by Suzanna Engman
photos by Jerry Bauer

Rising 3500 feet into the trade winds over eastern Puerto Rico is a basaltic mountain whose orographic [relating to mountains] effects produce regular rains and cause a lush tropical forest to drape deeply dissected ridges and river ravines with a rich green carpet. Because the Spanish Crown passed ownership of the upper altitudes of this mountain to the U.S. Forest Service, the Luquillo Experimental Forest, as it is now called, has remained continuously in forest cover. In Spanish times, the largest of the virgin forest trees on the lower slopes were pulled down the mountain by oxen a few at a time to build and provide furniture for San Juan, but the forest as a whole survived.---Howard T. Odum, A Tropical Rain Forest, 1970.

The Luquillo Forest may well be the most studied of all neotropical, or new world tropical, rain forests. During the last fifty years, scientists from the University of Puerto Rico, Río Piedras campus and around the world have surveyed, recorded the elevation, mapped, and divided the land into quadrants. They have chemically analyzed the soil to determine carbon and nitrogen levels; measured trees for growth and age (rainforest tree trunks do not have the frost-induced easily discernible rings that indicate the age of trees in temperate forests); taxonomized the flora and fauna; recorded and charted the rainfall; examined steams and rivers for microorganisms; observed the regeneration of forest ecosystems after hurricanes; and monitored endangered rain forest species such as the Puerto Rican parrot (Amazona vittata vittata).

Yet, despite the hurricanes that regularly disturb the rain forest and the research that at times has defoliated it, the Luquillo Forest, also known as El Yunque, thrives today. “It’s a well-known ecological site, internationally and locally. To the locals the Luquillo Forest is an icon for conservation,” says Elvia Meléndez-Ackerman, Ph.D., Director of the Institute for Tropical Ecosystems Studies (ITES), which celebrates its 50-year anniversary in November.

As a national monument the forest is protected from development but is not immune to surrounding development. Today, the biggest challenge to forest managers is rapid urbanization and the accompanying rise in the demand for water. “We do have a good grasp on how this forest works. I think that puts us in a good position to monitor and understand the effect of the tremendous population growth on the eastern side of the island. Knowing what we know about the effect of urbanization on water supply and increases in environmental temperature, there’s concern that increasing urbanization around the forest may affect the water service. The good thing Luquillo has going for it is that we know so much about it. The bad thing is that what’s happening around it is happening so fast,” says Meléndez-Ackerman. The long-term observation and data collection in the Luquillo Forest has enabled researchers to understand the intricate web of interrelationships and the resilience of rain forest ecosystems. In the first stages of rain forest research, scientists observed and monitored to answer the question, what if? What if the rain forest were irradiated with gamma rays? What if herbicides defoliated the forest? What if a hurricane hit the rain forest? What would happen?

“Now we know what will happen, if. In the process we have managed to gain a great understanding of how this forest ecosystem functions, enough to know that human-mediated changes around the Luquillo Forest as well those as occurring at a global scale, such as climate change, may threaten its balance. The emphasis is now on predicting the ecosystem’s response to these changes as well as monitoring the changes. You have to do things in parallel because you have these threats that can be so immediate—what humans are doing to this forest is happening at a very fast rate—and perhaps if we only focus on monitoring changes it might be too late. We have all this information, and we need to get it to the people and explain what it means.”

The Rain Forest Project

The Institute for Tropical Ecosystem Studies can trace its roots to the Atomic Energy Commission (AEC), created after World War II to control U.S. atomic energy, produce fissionable materials, manufacture and test nuclear weapons, and develop nuclear reactors. The AEC also promoted peaceful uses of atomic energy, for example, the production of electricity. In 1955, the AEC included ecological systems in its biological and medical research program. Its mission, wrote John N. Wolfe, was “to anticipate the manipulations resulting from man’s needs, follies, wants, and dreams which will affect the environments of the planet.”

“ITES was created from the Terrestrial Ecology Division of the Center for Energy and Environmental Research, which was originally the Puerto Rico Nuclear Center (PRNC),” says former Director of ITES and Senior Scientist of the Terrestrial Ecology Division, Bob Waide, Ph.D. “The PRNC was founded in 1957 by the Atomic Energy Commission, essentially, to provide technical transfer in atomic energy to Latin American nations and to work in Puerto Rico to determine whether atomic energy could be a viable energy alternative.”

Director of the International Institute of Tropical Forestry (IITF) in Puerto, Rico Ariel Lugo, Ph.D., recounts why Puerto Rico was chosen as a place to build a nuclear center and why the PRNC chose to experiment on the rain forest: “Nuclear energy had become a priority and the government sent a whole bunch of bright young people to get degrees in radiation and atomic energy because they had the notion that they would establish nuclear plants on the island. The PRNC started all this. Puerto Rico was a high-tech place, even then. The United States government was considering using atomic energy to explode a new canal route near the Panama Canal, so the AEC started commissioning ecological research. They wanted to know how resistant ecosystems would be if they were irradiated.

“There were irradiation experiments in Georgia, South Carolina, Tennessee and New York. The government was irradiating different kinds of ecosystems. And they said well, how about the tropics? The AEC could have gone to Central America, but they came here because Puerto Rico had the PRNC, and the Forest Service agreed to allow the University of Puerto Rico to use the 180 acres where the irradiation experiment was conducted.”

The AEC’s first and biggest project in Puerto Rico, The Rain Forest Project, 1963-1967, irradiated the rain forest with gamma rays to study their effect on rain forest ecosystems. Scientists had discovered that pine trees are highly sensitive to gamma and neutron radiation, disproving the myth that plants are radiation resistant. They wanted to find out what would happen to a rain forest exposed to gamma radiation. “Now people criticize how El Yunque was irradiated, but they don’t realize that, at the time, this was a matter of national importance,” says Lugo.

Fifty years prior to the project, the Luquillo Experimental Forest had been set aside as national forest land, and the researchers from the IITF, a division of the Forest Service, began to study it intensely. Noted ecologist Howard T. Odum, PhD came to Puerto Rico to design and implement the Rain Forest Project. Lugo was his student and assistant. “The whole project was incredibly ahead of its time, in terms of a big experiment with a control site and a cut site. He had a radiation area, an area of no radiation, and an area of cut rain forest. The idea was to isolate how the rain forest would react to radiation and how it differed from being cut,” says Lugo.

In 1963 scientists started to gather in Puerto Rico to prepare for the experiment and to fence off the 180-acre area from the public. Two sites were surveyed for the project, one for the experiment and the other as a control site. In addition, another control site was cleared of all vegetation. On January 19, 1965 experimenters uncovered the 10,000-curie cesium source placed at the center of the test area. After three weeks of irradiation, the forest showed no signs of stress. The irradiation continued for three months, and trees and vegetation started to die. Within a year, the ground was defoliated. Leaves fell from trees, and defoliation continued to spread for almost two years.

“People didn’t really understand radiation very well back then,” says Waide. “They didn’t know what the effects would be. They did a whole series of experiments around the country to try to understand the effects of principally peaceful uses of radiation. One of the interesting things that came out of the Rain Forest Project was that you could actually see in El Yunque the same types of isotopes that were being generated by the atomic bomb testing. The elfin forest up here was filtering them right out of the clouds. That was a very interesting result, and it focused people on the idea that there was a lot of connectedness that we weren’t really aware of.”

The amount of radiation that will produce one unit of ions per cubic centimeter is measured in Roentgens. It soon became apparent that rain forest trees were significantly more resistant to radiation than trees from a temperate forest. “There’s a tree there that took 50,000 Roentgens and lived. This particular tree was burned on one half but the other half was perfectly ok,” says Lugo. “To put the experiment into perspective, if you go to the doctor and get an X-ray you get one Roentgen. If you get 500 X-rays, you would probably die because the human being can only take 500 Roentgens. It turns out that the southern pines are similar to humans in terms of their resistance to radiation because they also can only take 500 Roentgens. We had rain forest trees taking 50,000.” Still, all the trees within 0-30 meters of the source died within a couple of years.

The irradiated forest was studied for 23 years, until 1988. At that time it had not fully recovered, as evidenced by a noticeable light gap in the canopy. Regeneration was slower in the irradiated forest than in the cut control forest, and the effects of radiation were apparent in plant tumors, “two-headed” palms with dichotomous apical meristems, and trees that were dead on the side facing the radiation source but growing and reproducing on the sides protected from the radiation.

Ariel Lugo

Today to the untrained observer, the Luquillo Forest test site is indistinguishable from the rest of the rain forest. The huge tree that survived the 50,000 Roentgens it was exposed to has since died, a victim Hurricane Hugo in 1987, but its decomposing trunk, surrounded by lush vegetation, still remains as a reminder of the experiment, the resistance of rain forest trees, and the resilience of ecosystems.

Hurricanes and the Rain Forests

Many of the rain forest studies have focused on how the ecosystem regenerates itself after disturbances, for example after a devastating hurricane. Waide, now Executive Director for the NSF sponsored Long-Term Ecological Research (LTER) Network Office, describes research designed to answer this question. “Our plan in 1989 for LTER had been that we would establish a baseline of data and eventually a hurricane would come along. Well, a hurricane came along earlier than we expected. Our original thoughts had been to perform some manipulative experiments, but we didn’t need to do that because we already had the biggest experiment that we were ever going to have.”

Hugo was a category 3 hurricane when it struck Puerto Rico in September 1989, causing $13.6 billion in damages and making it at the time the most damaging hurricane on record. Puerto Rico was particularly hard hit, especially in the eastern part of the island, where the Luquillo Forest is located.

Waide recalls that the scientists had to rethink their research strategy. “The next day we got to the town of El Verde, which is about three or four kilometers from the field station, and the road was blocked at that point. So we had to walk up from there. The driveway had something like thirty or forty trees across it. The extent of damage changed our mindset about the way we thought that the forest was operated.” The scientists soon set up a long-term monitoring program.

“I wouldn’t call a hurricane a disaster. It’s a human disaster but it’s a natural disturbance because the forest, we calculated, has been subject from 500,000 to a million hurricanes since Puerto Rico was formed about 30 million years ago. It has gone through this a lot. The forests and the ecosystems up there are, if you will, used to it. They’ve adapted to it. The organisms have adapted to it. It’s impressive to us because we maybe see only one in our lifetime, but the forests have seen a lot of this.”

The question of post-hurricane regeneration soon branched out to questions about rain forest adaptation. According to IITF director Lugo, “If the biota and organisms in Puerto Rico were not adapted to hurricanes, they wouldn’t have survived. You have to have hurricane adaptation. If you don’t, you die.”

Tropical rain forest trees developed several adaptive strategies. “First of all you grow like hell between hurricanes. Secondly, you need to have a way of either dropping your leaves when the wind hits, and some trees do that, or you need to have resistant wood. And you need to have a mechanism for resprouting fast after the hurricane because you are going to have a lot of competition afterwards to maintain your position in the forest—because the way trees win is by shading everybody out,” says Lugo. Another mechanism is the capacity to reflower and reproduce quickly. Trees in Puerto Rico start reproducing very quickly. They don’t wait to reproduce until they are 70 or 80 years old. All these things accelerate regeneration.

“The trade winds and the hurricanes keep the forest trim, and you don’t have the big trees sticking out because if you stick out, you do battle with the wind. Now if you go to South America where there are no hurricanes, and you climb any tower, you have what they call the emergent trees. You have big ones that stick out 20 meters above everybody else, and spread out above. You don’t have those here because they would fall over when the winds came. How the forest is structured is determined by the hurricane.”

One of the great paradoxes is that trees more exposed to hurricane winds fare better than those that are more protected. “Frank Wadsworth [former director of IITF] noticed that the biggest trees in Puerto Rico were on the ridges and wondered why. That’s where the wind is strongest, so he reasoned that they were there because the roots were holding them to the rocks. We made two discoveries recently that show that that’s not the complete story. We found out that the ridge is the only place in El Yunque where it doesn’t flood. The rains are so heavy and the clays are such that everywhere else water accumulates and there is no oxygen for the roots, which weakens the trees.

“But a more important discovery was made by a student from Nepal who came over to do field work for his dissertation. He started poking around all the tabonuco trees on the ridge with an aluminum rod to map the root system to see whether the tree roots were wrapped around rocks. What he found, to our amazement, is that the trees were grafted together. They unionized. It’s cooperation. There are 30 or 40 or 50 trees all hanging together by the roots. They’re not clones. They germinate and then they connect. And they strengthen the connection, so when the hurricane comes, the whole group is as steady as a rock.”

Within a group of unionized tabonucos, the scientists observed that there was always one tree that was taller than others. “One of the big mysteries was how the smaller trees survived in the shade of a big tree. When you measure how much food they make and how much food they’re consuming, you find they’re consuming more than they’re making. How did they survive? The big tree feeds all the others, keeping the clan together. When a hurricane comes the trees drop their branches. But because they’re interfed, they can resprout like mad after a hurricane. There’s always a mother tree. And no other species can be there. They control the area of best irradiation, where there’s more soil and better conditions.”

Future Research in the Luquillo Mountains

Climate change and an emphasis on predictive and preventative measures to avoid ecosystem damage drive the current research in the Luquillo Forest, and many studies are focusing on water dynamics and atmospheric science, notes Mélendez-Ackerman. “A lot of the water that comes through Luquillo comes from precipitation from cloud formation. It’s possible that urbanization will affect cloud formation, and we’ll end up with less rain. Put on top of that global climate change and the related impacts of the local climate in the Caribbean. The effects from these are escalating.

“We’re in a position to model what would happen if we take more water for human cnsumption. We’re in a position to start moving into a prediction phase. There are still things not understood—subjects related to atmospheric sciences, for example. One of the things that ITES would like to do is strengthen its capacity in the area of atmospheric science and use the Luquillo Forest to do that kind of work.”

The Luquillo Mountains are in a unique geographic position within the Caribbean to attract more scientists and funding. As a territory of the United States, development of atmospheric science infrastructure in Puerto Rico would eliminate the difficulties of setting up complicated monitoring devices in a foreign country. The elevation gradient and proximity to UPR, RP’s research facilities also make the site attractive. “You have cloud formation in a gradient that you can access. There are a number of atmospheric science researchers who have looked at Puerto Rico as a site for developing this kind of research. There are studies that show changes in Sahara dust patterns in the Caribbean, with Puerto Rico in the direct path,” says Meléndez-Ackerman. “We also receive the effects of Montserrat events every so often, and the Luquillo Mountains are in a great position to be monitored for these events. We can even monitor what seems to be pollution influxes from the eastern side of the United States by studying the wind currents and how they relate to changes in the particle content of the air. We would like to encourage this type of research and perhaps develop the necessary infrastructure that is needed to address more complex questions in the Luquillo Mountains.”

Other Areas for Ecological Research in Puerto Rico

Climate change could also initiate expansion of ecological research in Guánica, on the west side of the island. A proposal is being considered for funding from the National Science Foundation’s National Ecological Observatory Network (NEON) that would enable scientists to study environmental challenges in order to achieve credible ecological forecasting and prediction. Guánica State Forest is affected by fluctuations in the Trade Winds, the North Atlantic Oscillation, flow of transequatorial air masses from the South Atlantic and El Niño events, so ecosystems are expected to be highly sensitive to climate change.

“Never before has the NSF invested big money in ecology. They have invested in oceanography, medicine, physics, and astronomy. Never in ecology. NEON will lift LTER a notch with high tech technology,” says Lugo, Co-Principal Investigator of the proposal. Scientists and engineers in Puerto Rico could soon be linked via state-of-the-art communications. NEON supports cutting-edge lab and field instrumentation; site-based experimental infrastructure; natural history archive facilities; and computational, analytical, and modeling capabilities.

Data from NEON studies are intended to be made available to the public and for educational purposes, especially for experiential learning and biosphere literacy. Its research and communication infrastructure goals include public dialogue and education of policy and management decision makers. It aims to link education and social science research with ecologists and biologists.

“You have to understand how the current success of ecological science in Puerto Rico is the result of people like Odum. That rain forest book is like The Bible,” says Lugo. “At one time I felt like there was nothing left to do—Odum already did it all. Now I realize, my God, there is still a lot to do.”