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Trekking the Treetops
by Terry Dunn

After months of studying tropical birds from the dark depths of the forest floor near Gamboa, Panama, my colleagues and I stumbled upon our most interesting discovery. We were searching for elusive animals and bizarre plants on infrequently used trails, but along the way we found a rickety tower of metal stairs in the middle of the forest. It was an abandoned U.S. military tower that was most likely unsafe and off-limits, but the temptation to climb it was as strong as Jack's desire to climb the beanstalk. We had watched birds from forest clearings and set up mist nets to catch the ones flying below the trees, but the treetops had been an unreachable horizon. We climbed the stairs as the tower swayed disconcertingly and we soon popped out on top of the forest canopy.

northern tamandua
Now that scientists and tourists can more easily reach the canopy, they are getting a closer look at fascinating animals such as the northern tamandua (Tamandua mexicana). (Christian Ziegler/STRI)

I can't remember how much time we sat watching the waving sea of green treetops, but my mind is permanently imprinted with the experience. It was blazing hot, windy, and full of life. Insects casually floated above the trees. The flowers of the elephant's foot tree (Jacaranda copaia) that we frequently found on the forest floor were in full glory above. At one point a mixed feeding flock of colorful birds, including green honeycreepers (Chlorophanes spiza) and blue dacnis (Dacnis cayana), landed in the tree just below us and frantically gobbled fruit before moving on. It became perfectly obvious to us that while we had been studying the birds in the understory, the real action was going on in the canopy.

The year was 1986, and only a few dozen scientists were routinely climbing up into the tropical rainforest canopy to explore a world that is sometimes said to be less known than the surface of the moon. What began as a risky, unique field of study for the adventurous few has now become the domain of many scientists, and even tourists, who use ingenious contraptions to peek at what lies above.

The Main Level
In some ways, forest canopies, whether tropical or temperate, have been as mysterious as the ocean depths were before the invention of submarines and scuba equipment. The canopy of a tropical rainforest, in particular, presents an obstacle course of challenges to curious visitors. It's not unusual to encounter stinging insects, venomous reptiles, thorny plants, razor-edged leaves, lightning, sudden winds, surprisingly cold rain, and unbearable heat, perhaps all in the same day. The hazards of temperate forest canopies may not be as abundant, but all treetop adventurers, or arbonauts, risk falling and unexpectedly finding themselves on the forest floor.

It's no mystery why scientists have been anxious to study rainforest canopies. Dark silhouettes moving from branch to branch and odd sounds emanating from the treetops have long sparked the curiosity of those watching from below. The forest canopy is a very different place from the forest floor: different climate, different species, and even different relationships between species. Scientists estimate that half of all terrestrial animals and plant species live in the forest canopies of the world. It's no wonder that Donald Perry, a pioneering canopy biologist and founder of the Rain Forest Aerial Tram in Costa Rica, calls the canopy layer the main level of the tropical rainforest.

Forest canopies may do much more than house animals and plants. According to Gary Lovett, a forest ecologist with the Institute of Ecosystem Studies in Millbrook, New York, the surface area of all the leaves and branches in the world's forest canopies is roughly equal to the surface area of the entire planet. These surfaces are a dynamic interface with the atmosphere, the place where so much of the world's gases are exchanged. How that exchange affects the world's climate remains unanswered.

Reaching for the Sky
Getting into the canopy of a tropical rainforest is not the same as climbing a backyard apple tree. Tropical tree trunks can be branch-free for the first 60 feet. Once reached, the branches are often heavily laden with epiphytes (plants that get their nutrients from the rain instead of soil), making the branches more likely to break from the extra weight of a person.

For generations, scientists attempted to overcome gravity, fear, and discomfort to get to the treetops, or resigned themselves to studying canopies from the ground. They relied on fallen branches or trees for their specimens, and occasionally cut a tree down for the sole purpose of collecting the treasures in its upper branches. They stood on nearby hilltops and watched the treetops, hoping to make sense of what they were seeing. Some even tried walking up tree trunks with spiked shoes or hammering oversized nails into the wood only to be covered with oozing sap on the descent. Steps were chopped into tree trunks, local tree climbers were hired, and in several cases, scientists used trained monkeys to scale trees and collect samples.

In the mid-1970s, a handful of scientists began using mountaineering ropes and harnesses designed to reach the canopy. Working with these tools takes a bit of practice, persistence, and not a small dose of skill and bravery. Using a crossbow, then later an invention named a mastercaster, an arrow attached to weighted fishing line is sent up to a promising canopy branch—a task that can take many hours of shooting, then untangling and shooting again. Once the fishing line is placed, parachute cord is usually attached to the fishing line and drawn over the branch. Finally, a climbing rope is drawn over the branch in the same way. When the rope is ready, the climber puts on harnesses and attaches ascenders, then shifts his weight between leg slings and a waist harness while sliding the top and bottom ascenders. Eventually the climber inchworms to the top.

In the late 1970s, when Donald Perry was routinely climbing trees in Costa Rica, he built a platform in the canopy, complete with a cot and other comforts of home. Of course, "home" usually doesn't include biting insects, curious mammals, and vicious storms, but his platform enabled him to observe the doings of the local canopy dwellers day and night for an extended period of time. Perry would go on to develop a system of steel cables that allowed scientists to propel themselves in a radio-controlled chairlift through the canopy.

Smithsonian canopy crane
The Smithsonian's canopy crane in Panama City reaches over the treetops. (Marcos Guerra/STRI)

Another leap in canopy access came unexpectedly during a scientific meeting in Miami. As the story goes, Alan Smith, the late Assistant Director for Terrestrial Research at the Smithsonian Tropical Research Institute, was taking a lunchtime walk. He reflected on a common theme at the meeting: Scientists were frustrated that they had to wait for information to fall from the trees. (Not all scientists have the athletic ability or the fearlessness to use the rope-climbing techniques.) While pondering this predicament, Smith noticed a construction crane and had a proverbial lightbulb-over-the-head moment. He persuaded the Smithsonian Tropical Research Institute to rent a construction crane and erect it in a large forest in Panama City, Panama. A live webcam at link towww.stri.org now gives web surfers a view from the crane.

The crane was good at getting scientists to the tips of branches, an area that is difficult to reach by climbing. So much information was gathered from the crane in Panama that other countries were inspired to erect their own. There are now canopy cranes in forests in Venezuela, Malaysia, Australia, Germany, Switzerland, Japan, and the United States.

Several years ago I took a deep breath and stepped out onto another advance in canopy access: canopy walkways. One of the largest networks of canopy walkways and towers was located at the Amazon Center for Environmental Education and Research (ACEER) in Peru, 100 miles by boat from the nearest frontier town. The suspended walkways, made of linked aluminum ladders covered with wooden planks for floors and rope nets for sides, bounced and swayed with even the most hesitant footsteps. Each span was higher than the last and ultimately visitors arrived at a 118-foot-high vista overlooking an endless blanket of green treetops. On the ascent and descent, it was dramatically clear how the forest changes with height, providing visitors with an exceptional perspective of the forest and scientists with easy access to a large area of the canopy. ACEER has since turned the walkway over to a privately owned ecotourism company, but it plans to build an even longer canopy walkway in the Amazonian cloud forest of the Andes.

Another method of getting up into tropical rainforest canopies is by using an inflatable raft that rests on the top of the rainforest canopy. The structural support comes from a hexagonal, inflatable frame that has a base of woven netting. Five scientists at a time can walk around on this uneven, 4,844-square-foot floating surface to conduct research. The raft, and sometimes the scientists, is delivered to the treetops by a dirigible, making it easy to change study locations.

The latest development in canopy access eliminates the need to combat the elements and a fear of heights while gathering data. Electrical engineers at the University of California, Los Angeles, have created a canopy robot that runs along a cable through the top branches at the Wind River Canopy Crane Research Facility in Washington State. The small robot is tethered to a solar cell and battery pack, and has a camera, processor, sensors, and a handy wireless link to the Internet. It can move horizontally and vertically to sample temperature, humidity, and sunlight along its route. In the future, scientists hope the canopy robot will help keep track of carbon dioxide and the growth of leaves and branches, and they may add more robotic siblings to the Washington site.

The Research
The explosion of canopy access techniques has spawned an equally large burst of research. In 1970, there were practically no published research articles about forest canopies. In 1980, there were about 20 articles and the number more than quadrupled over the next decade. Now, "the field of canopy studies is beginning to coalesce," according to Nalini Nadkarni, a professor at Evergreen State College in Olympia, Washington, and president of the International Canopy Network. "What was wrong with forest ecology 25 years ago was that the canopy was not considered," says Nadkarni. "There is now an integration with general forest ecology."

The news from the world's canopies is changing how scientists view forests. "Although the canopy is a short distance from the forest floor, it constitutes many, many microhabitats and microclimates," states Nadkarni. The forest floor is fairly consistent by comparison.

Photosynthesis in canopy plants can be very different than in plants down below. In Costa Rica, scientists have found that epiphytes are affected by air pollution sooner than the rooted plants on the forest floor. While climbing a tree in Olympic National Park, Nadkarni discovered that big-leaf maples actually sprout roots from their branches in order to get the nutrients that accumulate under the mossy mats on the branches.

Smithsonian scientists
Smithsonian scientists are carried above the canopy in a box attached to the STRI canopy crane. (Marcos Guerra/STRI)

The Smithsonian Tropical Research Institute now operates two canopy cranes in Panama and scientists are using them to study a variety of topics including gas exchange between the canopy and the atmosphere, treetop pollination, and insect species diversity. Among the new findings, scientists have discovered that vines are dominant plants in the canopy in terms of biomass. They compete with host trees for light, often shading out canopy leaves. One scientist also found that a common fig tree species had the highest photosynthetic rate ever recorded in the wild.

Studies show that forest canopies play a significant role in the world's climate regulation and filter out air pollution. Some scientists suggest that forest and scrub areas in the continental United States may breathe in a third of the carbon emissions (half a billion tons) spewed out by our cars and factories each year. Now they hope to find out if the forest can keep soaking up the massive amounts of carbon we are producing.

Animal research in the canopy has been equally revealing. Animal species that are considered rare near the forest floor, such as southern flying squirrels (Glaucomys volans) in the temperate forests of western Massachusetts, are sometimes abundant in the canopy. New species have been discovered, such as the furtive spiny tree rat (Mesomys occultus) in the Brazilian Amazon; a poisonous caterpillar in Peru; and more than 300 new species of beetles, spiders, flies, and wasps in just five old-growth trees on Vancouver Island, Canada.

Terry Erwin, a senior scientist and curator at the Smithsonian Institution, has collected an astounding amount of data on insect biodiversity in forest canopies using a technique called fogging. In 1974, he sprayed a fog of biodegradable insecticide into 19 trees in Panama to collect specimens. That study was so successful that he continues to use the fogging technique, and to date he has amassed more than 20 million arthropod specimens for the National Museum of Natural History. He once found 1,700 species of insects in just one Peruvian tree.

Just as new technologies have helped scientists get into the canopy, new technologies are being used to study them. To get a handle on insect biodiversity in forests, scientists are taking bio-acoustic measurements of insect sounds and analyzing them with computers.

Roman Dial, a professor at Alaska Pacific University, is using a laser range finder to determine the volume of the airspace in canopies and the abundance of canopy objects, like foliage, limbs, and trunks. Airspace is important for air movement in the canopy and for gliding vertebrates such as the Malayan flying lemur (Cynocephalus variegatus) and the paradise tree snake (Chrysopelea paradisi) in Borneo. While hanging from a rope, Dial takes measurements, then downloads the information into a Palm Pilot for analysis later in the lab. He is already finding that the density of foliage is tied to the abundance of different animal groups.

Mist nets, similar to the ones I used on the forest floor nearly two decades ago, are now being strung in tropical rainforest canopies to get an idea of how different species of birds spread themselves out in the layers of the forest.

Canopy Access for the Masses
As scientists continue to expand their range in the canopy, governments, organizations, and tour operators are beginning to see the potential for getting tourists into the canopy. On five continents, people can now ascend into and above the trees. There are at least 17 canopy walkways used for tourism or education worldwide. Towers and platforms rise from forests in Peru, Florida, and Malaysia, and aerial trams glide through several forests in Central America. Most of the facilities have been built to give regular people a chance to see the wonders of the canopy, sometimes in combination with ongoing research.

Some facilities are also appealing to Tarzan wannabes. In Costa Rica, a daring person can go to Sky Trek in the cloud forests of Monteverde to walk on six suspension bridges (one of them almost 1,000 feet long), two canopy towers, and 22 platforms connected by eleven zip lines—steel cables up to 525 feet off the ground that hook to visitors' harnesses so they can zoom from tree to tree hanging high above the forest. It's questionable how much a person can appreciate the forest canopy when they are whizzing through it, however, and there is a growing debate about the role of canopy access for tourists.

Canopy walkways, aerial trams, and canopy towers can affect the trees they come in contact with and local animals are exposed to visitors daily. Zip lines require constriction bands to be tightly wrapped around a tree. With rope-climbing, epiphytes are knocked from branches, bark is scarred, and animals are disturbed. Nadkarni says she has come to peace with the minimal damage that comes from tree climbing for research purposes, but is concerned about the safety issues that have arisen when people climb trees to stage environmental protests. Along with rejecting authority and breaking into protected areas, there seems to be less attention to safety. "Accidents put a damper on the whole field," Nadkarni observes.

In addition to tree damage, canopy access for tourists can cause other problems. According to José Courrau, former assistant superintendent of Braulio Carrillo National Park in Costa Rica and now an independent consultant in ecotourism planning, "when not properly supervised, canopy exploration allows tourists access to resources (orchids, frogs, flowers) that could be illegally extracted or damaged." Well-meaning tourists can also harass wildlife. "During my last visit to Monteverde's Sky Walk," says Courrau, "I saw tourists frantically following a female quetzal along a walkway for pictures during the dry season, which is nesting season for the quetzal."

Canopy tourism does have a positive financial impact on local economies, especially in developing countries. When tourists come to see an intact forest, there is less incentive for local people to cut down the forest for other purposes. Since its inception, more than 10,000 visitors experienced the ACEER Canopy Walkway, each one a paying customer.

Of all the canopy access methods, canopy walkways seem to be the favored method of getting tourists into the canopy. People slow down to absorb the experience, the walkways can handle large numbers of people, and the walkways protect the forest floor from erosion and compaction that occurs on traditional forest trails. When done well, walkways can be a wonderful educational opportunity. "There is something about seeing the forest from the canopy," explains Nadkarni. "Something clicks. There is something that really happens." That "something" has an influence on whether forests, and the animals that live in them, will be valued and conserved.

I doubt the rickety canopy tower I found in the forests of Panama is still standing. A strong wind or the military most likely took it down. I did get the chance to return to my Panamanian study area late in 2003, and, like many places, the lure of the canopy has attracted the masses. On one end of Gamboa, the tiny town where I used to live, a short aerial tram lifts visitors to a spectacular canopy tower. Both the tram and the tower are wheelchair accessible. The tram slowly ascends a hillside, but barely gets above the canopy. The tower, on the other hand, literally towers above the canopy. It provides views of the Panama Canal, the Chagres River, Gamboa, and, most impressively, miles and miles of rainforest treetops. Small birds alight on the branches and flocks of parrots can be seen flying at eye level in the distance.

Thankfully, the forest and its inhabitants haven't changed much. Now, thousands of people can see this fascinating ecosystem from the tops of the trees, and explore a whole new world right here on Earth.

—Terry Dunn is a freelance writer living near Sandia Mountain in Albuquerque, New Mexico. She wrote about wildlife forensics in the November/December 2003 issue of ZooGoer.

ZooGoer 33(5) 2004. Copyright 2004 Friends of the National Zoo.
All rights reserved.

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