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It's a Jungle Up There

YALE UNIVERSITY PRESS

Chapter One

Indeed over all the glory there will be a canopy. It will serve as a pavilion, a shade by day from the heat, and a refuge and a shelter from the storm and rain. -Isaiah 4:5-6

When my children were toddlers, we passed many hours on our sheep and cattle ranch in rural Australia watching the livestock seek shade. They squeezed together under the few remaining gum trees in the midst of our sun-baked, wind-swept paddocks. If you were a dingo searching for dinner, it would be easy to head for one of the few shade-giving trees under which stood a smorgasbord of lamb chops and steaks. The canopy was not only important to animals that benefited from its shade, but also critical as a home to the many other organisms that made up the forest ecosystem. We would catch Christmas beetles, count caterpillars, track down goannas (Australian lizards), observe koalas, and monitor magpie nests.

In the past decade, tree canopies have attracted intense attention in urban centers, not just in forests. Like livestock inthe outback, humans have discovered that shade enhances the quality of life. Shade provides recreation: we read, garden, picnic, swim, party, dine, and seek romance in shady places. Shade enhances our economy: we save money on air-conditioning, building maintenance, paint, cars, and even heating by creating canopy cover in our neighborhoods. In our typical headlong impatience to sanitize and modernize our cities, we tend to cut down trees without understanding their importance. In Florida, where development is epidemic, builders often clear all trees, including mature, hard-to-replace live oaks, before building homes. Then the new owners struggle for many years to restore a shady canopy around their house. Despite our increased knowledge of the benefits of tree canopies, we still follow this shortsighted, "cut-it-down" attitude toward our forests. Why are tree canopies so underappreciated and understudied, yet so essential to life?

Almost thirty-five years ago, when I was in tenth grade, the first Earth Day was celebrated. Almost thirty years ago, when I was in college focusing on environmental studies, I clapped with joy when the Endangered Species Act was legislated. Yet since then, an estimated 800 million or more acres of tropical rain forest have disappeared. Other ecosystems too are disappearing-the Florida coastline, North American old-growth forests, wetlands, and coral reefs.

I cared passionately about this vanishing natural world, enough to pursue it as a vocation. In 1978, while a graduate student living in Australia, I started climbing rain-forest trees because I was curious about what lived at the top. I asked questions: How long did evergreen tropical leaves live? Why didn't insects eat up all that green, which they obviously found so delicious? How did that green material manage to fuel all the food chains on earth? How did foliage defend itself from predators, since plants cannot run away from their enemies? This was my world.

Almost every child climbs trees, and I had figured out how to continue this wonderful pursuit as an adult. I frolicked in the forest and became an expert on forest canopies. I never envisioned, however, that my world of the treetops would become critical to the future health of our planet. But one of my colleagues turned the world of canopy biology upside down.

Quite by chance, Terry Erwin of the Smithsonian Institution discovered such abundance of life in the treetops that forest canopies became a hot spot, or epicenter, of field research. Terry sprayed several canopies in the tropics with a mild insecticide (a procedure known as fogging), and all of the arthropods fell to the ground in a heap. He could then count and catalogue the insect residents of an entire tree. From that initial harvest of insects in Panamanian rain-forest trees, he calculated that there might be 30 million species on our planet, not 3-5 million as previously estimated. As one of a handful of scientists studying the treetops in the early 1980s, I suddenly found myself in the spotlight, along with Erwin and several other canopy biologists.

Why was Terry's discovery so astounding? As field biologists who focus on species diversity, we seek to catalog, identify, and understand the role of all creatures. It is not simply a naming game; the ultimate purpose is to understand the structure and function of an ecosystem, even as we seek to know how the components of a car engine operate to create an efficient machine.

Our challenge of discovering and identifying the organisms on the planet is not easy. Finding a new orchid in the treetops is 90 percent perspiration and 10 percent luck. All of these organisms-orchids, beetles, birds, vines-are part of what we call biodiversity, otherwise known as the variety of species on Earth. Over the past two decades, the term "biodiversity" has become politically and scientifically important, as human activities have accelerated ecosystem degradation and subsequent loss of species throughout the world. Our new awareness of the complexity of ecosystems suggests that disruption of their function will be extremely difficult, perhaps impossible, to repair.

In the 1800s, at the dawn of modern biodiversity, Charles Darwin estimated that approximately eight hundred thousand species inhabited the Earth. (I can only imagine that the Queen of England was most impressed by his scientific prowess in calculating this apparently enormous number.) Nearly one hundred years later, however, Terry Erwin's collections from canopy fogging raised Darwin's tally more than fortyfold. Similar data sets all over the world, including those of Nigel Stork in Malaysia, Yves Basset in New Guinea, Joachim Adis in Brazil, and my own work with Roger Kitching in Australia, have confirmed Terry's initial figures. We now believe that the treetops are home to perhaps the greatest biodiversity on the planet. (Only the soil ecosystem may exceed canopy biodiversity, but we have not yet learned how to make an accurate count of the microorganisms underfoot.) E. O. Wilson, an eminent biologist at Harvard University, has raised Terry's original estimates. By including the canopy, soil, and oceans in his extrapolations, Wilson speculates that as many as 100 million species may inhabit our Earth.

Forest canopies are merely one example of a region on earth that was out of reach to scientists until as recently as twenty-five years ago. When I and other scientists first used slingshots to propel our ropes into the treetops, we did not yet fathom that this green leafy "machine" was a critical component of global health. Now forest canopy scientists, along with reef ecologists, ice physicists, soil biologists, water chemists, and many others, have become the physicians of the planet. We work against a near-impossible timetable in hopes of unraveling the critical mysteries of how our planetary home functions.

With access into forest canopies, our knowledge of biodiversity and the creatures constituting the machinery of forest ecosystems has burgeoned. Accordingly, the role of canopy biologists has changed. No longer can we dangle leisurely from the trees and simply contemplate the beauty of orchids and poison dart frogs; instead, we are caught up in a battle against time to provide answers before the chainsaws dominate. In short, we cannot afford to sleep! To date, biologists have catalogued only 1.5 million species of the alleged 30 million, or perhaps 100 million, species. The pace is slow: taxonomists calculate that we are classifying only the inordinately small number of 7,000 new species per year. Our work is cut out for us. The notion of sorting, counting, and naming 100 million species is daunting. The ecological task of determining which species are critical to essential processes such as photosynthesis, nutrient cycling, and decomposition is even more challenging. Stewart Udall, former U.S. Secretary of the Interior, once said, "Over the long haul of life on this planet, it is the ecologists, and not the bookkeepers of business, who are the ultimate accountants."

Exactly how many is 100 million species? Is there a way to make that enormous number meaningful to those of us who are not mathematicians? We can say that if two hundred scientists discovered and identified one new species every day for the rest of their lives, they would need almost fifteen hundred years (including weekends and holidays) to complete the task of identifying the estimated biodiversity on Earth. Even more urgent than names alone, we need to determine benchmarks for forest canopy health. How many trees and which species are crucial to maintain the global machinery that we call a forest?

Is biodiversity important? Can ecosystems function and remain healthy with fewer species? Unfortunately, no one has the answers to these vital questions. We have not studied our forests long enough to understand the biological processes that are critical to their health. To return to the wisdom of the Sand County Almanac, Aldo Leopold said in 1949, "To save every cog and wheel is the first precaution of intelligent tinkering." This statement, made almost sixty years ago, holds true today. We must preserve all the pieces of ecosystems until we know which are essential to their operation. Forests, after all, are efficient machines that produce energy, medicines, materials, fibers, and foods-and they carry out ecological processes. Their well-being invariably affects human health. Forests may well survive the extinction of some species, but which of these losses exceed the critical thresholds beyond which forests can no longer produce oxygen, cycle nutrients, decompose leaf litter, and carry out all the other services essential to our life on Earth?

These are major issues for our children and their children, as they grow up to become the next stewards of our planet. I hope that we can provide them with an education in science that will equip them to seek solutions. But we scientists need to do more than practice sound science: our research needs to be accompanied by public education and applied conservation, to foster a new environmental stewardship. Forests doubtless house uncharted discoveries for young explorers-new medicines from tropical canopies, exotic fragrances, unique seasonal patterns, unknown creatures buried in the soil. Exciting as the possibilities are, people are not likely to save something they do not understand. Despite the flurry of ecological research over the past twenty years, the Earth has lost an estimated 21 percent of forest habitats. Somehow, scientists have not communicated effectively to the public to ensure stewardship of what they study. Sustainability of our forests is best achieved through education and conservation.

In accordance with this philosophy, I have focused on understanding the energy transfer from leaves to the creatures that consume them (called herbivores), and explaining the importance of this process to the public. Herbivory, the process of foliage consumption, is my scientific specialty. I could thus be described as a professional leaf detective. The major herbivores are insects (such as beetles, caterpillars, walking sticks, true bugs) and mammals (koalas, sloths, and other vegetarians).

The topic of herbivory is complex. Why do insects prefer some leaves to others? Do they like to feed at different heights in the canopy, or on leaves of a certain age? Do they eat by day or by night? In my opportunistic world of canopy research, I sample many leaves, branches, seasons, years, trees, and forests, in order to address the question of how herbivory varies over space and time. I have measured nearly 250,000 leaves in my quest to understand defoliation in forests. My colleagues have jokingly appointed me honorary president of the Leaf Lovers Club.

Measuring leaves is often tedious, even downright boring, work. My database for each leaf includes length, width, area, age, toughness, and types of herbivore damage. Occasionally it also incorporates chemical analysis. Not having access to adequate electrical supplies or a digital computer in the wilds of Cameroon or other remote forests, I have frequently relied on graph paper, tracing leaf samples and counting squares during my nonclimbing hours. To persuade colleagues to count graph-paper squares for me, I have been known to bribe them with Oreo cookies-my staple for survival in the jungle. Back home, I delight in the speed and accuracy of a digitized leaf-area meter hooked up to a computer. My results have documented leaf life span and mortality, the latter frequently caused by herbivores (also referred to as insect pests).

Why is herbivory so important? First, the process whereby insects consume leaves and in turn transfer this energy to the forest floor via their bodies and their frass (droppings) is critical to effective nutrient cycling among the various layers of the forest. Herbivory also creates a catalyst for the production of plant chemicals that defend foliage from animals that would otherwise eat it. Complex relationships have sometimes developed between specific herbivores and their ability to digest the chemicals in a certain type of foliage. This chicken-and-egg scenario is never resolved. Leaves evolve toxins that deter foliage feeders, and herbivores evolve ways to digest those toxins.

The interactions surrounding herbivory are constantly changing, but the end result is a plethora of chemical compounds (many of which have exciting medicinal properties). As ecologists, we become detectives seeking clues to who eats what, what camouflages whom, whose tissue is defended against whom, and which different plant or animal defenses are triggered by chemical or physical traits.

I accidentally stumbled on this ecological battleground. When first undertaking my studies of leaves, I never intended to study insects. I only wanted to find out about leaf growth and turnover of photosynthetic material within the canopy. But the fact that creatures kept nibbling on the marked leaves piqued my curiosity. I began looking at the herbivores in tandem with the leaves and became intrigued by their complex interactions. I also found out that measuring leaves in forest canopies is no simple task. What appeared to be a matter of merely picking ten leaves and measuring their defoliation became a complex chronology of birth, growth, survival, struggle, and death in the treetops. Most insects eat young leaves, but a few also eat older tissue; some insects feed on lower canopies and others on the uppermost foliage; some herbivores take big bites and others simply suck juices.

In no time I had amassed a data set of over a hundred thousand leaves. Even in my initial canopy research in Australia, some leaves lived nineteen years, extending beyond the duration of my anticipated fieldwork. I faithfully checked all marked leaves throughout their lifetimes each and every month, including times when I was pregnant, had toddlers, or juggled my housewifely duties as the wife of a sheep farmer. Some tree species had leaves that lived only six months; those longevity surveys were completed rapidly. I became fascinated by the dynamics of leaf populations in the treetops, and devoted my time to trying to understand the lifestyle of this highly productive component of our planet.

This long span of data collection showed me that, when measured accurately, leaf-area losses in forest canopies approach 15-25 percent per year, a fairly high turnover of green material falling from the treetops via insect digestion and becoming part of the soil below. Scientists measure these processes of energy transfer to understand what keeps forests healthy, just as a doctor measures our blood pressure, heart rate, and other indicators of human health.

(Continues...)

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Excerpted from It's a Jungle Up There by MARGARET D. LOWMAN EDWARD BURGESS JAMES BURGESS Copyright © 2006 by Margaret D. Lowman, Edward Burgess, and James Burgess. Excerpted by permission.
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