October 2000
Suspension bridge walkway through the canopy at Myakka River State Park, Florida. The bridge, made entirely of wood, is 85 feet long and 25 feet high. Photo: Oksana Hlodan.
Alexander F. Skutch, in his A Naturalist in Costa Rica (1971), encouraged his readers, writing, “To know the forest, we must study it in all aspects, as birds soaring above its roof, as earth-bound bipeds creeping slowly over its roots.” Until recently, our perspective on forest ecology was ground-based and clueless about canopy processes. Only during the past 15 years has our understanding of treetop ecology expanded substantially beyond this bipedal bias — in large part because of the dauntless efforts of a handful of temperate and tropical biologists working from ropes, walkways, airships, cranes, and towers sometimes 120 feet off the forest floor.1 That’s the height of a 12-story building!
Wonders of the forest canopy
Why study the forest canopy ecosystem?
- It is the layer containing most of the productive tissue for the entire forest. Simply put, it is a gigantic food factory elevated on living stilts.
- Consequently, the forest canopy is also where most of the world’s estimated 30 million species live, munching away at all those leafy sugars.
- It is a living aerial laboratory for discovery and opportunity.
- It is an unexplored frontier for scientific research and education.
The metaphors in the scientific literature for the forest canopy are resplendent and atypically poetic, capturing some of our childlike intrigue with this borderland of science.
- Canopies are described as tropical air castles, canopy oceans, hanging gardens, green mansions, aerial continents, highways in the trees.
- Up there, we are explorers in the roof of the world’s forests. Until we can quantify, replicate, observe, and collect in this leafy realm, we wax romantic, unsure about the outcomes of our inquiry but convinced of its merits.
- Often quoted in recent canopy texts is an observation from William Beebe’s Tropical Wild Life in British Guiana (1917): “Yet another continent of life remains to be discovered, not upon the earth, but one or two hundred feet above it, extending over thousands of square miles … There awaits a rich harvest for the naturalist who overcomes the obstacles — gravitation, ants, thorns, rotten trunks — and mounts to the summits of the … trees.”
A rallying cry for canopy scientists, Beebe’s prose compresses all the reasons for canopy research into a single poignant word, discovery. The word registers on the heart strings of every biologist, teacher, and student lucky enough to enter the forest canopy. The canopy is a New World for us or, more accurately, an Old World that our remote ancestors left behind millions of years ago. It is a siren song for our genetic memory.
A new look at canopy ecology
The 1990s represented the defining decade for the emerging science of canopy ecology. Access methodologies, field protocols, scores of articles, several textbooks, two international symposia, and an Emmy-winning film (National Geographic’s “Heroes of the High Frontier”) were among our successes. In addition to single-rope technique (SRT), there are other ways to get to the canopy, including airships, treetops rafts, sleds, canopy cranes, towers, tram-lines, and walkways that now number about 100 sites worldwide.
Just in the eastern United States alone, eight forest canopy walkways and platforms are in place for research and education: Hopkins Forest, Williams College, Williamstown, MA (1991); Hampshire College, Amherst, MA (1992); Coweeta Hydrological Laboratory, NC (1993); Selby Botanical Gardens, Sarasota, FL (1994); Millbrook School, Millbrook, NY(1995); Burgundy Center for Wildlife Studies, Capon Bridge, WV (In preparation); EcoTarium, Worcester, MA (1999); and Myakka River State Park, Sarasota, FL (2000). The last two provide access to the public.
What have we learned from all this lofty activity?
First, an aerial view reinforces the idea that forests are complex systems of interrelationships. And that presents to us a new, more comprehensive definition of the term, canopy.
- It once referred to the uppermost layer of vegetation in forests. Now the botanical term refers to all above-ground vegetation in a plant community. According to scientists in the field, each plant community has a canopy.
- Each tree has a canopy.
- A temperate or tropical forest has a canopy. Technically speaking, even an orchard, a lawn, a golf course, and a kelp forest have canopies. This systems-wide term includes plants and all their above-ground associations.
- The term, canopy, refers not only to the architecture of the community but also to species composition, nutrient cycling, energy transfer, plant-animal interactions, and conservation issues.
Second, our work in the canopy has revealed to us that more than 30 million species of organisms inhabit the planet — plants, animals, bacteria, fungi, and protists.
- More than half are thought to be residents of tropical rainforests, and most of these species reside in the forest canopy.
Collectively, these treetop organisms provide many of the ecosystem services, economic benefits, and aesthetic and ethical aspects that make the rich tapestry of tropical rainforests vital to the planet’s functioning.
Scrubbing carbon dioxide from the atmosphere, supplying medicines and foods, providing living laboratories for scientists and students, and representing an irreplaceable home for a plethora of life — these are just parts of the wonder found in the tropical rainforest canopy.
Now many of the canopy biologists who were trained in the Northern Hemisphere but worked side-by-side for years with their equatorial colleagues have returned to their own temperate forests to investigate the biodiversity and ecological processes at work in these northern plant communities.
Our third lesson from the canopy is a sad one. Deforestation, one of a number of human-accelerated changes across the planet, now threatens the biological integrity of forest systems.
The collective fallout from these changes may even rival that of previous major episodes of extinction on Earth. Like the 65-million-year-old Cretaceous/Tertiary mass extinction, humans are now unwittingly fraying the interconnecting threads of life’s tapestry. The third lesson? Unless we can halt human-accelerated changes such as deforestation in the next decade or two, we may be haunted by their ecological repercussions. The window of opportunity will have closed tightly and indefinitely.
Let’s not forget the wrenching lessons of Rapa Nui, also called Easter Island, where its entire human population disappeared after the island ecosystem’s natural resources were irreparably exploited.
Tropical forests are disappearing at a rate of approximately 100 acres per minute worldwide. Relatedly, species that depend upon them are also vanishing. Pulitzer-prize-winning E.O. Wilson and others estimate that the background rate of extinction is one to three species per year.2
In the 1970s, that rate accelerated to one species per day. Then, in the 1980s, the extinction rate climbed to one species per hour. In the first few decades of the 21st century, we may see 100 species or more per day fall prey to human ignorance and appetites. The implications for the tapestry of life upon which we depend are horrifying.
Protecting the canopy
Yet the picture is not completely dark. Professional conservationists, science educators, volunteer networks, religious leaders, and others are calling for responsible stewardship of our natural resources. Canopy ecology is an emerging science that has helped us clarify our needs and directions. Thomas E. Lovejoy, renowned tropical ecologist and author at the Smithsonian Institution and World Bank, recently wrote: “There is no better evidence than canopy biology that the age of exploration is not over.” There is no better reason than canopy biology to foster a collaborative effort among scientific researchers, educators, and all other components of society. There is no better reason to invite students young and old to enter the treetops. A New World exists, accessible by ropes and climbing gear, airships and canopy bridges in a borderland of science. Each of us is a Columbus, a Jacques Cousteau, a William Beebe suspended in a vertical moment of discovery. What better ingredients could we have for learning about a global treasure that needs all our collective energies and enthusiasm to survive?
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