What goes on in the uppermost layers of a Smoky Mountain forest? Does anything live up there? And who's going to climb up there to find out? “From charismatic microfauna to megafauna—from water bears to black bears—the forest canopy harbors so much,” says author Rose Houk.
Join us as we delve into one of the ‘missing issues’ of our biannual publication, Smokies Life, to rediscover Houk's article “Life in the Canopy.” Learn about the diverse wildlife that resides in the forest canopy and the risky, physical work required to identify these creatures. This article appeared in Smokies Life, Volume 9, Issue #2, an older issue now out of print. In addition to this special reading, we are resurrecting some of our ‘missing issues’ and providing them free, digitally, through our virtual magazine, Smokies LIVE.
[Old-time guitar music and bird song]
Valerie Polk 00:05
Welcome to Smoky Mountain Air, a new series from Great Smoky Mountains Association where we'll bring you interviews and author readings that delve into the diverse natural and cultural history of Great Smoky Mountains National Park. I'm Valerie Polk, Videographer at Great Smoky Mountains Association.
Karen Key 00:21
I'm Karen Key, GSMA's Senior Publications Specialist. Today we'd like to share a reading from Smokies Life, GSMA's biannual publication. Rose Houk is the author of Cades Cove: Dream of the Smoky Mountains, Smoky Mountain Elk, Pictures for a Park and a variety of other publications for Great Smoky Mountains Association. Rose will be reading her article "Life in the Canopy" which appeared in Smokies Life, Volume 9, Issue 2.
Valerie Polk 00:50
"Life in the Canopy" explores creatures great and small living in the uppermost layers of the forests of the Great Smoky Mountains. The issue of Smokies Life which it appeared in is one of our "missing issues," issues no longer in print. In addition to this special reading, we are resurrecting some of our missing issues and providing them free, digitally, on our virtual magazine, Smokies LIVE at smokiesinformation.org/news. Please enjoy "Life in the Canopy".
Rose Houk (reading) 01:27
"Life in the Canopy"
It was a frigid October morning on Clingmans Dome. The concrete ramp up to the observation tower was slick with patches of ice. Crusty lichens on the trunks of the trees were draped with icicles. Clouds raced overhead, raking the spiked tips of the spruce. People were zipping up their coats and pulling on stocking hats and gloves. One woman, apparently counting on a balmy fall day, was swaddled in a beach towel emblazoned with a brightly colored map of Florida.
We lingered only long enough to soak in the hawk’s-eye view from this high platform—at 6,643 feet above sea level Clingmans Dome is the highest peak in the Great Smoky Mountains, and offers an unfettered sweep of the ridges and mountains and valleys. In every direction too is an impenetrable fortress of green, an extravagance of trees covering nearly every square inch of Great Smoky Mountains National Park.
The Clingmans Dome observation tower bestows a rare above-the-treetop look at the Smokies. Most of the time we earthbound beings must crane our necks up rather than down into the trees. This top-down perspective gives rise to questions: What goes on in the uppermost layers of this forest? Does anything live up there? What creatures big or small live in what’s called the forest canopy? And what is the canopy anyway?
The word “canopy” describes the collective umbrella of trees that arches over the ground in the forest. Some think of it as only the upper story, the highest treetops. To others, it’s everything from where the lowest branches begin, all the way to the tops of the trees—and all the foliage, twigs, branches, plants, animals, even the spaces of air in between. It turns out the canopy is an astoundingly rich, diverse place—some estimates say the earth’s forest canopies hold half of all species in nature.
Yet nobody really knows what that number is because canopy study is a relatively new field. Around the 1970s, scientists began working in tropical forests and the tall trees of the Northwest. They gained access with rafts let down from dirigibles; ropes and climbing equipment; and eventually towers, ziplines, overhead cranes, and suspended walkways. Now, in the Great Smoky Mountains, satellites, lasers, and aircraft are being used to measure the height and growth of trees in the canopy. Webcams, time-lapse photography, and remote sensing add more data about sheer biomass and seasonal changes. Mapping and measuring the canopy can help give a better understanding of its complex, three-dimensional structure.
But the best way to find out what lives up there is to get up in it. Only a few people have actually scaled the lofty heights of the leaf-bound canopy of the Great Smokies forest. Research began about 15 years ago, when the park was launching the All Taxa Biodiversity Inventory (ATBI for short), a program with the ambitious goal of documenting every living thing within its boundaries. Biologist Harold Keller and students from the University of Central Missouri in Warrensburg arrived in the summer of 2000, bringing their curiosity, courage, and climbing ropes on the first comprehensive survey and inventory of tree canopy biota in the park. Keller chose the Great Smokies for the study because the park has more than 130 species of trees, and some of the oldest and largest trees in the eastern United States. The focus of the team was to find out what mosses, liverworts, lichens, ferns, fungi—and myxomycetes—live in the treetops.
Myxomycetes are better known as slime molds. Harold Keller, now professor emeritus, still signs his emails “Dr. Myxos” for his specialty. And it is a specialty, because slime molds undeniably are one of the planet’s more fascinating (some might say sci-fi weird) life forms. Neither plant nor animal, they are in a kingdom all their own, the Protista. From spores, they produce bacteria-eating cells that congregate to form a blob called a plasmodium, appearing in heavy metal pink, yellow, and orange. The plasmodium oozes along on rocks, downed logs, and living tree bark, much like an amoeba, engulfing food as it goes. When mature, slime molds sprout small knobs on stalks that are called fruiting bodies.
To prepare, the students practiced climbing trees and tying bombproof friction hitch knots. They traveled more than 700 miles to Cades Cove in the Smokies, where they started the “adventure phase” of the research. That meant splitting into crews—those who would stay on the ground as spotters, and those who were brave enough to hoist themselves 90 to 100 feet up into trees—about equal to a 10-story building—using a double rope-climbing technique. They had to be on guard for hazards during their aerial explorations—things like bees, bears, snakes, and lightning strikes.
It was risky, physical work. A climber could take two to three hours to shinny up a single tree, scraping off samples of bark every 10 feet, up to almost the tops of various species—red maples, white ash, tuliptree, and white oaks among them. In all, the students went up into some 500 individual living trees over eight seasons in the park.
Sydney Everhart, one of Keller’s former students, was working on her master’s degree on slime molds, and climbing high into the trees to find those “really intriguing creatures.” To decide which trees to climb, she looked for ones with “good limb architecture.” Once she was roped up into a branch, she admitted “there were tense moments for me” especially when she wasn’t in direct contact with the tree itself. About 20 feet up, she’d started thinking “this is a long way” from the ground. But the slime molds called and up she went. That experience eventually led Everhart to her present position on the faculty at the University of Nebraska.
Evenings back in their quarters, the students separated out the mosses, liverworts, lichens, and slime molds. Once back in the lab at college, they rehydrated the samples and managed to identify 55 new records of slime molds in the canopy, including a myxomycete entirely new to science. Student Melissa Skrabal first spotted Diachea arboricola by its tracks and iridescent spores as she climbed a white oak tree. Harold Keller immediately recalls the time and place—July 4 in Whiteoak Sink—one of the most exciting days of the entire project to him, a discovery that exemplified the “serendipity of science.”
He and colleagues contributed another “first” during their work, this one a fern. Polypodium appalachianum is commonly known as the rock cap fern because rocks are its favored habitat. But one of the Missouri students was the first to document this fern rooted in a pocket of “canopy soil” 130 feet up in a giant old tuliptree.
The canopy is chockful of such microhabitats, worlds within worlds that foster all kinds of things, including neat microscopic invertebrates. Among them are the tardigrades, or water bears, animals less than a millimeter long, with cigar-shaped bodies mounted on four stubby legs. Some are armored with an exoskeleton like tiny armadillos. Tardigrade means “slow stepper,” a name given because the organism meanders about in the film of water on mosses, liverworts, and lichens, munching on detritus and things smaller than it is. In the forest canopy, water bears have to survive an environment subject to freezing or drying out. They accomplish that by entering a state of suspended animation. Some have been known to stay inactive for a hundred years, then resurrect when conditions improve. Slime molds and other canopy organisms are also capable of this adaptation.
Insects and other arthropods live in the treetops, at least for parts of their lives, and probably account for most of the canopy’s biodiversity. Mites, springtails, and spiders are abundant in the arboreal world, and so are true insects—the early hairstreak butterfly and great purple hairstreak to name two, along with a bevy of beetles, bees, flies, and ants. Stick insects and katydids are true canopy specialists that spend their adult lives eating leaves of deciduous trees. Then there are the annual “dogday” cicadas that fly about in the treetops, sometimes sucking a little juice from the trees. They have a “divided allegiance between ground and canopy,” notes entomologist Chris Carlton. In the nymph or immature stage they stay underground for years (some as long as 17 years), sucking precious fluid from roots. They emerge from the soil in the hot summer days of July and August, climb up and shed their exoskeletons, then fly back up into the trees. In late summer, the raspy sound echoing in the woods is adult male cicadas trying to attract females. Once they’ve mated, the females deposit eggs on small scars they saw into twigs, the nymphs hatch and drop to the ground, and the cycle begins anew.
Some land snails head up into the trees too. One species of mountain tigersnail, with a gorgeous spiral shell of contrasting stripes, was seen 70 feet up in a tree.
From charismatic microfauna to megafauna—from water bears to black bears—the forest canopy harbors so much. Black bears, the iconic big mammals of Great Smokies, spend a lot of time in trees. Park wildlife biologist Bill Stiver points to several ways they’re adapted to an arboreal existence. Bears, even newborn cubs, have impressive curved claws for climbing; they use those claws with extreme efficiency as they scurry up a tree. How high can a bear go in a tree? “As high as they want to,” replies Stiver, “to the tippy top.” And as any Smokies backpacker knows or quickly learns, you have to hoist your food bag on a cable between trees, and high enough to be out of a bear’s reach. Bears always seem to be hungry, and they get essential food from trees throughout the year—leaves and buds in early spring; fruits in summer; and acorns, hickory nuts, and beechnuts in fall. They’ll knock down branches to reach a tasty bunch of ripe black cherries, or impatiently rip away oak branches to get at acorns in their fall feeding frenzy. During winter, Smokies bears choose hollows in large, old trees for dens, sometimes 20 to 80 feet aboveground, and females give birth to cubs in these dry, secure cradles. Trees also serve as resting places—it’s not unusual to see a black bear dozing on a branch during a daily siesta.
Squirrels—gray and red—nest in the canopy and find food there, including acorns and nuts and buds and fruits, especially from oaks, black gum, and beech. They build nests of leaves and twigs in the crotch of a tree or in a cavity. Gray squirrels are especially agile tree dwellers; red squirrels, or “mountain boomers,” often elicit their noisy calls out on a branch.
Those squirrels are active in daytime, while a relative—the flying squirrel—is a creature of the night. Both northern and southern flying squirrels are found in the park. The northern flying squirrel, at the south end of its range in the Smokies, is an endangered species. In winter they huddle in hollow cavities in yellow birch or beech, but in summer they also make nests of sticks, called dreys, in conifers. The southern flying squirrel is more common and lives mostly at lower elevations. Both are supremely equipped to navigate the canopy. Flying squirrels don’t actually fly, but glide by means of folds of skin that extend from wrist to ankle. The membrane forms a furry cape that acts like a wing when stretched out; the tail works like a rudder for controlling their aerial maneuvers. Flying squirrels may best be seen by full moon on a summer night, gliding maybe 30 feet or more from treetop to mid-trunk. They can also leap from tree to tree or run along a branch. Their favored food is also acorns and nuts, which they store in the cavities and forks of trees, along with buds, blossoms, and berries. During their movements, flying squirrels must beware of tree-climbing snakes, various mammals, and birds of prey.
Bats are mammals that do in fact fly, and they also inhabit the canopy. In the park, red bats flit through the foliage foraging for insects. In the park, the less common Indiana bat selects the “pop” bark of dead pines, mostly white pines, contrasting with their use of oaks in the Midwest. They’ve been known to move from tree to tree, and when an old tree falls they will find another; so standing dead snags are most valuable to them. Little brown bats and northern long-eared bats also use snags. They locate their maternity colonies under tree bark—one slab of bark might shelter 80 to 100 bats.
Naturally birds are the most obvious tree dwellers, so many it’s hard to list them all—whether flying over, nesting in, or finding food in the canopy. Broad-winged hawks are the quintessential hawks soaring close to the treetops, in summer searching for unwary squirrels and in early fall rocketing past on southbound migrations. Owls, heard more than seen, are there too. In a dim cove, even in daytime, you may hear the riveting call of a barred owl: who cooked for you, who cooked for you all? Northern saw-whet owls are most likely heard in the deepest spruce-fir forest on clear, moonlit summer nights. For them, the canopy provides roosting and nesting places.
Among smaller songbirds, scarlet tanagers and vireos come to mind as denizens of the mature forest, along with the flycatchers, including the Eastern wood-peewee, which perches on dead branches to feed, preen, and sing. Different birds tend to partition the canopy—scarlet tanagers and red-eyed vireos, for example, put nests 20 to 30 feet up in a tree, while Eastern wood-pewees and yellow-throated vireos prefer the top suite. A bewildering array of warblers—cerulean, blackburnian, and several others—feed in the treetops. Those and other birds that migrate into the Smokies in the spring from the tropics depend on the solid green swatch of forest for a big part of their existence.
With so many habitats and so much moisture, the Great Smoky Mountains support an astounding roster of amphibians. But almost all the salamanders, turtles, frogs and toads are terrestrial. Cope’s gray treefrog is one exception. This small to medium-sized frog, the only true treefrog in the mountains, has been found only on the Tennessee side of the park, mostly below 2,000 feet in elevation. The gray-green spots on its back appear much like the splotchy lichens that grow on tree bark, permitting perfect camouflage in its native habitat. Enlarged pads on the tips of the toes help these skillful climbers gain traction even on vertical surfaces. During breeding season, beginning around early April, the males send up a chorus of fluty trills from the trees as they move to ponds to meet up with females. Other than these mating trysts, Cope’s gray treefrogs spend the rest of the year in the trees. Kenneth Dodd, who’s studied amphibians in the park for many years, declared that a walk in Cades Cove during late spring or early summer “with the new flowers in bloom and Cope’s Gray Treefrogs trilling and resonating from the surrounding treetops, is one of the many little pleasures” of studying these creatures.
In the Smokies, the canopy includes not only the grandest oldest trees, but also second- and third- growth forest that has come in since logging days and park establishment. Adding to the complexity are several forest types—from the highest elevation spruce-fir, to beech and birch, drier pine-oak, and the classic cove hardwoods, the tallest and most developed canopy in these mountains.
Paul Super gets to watch what goes on in the treetops more closely than most. As science coordinator at the Appalachian Highlands Science Learning Center on Purchase Knob on the North Carolina side of the park, he sees the verdant vegetation of the deciduous forest canopy for six months of the year. Yet that’s not the first image that comes to his mind. To Super “the exciting thing about the canopy is that it’s where the sun reaches the ground.” He’s thinking of the canopy during the other half of the year, when the leaves have fallen and light shines on the forest floor. Come springtime that light lets the vernal wildflowers bloom, a floral show unequaled almost anywhere in the country. But, once the trees fully leaf out again, sunlight shimmers in the top branches but struggles to break through the thick foliage to reach the ground. Then only shade-loving flowers can bloom. In autumn, the leaves and other “stuff” from the canopy drop to the ground. So the forest is a big recycling machine, a cycle that’s profoundly significant to the canopy ecosystem and all it harbors.
The canopy doesn’t exist in isolation. Water and nutrients from the soil are drawn up into the treetops to nourish growth and photosynthesis. The trees themselves are competing to see which can grow the tallest to reach precious sunlight. The canopy is also the “cell membrane,” says Super, where forest meets sky, the point where trees absorb all that the atmosphere brings—rainfall, fog, dew, sunlight, gasses—essential elements like nitrogen and carbon dioxide but also pollution such as acid rain, ozone, and greenhouse gasses. The canopy is a buffer, but its capacity is not unlimited.
In talk about the canopy, Smokies scientists often speak about “disturbance”—both natural and foreign. Natural disturbance comes in the form of wind, even very strong winds like tornados that quickly uproot whole swaths of trees. There’s also the natural decay and death of individual trees that sends them crashing to the ground. Such disturbances create “light gaps,” openings where new seedlings and young trees sprout as the canopy continues to go through dynamic changes. Then there are the exotic foreigners, especially insects like woolly adelgids that have wreaked havoc among the park’s grand eastern hemlocks and Fraser firs. The demise of most of the Fraser firs is startling from the Clingmans Dome tower. With their passing, one of two dominant evergreens is greatly diminished, leaving a gap in the high-elevation canopy. What will take the place of the firs? What about the slime molds, mosses, lichens, and insects that lived on and in them? Where will the northern flying squirrels glide, and northern saw-whet owls hide?
So many questions, so much more still to learn about life in the forest canopy. Student Melissa Skrabal, who discovered that new slime mold, described her feelings when she climbed into the trees: “A flood of roller coaster emotions bubbled up each time I swayed to and fro at unbelievable heights in the treetops of the old growth forests of the Smoky Mountains. I had gone where nobody has ever gone before.” In the biological frontier of the forest canopy, untold discoveries remain to be made by new pioneers.
[bird songs fading into Old-time guitar music]
Valerie Polk 21:26
Thank you to Rose Houk for her fascinating article. Look for more episodes in our series Smoky Mountain Air from Great Smoky Mountains Association to come soon. Our theme music is from Old Time Smoky Mountain Music, GSMA's Grammy-nominated music collection available at SmokiesInformation.org. Bird recordings by Mark Dunaway. Thanks for listening!