Stephen Mulkey remembers the first moment he poked his head through the thick mesh of leaves covering a tropical forest.
After his eyes adjusted to the flash of sunlight, Mulkey saw a vast green roof teeming with an array of novel insects, plants, birds, bats and monkeys."It was like being on a different planet," he said. "It was absolutely thrilling. Suddenly you're in a whole new biological world."
Mulkey, 40, is a biologist with the International Center for Tropical Ecology at the University of Missouri at St. Louis. The Missouri native ventures to Panama for several one-month trips a year.
His latest research project is high in that top carpet of green in a forest near Panama City. It's a frontier rarely reached by scientists.
Until recently, Mulkey had his feet on the ground in science. But late last year he entered the strange new world of tropical treetops.
He got there by riding in a cagelike, steel gondola lofted by a construction crane. The crane has been rented by scientists with the Smithsonian Institution, which maintains a research institute in Panama.
The aim of his long-term project is to find out how the often-harsh conditions in the treetops affect the way trees and other plants grow.
Mulkey, who teaches plant physiology and general ecology at UMSL, must keep an eye out for such ever-present dangers as snakes and Africanized honeybees when he's studying the forest.
The so-called killer bees live in crevices in the treetops. They are easily angered when their nests are accidentally disturbed. They have attacked other scientists with deadly vengeance.
To protect himself, Mulkey carries a carbon dioxide fire extinguisher. The extinguisher's cold gas can immobilize the bees - hopefully long enough for him to escape in the slow-moving gondola.
"I can't run when I'm up there," he said in an interview in St. Louis between two journeys to Panama. "There's no place I can go if I disturb a nest. It's literally life and death."
Tropical biology is, indeed, a contact sport.
The upper canopy, as scientists call the top layer of leaves and branches in a forest, is a living boundary between the atmosphere and a sea of diverse life in the tropical forest below.
Only in the past few years have researchers begun to give much attention to the upper canopy. Much of the delay was a result of its being so hard to get to.
To reach it, some scientists perfected their tree-climbing skills. But most of the tree-climbers ended up sweatily struggling through the treetops like exhausted monkeys.
Others, no doubt with visions of Spider Man, fashioned elaborate networks of ropes, pulleys and walkways.
French researchers even dropped a giant, inflatable raft onto the treetops from a dirigible. Imagine Dumbo the elephant settling on a bed of upright toothpicks.
But these methods are either dangerous, hurt the treetop environment, don't get scientists where they want to go for as long as they need - or all of the above.
Meanwhile, the lack of research on the upper canopy has blocked answers to important questions about global climate change and species extinction. Among them: What is going on up there that may increase or decrease global warming brought on by man-made pollution?
The answers to these and other questions are needed before key environmental and conservation decisions can be made, Mulkey said.
Enter the bright red canopy crane.
The $250,000 crane rents for $8,000 a month. Smithsonian scientists first used it on a trial basis in September 1990.
The forest canopy in Mulkey's study area is about 100 feet tall, roughly the same height as an eight-story building. The canopy crane towers an additional 40 feet or so above that.
Riding in the gondola, Mulkey is lowered into the canopy with his sewing-machine-size gas analyzer like an astronaut coming in for a landing in an alien landscape.
The advantage of the canopy crane is that it doesn't destroy the treetop environment, and it can get scientists to every tree in a 60-yard radius - about 30 or 40 trees.
Every hour or so, Mulkey leans over the edge of the gondola and clamps an aluminum and plastic chamber over a leaf. The chamber is connected to the computerized gas analyzer.
The analyzer measures gases that leaves take in and give off as part of their metabolism - the process by which living things make energy and materials for growth.
"It's like measuring your metabolism when you first get up in the morning and again after you just ate a Thanksgiving dinner," he said.
But rather than a turkey with trimmings, the plant has feasted on a day's worth of sunlight and carbon dioxide gas.
He also analyzes leaves for a wide range of other essential chemicals. In all, he will study a dozen species of trees in several locations and at different times of year.
Within this unexplored domain may live an insect or plant species that produces a chemical weapon against cancer or some other human disease. Only a small fraction of the world's 250,000 higher plants have been studied for useful drugs, but they have yielded medicines for such diseases as high blood pressure, childhood leukemia, Hodgkin's disease and glaucoma.
The world beneath the tropical forest canopy is largely dark and humid, no matter what the season. But in the upper canopy, scientists are discovering, it's an entirely different story.
There, the forest is exposed to windier, drier and brighter conditions. Changes in temperature and humidity are greater - both daily and seasonally. And plants in the upper canopy are exposed to more pollution and radiation from he sun.
"Upper-canopy plants are facing environmental extremes of very dry in the dry season, where there's no rain at all, to 1,500 millimeters (about 60 inches) in the rainy season," Mulkey said. "Although we think of the tropics as having a very constant environment, the upper-canopy environments represent extremes virtually unknown outside the tropics."
So how do trees deal with it?
"We're really talking about an economic question," he said.
That's because plants invest their resources in different ways, depending on the types of leaves they produce. For instance, a thick, drought-resistant leaf loses less water during the dry season than a thinner leaf. But a thinner leaf can be better at trapping light and providing more energy for the tree to grow.
Scientists know that as seasons change in the tropics, trees produce leaves of various kinds at different positions in the canopy. But researchers don't know how trees operate in the upper canopy.
That's what Mulkey aims to find out.
Specifically, he will study the way trees make leaves, fruits and flowers in the upper canopy during different seasons. Does the stress of drought during the dry season slow leaf production? Does a drop in the amount of sunlight during the rainy season put a damper on fruiting and flowering?
Such bits of information are like bricks. Mulkey and other scientists are gathering them as they prepare to rebuild tropical forests, which humans are now cutting at an increasing rate - more than 1 acre a second, he said.
"We're at the point now where we're no longer faced with saving ecosystems that remain," Mulkey said. "We're going to be faced with reconstructing the ecosystems that have been destroyed."