops “yuke,” meaning “white lands.” It is also the name of the tallest mountain in the
Sierra de Luquillo range. El Yunque National Forest covers approximately 113 square kilometers
(km2) of mountainous tropical rain forest.
El Yunque offers many ecosystem services. Worldwide, tropical rain forests cover 2 percent of
Earth’s surface; yet contain 50 percent of all plant and animal species. El Yunque is the only
tropical rain forest managed by the US Forest Service and is home to many species in danger of
extinction like the Puerto Rican Parrot.
Rain forest trees protect nutrients from eroding and provide important buffers from strong
hurricanes. El Yunque is a popular destination for ecotourism, which is tourism that aims to
protect the ecosystem. The ecotourism business produces income for Puerto Rico in a way that is
less destructive than using the forest as farmland or timber.
Humans are adding extra carbon to the atmosphere in the form of carbon dioxide (CO2) by
burning fuels like wood, coal, oil, and natural gas. Increased CO2 in the atmosphere is one cause
of climate change. The massive trees in El Yunque store large amounts of carbon in their biomass
that would otherwise become greenhouse gases in the atmosphere. This important process is
called carbon sequestration.
The primary concern for tropical forests, including El Yunque, is habitat loss and destruction.
Rain forests, and the species that live in them, are being lost rapidly. It is estimated that,
worldwide, each hour about 36 km2 of rain forest are cleared. In the same hour, 6 plant or animal
species go extinct. The preservation of El Yunque National Forest and the recovery of the Puerto
Rican Parrot, which was once on the brink of extinction, are great success stories.
Urban areas continue to grow in Puerto Rico and replace natural habitats. Currently only 8
percent of Puerto Rico is protected. It is much easier to protect wildlife on public lands than on
private lands. But in Puerto Rico, 90 percent of the island is privately owned.
Ecosystem Services
• Air quality maintenance: Rain forests play a major role in filtering air pollution, and extracting
CO2 from the air through photosynthesis.
• Climate Regulation: El Yunque National Forest plays a role in global climate patterns and
reduces the negative effects of natural disasters, such as hurricanes and flooding, in the rest of
Puerto Rico.
• Educational value: The vast biodiversity found within tropical rain forest offers considerable
educational and scientific value.
• Erosion, flood, and storm control: The tall trees of El Yunque act as a buffer from the strong
hurricane winds as storms come ashore. In addition, the root systems keep the precious humus
(an important component of soil) from washing away in heavy rainfall.
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• Food: Many popular foods grow in the rain forest. Coffee beans are products of Puerto Rico
that grow near the rain forest.
• Habitat refuge: Tropical rain forests are home for more than half of the world’s terrestrial
species. El Yunque forms the primary habitat for the endangered Puerto Rican Parrot.
• Natural Resources: Rain forest trees provide many resources such as timber, paper, and
firewood.
• Nutrient cycling: Tropical rain forests receive very few nutrients from the outside and must
produce most nutrients themselves. When left intact, a rain forest acts as a closed-loop system,
recycling the nutrients it has created.
• Primary production: Primary production of trees is important for maintaining the carbon cycle.
• Soil formation: Trees and plants maintain soil quality by helping produce and hold onto humus
(an important component of soil).
• Spiritual experience and sense of place: El Yunque offers a deep sense of belonging, cultural
heritage, and religious and spiritual significance for many people that visit and live near the
forest.
• Tourism: El Yunque is a popular destination for ecotourism. Tourism business produces income
for Puerto Rico in a way that is less destructive than using the forest as farmland.
ABIOTIC DATA
Tropical rain forest ecosystems have heavy rainfall and high temperatures year-round. The
temperature and length of daylight remain fairly constant throughout the year. There are 11–
13.25 hours of light each day throughout the year.
The average air temperature in El Yunque National Forest ranges from 25 degrees Celsius (˚C) to
28°C at lower elevations. The elevations at El Yunque vary from about 100–1000 meters (m).
Temperatures are cooler in the mountains, with highs of only 17°C. All these factors provide a
year-round growing season for producers.
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It rains daily at El Yunque, with slightly more rain in the winter. Clouds coming from the ocean
hit the mountains on the eastern side and drop moisture, while areas to the west of the mountains
receive less. Average annual precipitation is 510 centimeters (cm) per year in the forest. San Juan,
the capital just west of El Yunque, receives only 150 cm of precipitation per year.
Courtesy of National Oceanic and Atmospheric Administration (NOAA)
The map shows the distribution of average annual precipitation across
Puerto Rico. Notice that the highest levels fall in El Yunque forest.
Like most rain forests, El Yunque has clay-like soils that are low in nutrients. Alone, these soils
cannot sustain the lush plants found in rain forests. The massive trees and lush plants maintain the
soil quality by providing organic material, such as leaves and branches. Decomposers quickly
break down this material, creating a nutrient-rich layer of humus that rests on top of the other
soil. Tree roots prevent the humus from being washed away by heavy rainfall. When these trees
are removed, the humus quickly erodes.
Tropical storms and hurricanes frequently pass over Puerto Rico, hitting El Yunque first.
Hurricane season in the Caribbean lasts from June to November. High winds and heavy rainfall
can damage forests. In 1998, Hurricane Georges was especially destructive. Winds blew over 185
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km per hour, knocking down many older trees and destroying buildings. The hurricane caused
over $5 million in damage.
Courtesy of Father Alejandro Sánchez
This opening in the canopy is the result of Hurricane George in
1998. In a few years the surrounding palms will close the gap.
Sometimes it isn’t the winds that cause the most damage. In 2004, Hurricane Jeanne hit Puerto
Rico with relatively mild wind speeds of 130 km per hour. But the storm dumped over 60 cm of
rain on parts of eastern Puerto Rico, causing historic floods. Scientists are concerned that climate
change may result in stronger hurricanes, followed by more frequent drought events, which could
have dramatic effects on El Yunque.
BIOTIC DATA
Annual primary productivity is the amount of energy provided by the producers to the ecosystem
each year. Tropical rain forests like El Yunque have very high annual primary productivity,
because the majority of terrestrial producers worldwide are found in rain forests. The tropical
climate in El Yunque is ideal for large and lush plant growth.
Annual primary productivity is very high in tropical rain forests, like El Yunque, because of the
yearlong growing season.
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The rain forest is dense, with a diverse community of producers ranging from tall trees to vines,
shrubs, and low-growing plants. Like all tropical forests, El Yunque has four distinct layers: the
forest floor, the understory, the canopy, and the emergent layer.
The forest floor is covered with leaf litter, detritus, and detritivores, such as termites, cockroaches,
and isopods. Leaves that fall on the forest floor may decompose in a few weeks rather than years,
because conditions allow for decomposers like bacteria and fungus to flourish. Nutrients are
quickly absorbed by nearby plants or washed away by frequent rains.
Courtesy of Father Alejandro Sánchez
Damp leaf litter decomposes quickly.
Courtesy of Father Alejandro Sánchez
Centipedes forage for prey on the forest floor.
The understory is a mass of vines, dwarf trees like hibiscus, and mushrooms. These producers can
survive in low light with very little air circulation. Only about 5 percent of the sunlight filters
through to the understory. Plants in the understory rely on insects for pollination. They produce
large, sweet-smelling, colorful flowers to attract pollinators. Ants, tree snails, and walkingsticks
live in the understory. Predators found in the understory include anoles, geckos, giant crab
spiders, tarantulas, and centipedes.
The larger trees making up the rain-forest canopy include Sierran palms and Pumpwood trees.
The trees have dark leaves to more efficiently absorb sunlight. Rain and moisture that falls on the
leaves drop to the forest floor. Epiphytes, like orchids and bromeliads, are plants that grow on
other plants without ever touching the ground. Red-tailed hawks and Puerto Rican screech owls
make their nests in the tall canopy trees. Endangered species, like the Puerto Rican parrot, live in
cavities of larger, older trees.
The familiar "koooooooo-keee" call of the common coqui frog can be heard throughout the
canopy, understory, and forest floor. The coqui frog is a favorite among Puerto Ricans and is
considered an unofficial national mascot. The populations of the Puerto Rican parrot and coqui
frog have drastically decreased in Puerto Rico since the 1500s.
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Courtesy of Father Alejandro Sánchez
Coqui frogs climb up into trees at night, looking for food and
mates. They jump back to the forest floor rather than climb down.
The tallest trees make up the emergent layer, which rises above the dense canopy of shorter trees.
These trees take advantage of increased air circulation and rely on wind to support pollination and
seed dispersal. Thick, waxy leaves reduce the amount of water released through transpiration in
the hot, tropical sun.
Courtesy of Father Alejandro Sánchez
Sierran palms from the forest canopy.
Courtesy of Father Alejandro Sánchez
Red-tailed hawk and chick in a nest high in the canopy.
There are more than 200 species of birds found in Puerto Rico and many more species of insects
and invertebrates. Migrating birds depend on resting in places like El Yunque as resting spots
along their long journeys.
Historical records show 22 kinds of mammals in Puerto Rico. While some still live in Puerto
Rico today, such as the Jamaican fruit bat, many of the native species have disappeared. In their
place, populations of invasive species, such as black rats and mongooses, now flourish.
El Yunque has fewer species than are found in continental tropical rain forests. Islands have a
smaller land area for organisms to use, and island populations can become isolated from
populations on the mainland. Over time these small populations adapt to their unique
environment. When populations of plants or animals are small, there is a greater chance that they
will become extinct if too much pressure is placed on the population.
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Can be duplicated for classroom or workshop use. Version date 12/2015