The Forest Unseen: A Year's Watch in Nature (12 page)

Peach turns to pink, and color spreads wider over the horizon. The sky’s vault brightens enough to reveal the partly closed chickweed
flowers in the mandala and to give form to the boulders and stones that define the mandala’s edge. As the world fades into view, Carolina wrens sing, vying with the waterthrush to produce the loudest song in the woods. The wrens sing year-round, but today I hear them with fresh ears, the familiarity of their song stripped away by the springtime flush of sound. No other bird, save the now-departed winter wren, can match the vigor of their acoustic attack or the exuberance of the uncoiling energy in their song.

The wren’s music is answered by a Kentucky warbler from farther down the slope. The warbler echoes the wren’s theme and tone but holds back, like a diver bouncing endlessly on a board, never daring to take the plunge. Then another song bursts from the canopy, lisping like a black-and-white warbler, but the song breaks out of the pattern, accelerates, then twitters. I cannot identify the bird and, more frustratingly, cannot find it with my binoculars. Perhaps this is the dawn “flight song” of a warbler? These flight songs are out-of-character virtuoso solos given during arching flights high above the forest. They are seldom recorded and, in my limited experience, are highly variable. What role they play in the birds’ lives is unknown but, if nothing else, they must provide a rush of creative release for birds that spend the rest of their day repeating just a few syllables.

Woodpeckers add their boisterous voices to the performance. First the red-bellied woodpecker lobs its quivering cry across the mandala, then an answer flies back, the maniacal laugh of the pileated woodpecker. Blue jays punctuate the woodpeckers’ volley with alternating rasps and whistles. As the glow in the sky intensifies, half a dozen goldfinches fly eastward, bouncing in the air just above the forest canopy, like flung stones skimming over water. Each bounce is accompanied by a twitter,
ti-ti-ti, ti-ti-ti
.

The whole sky flashes pink for a moment, then yellow surges up from the east, brightening the mandala. Color sinks back to the horizon again, leaving milky light across the rest of the sky. A red-eyed vireo greets the glow with his regularly spaced bursts of whistling. Some
bursts end on a rising note, “where am I?”; others conclude on a low note, “there you are…” The vireo questions the forest, then answers over and over, lecturing into the midday heat when other birds have retired from the podium. As befits his professorial temperament, the vireo seldom descends from the heights of the canopy and is usually detected only through his bright, repetitious song. The vireo is joined by a brown-headed cowbird. Cowbirds are brood parasites, laying their eggs in the nests of other birds. This emancipation from parental duties leaves the cowbirds free to pursue the pleasures of courtship. The male’s song has taken him two or three years to perfect and sounds like molten gold falling, solidifying, then ringing out as it strikes stone. A burst of precious liquidity combined with the ringing of metal.

The heavens shine blue now, and the sunrise’s colors have faded to a pastel belt of cloud in the east. A northern cardinal chips loudly on the slope below the mandala, each note like struck flint. These crisp calls are the counterpoint to turkey gobbles rising up from the valley below. The forest has muffled the turkey’s distant sounds, adding what Thoreau called the “voice of the wood nymph” as the sound is bounced and squeezed through the vegetation. We are in turkey-hunting season, so the gobbles are as likely to be gobble-mimicking humans on a gastronomic quest as they are real turkeys searching for love.

The fading dawn colors revive momentarily, and the sky shines with lilac and daffodil, layering colors in clouds like quilts stacked on a bed. More birds chime into the morning air: a nuthatch’s nasal
onk
joins the crow’s croak and a black-throated green warbler’s murmur from the branches above the mandala. As the colors finally fade under the fierce gaze of their mother, the sun, a wood thrush caps the dawn chorus with his astounding song. The song seems to pierce through from another world, carrying with it clarity and ease, purifying me for a few moments with its grace. Then the song is gone, the veil closes, and I am left with embers of memory.

·   ·   ·

The thrush’s song flows from the syrinx buried deep in his chest. Here membranes vibrate and squeeze the air that rushes out of the lungs. These membranes circle the confluence of the bronchi, turning a toneless exhalation into sweet music that ascends the trachea and flows out of the mouth. Only birds make sound this way, using a biological hybrid between the flute’s swirling tube of air and the oboe’s vibrating membranes. Birds change the texture and tone of their songs by adjusting tension in the muscles that wrap the syrinx; the thrush’s song is sculpted by at least ten muscles in the syrinx, each one shorter than a grain of rice.

Unlike our voice box, the syrinx offers little resistance to the flow of air. This gives small birds the ability to ring out louder songs than the huskiest human. But despite the efficiency of the syrinx, birdsong seldom carries farther than a stone’s throw. Even the turkey’s explosive gobble is quickly swallowed up by the forest. The energy that propels the sound is easily absorbed and dissipated by trees, leaves, and the sponginess of air molecules. High-pitched sounds are more easily absorbed than bass notes, whose long wavelengths let them flow around obstacles rather than bounce away. The beauty of birdsong, especially descant birdsong, is therefore a blessing available only at close range.

Not so the sun’s gift. The photons that created this dawn have traveled one hundred and fifty million kilometers from the surface of the sun. But even light can be slowed and filtered. This slowing is most dramatic inside the sun’s belly, where photons are born from the fiery union of pressurized atoms. The sun’s core is so dense that it takes ten million years for a photon to struggle to the surface. Along the way, the photon is continually blocked by protons, which absorb the photon’s energy, hold it for a moment, then release the energy as another photon. Once the photon finally bursts free from millions of years trapped in the sun’s molasses, it zips to earth in eight minutes.

As soon as photons reach our atmosphere their paths are again strewn with molecules, albeit molecules that are millions of times less densely packed than those in the pressed mass of the sun. Photons
come in many colors, and some colors are more vulnerable to being impeded by the atmosphere. Red photons have wavelengths that are much longer than the size of most air molecules, so, like a turkey gobble in a forest, they flow easily through the air and are seldom absorbed. Blue photons have wavelengths that more closely match the size of air molecules, so this short wavelength is absorbed by the air. An air molecule that absorbs a photon jiggles with the excitement of the ingested energy, then pops out a new photon. The ejected photon is shot out in a new direction, so the tidy stream of blue photons is scattered into a ricochet of light. Red light is not absorbed and scattered, so it flows straight on through. This is why the sky is blue; we are seeing the redirected energy of blue photons, the glow of billions of excited air molecules.

When the sun is overhead, photons of all colors reach our eyes, even though some blue ones are redirected along the way. When the sun is low on the horizon, photons have a sloping path to cut through the air, so more blue light is stripped out. The red dawn light bathing this Tennessee mandala was therefore born in the blue morning skies over the Carolina mountains to the east.

The light and sound energies washing over the mandala find a point of convergence in my consciousness, where their beauty quickens a flame of appreciation. There is convergence also at the start of the energy’s journey, in the unimaginably hot, pressurized core of the sun. The sun is origin of both the dawn’s light and birds’ morning songs. The glow on the horizon is light filtered through our atmosphere; the music in the air is the sun’s energy filtered through the plants and animals that powered the singing birds. The enchantment of an April sunrise is a web of flowing energy. The web is anchored at one end by matter turned to energy in the sun and at the other end by energy turned to beauty in our consciousness.

T
he springtime flush of flowers is over. A few chickweed flowers and a geranium are all that is left of the month’s glory. Spent flowers rain down from above, bringing to earth evidence of the maple and hickory trees’ prodigious reproductive efforts. Hundreds of maple and hickory flowers are lying within the mandala. Unlike the gaudy blooms of the spring ephemerals, these tree flowers are bland and unassuming, with no obvious petals or colored adornments. This extreme Puritanism of dress suggests that sex among the mandala’s trees is a business very different from the ephemerals’ effusive festival of nectar and color. These trees have no one to impress. Wind carries their pollen, so insect eyes and palates need not be bribed; flowers can be stripped down to their utilitarian essentials.

Pollination by wind is a particularly useful strategy for early-blooming trees. The spring ephemerals live in a relatively warm, sheltered microclimate, yet they struggle to find pollinators. The tree canopy’s microclimate is more exposed and is even less friendly to the insects of early spring. Wind is not in short supply, however. Maples and hickories have therefore broken the ancient contract with insects, using physical rather than biological methods to transport their pollen. Increased reliability comes with an unfortunate decrease in precision. Bees deliver pollen directly to the stigma of the next flower. Wind does not deliver anything. Rather, it disperses whatever is caught in its motion, much to the distress of both flowers and human sinuses.
Wind-pollinated plants must therefore release vast drifts of pollen. They are like castaways stranded on an island, throwing millions of bottles into the water for want of a dependable postal service.

Unlike the hermaphroditic wildflowers, maple and hickory produce two kinds of flower, male and female. Male flowers dangle from twigs so that the slightest movement of air will stir them. Maple trees hang clusters of these flowers from wiry filaments. Each filament is a centimeter or two long and ends in a tuft of anthers, pollen-producing structures that look like tiny yellow balls about the size of a comma on this page. Hickory’s anthers are strung on fuzzy garlands called catkins, each one about as long as a finger. In both species, the anthers nestle in groups under small umbrellas, presumably to stop the rain from washing pollen away. The female flowers are more stubby, having no need to cast large quantities of pollen into the wind. Their stigmas intercept wind-borne pollen to start the fertilization process. Little is known about the aerodynamics of the stigmas, but they seem to be placed in the windiest parts of the plant and to be designed to encourage air to curl around them, forming eddies that slow the air and thus deposit pollen grains.

By this time in the season, male flowers have shed their pollen and, their task completed, have been discarded by the trees, leaving the mandala covered with tangles of yellow-green filaments and catkins. But the work of the female flowers has just begun. The fertilized eggs inside these flowers will take months to mature into fruit. Mature hickory nuts and maple seeds will not be ready to drop until autumn.

Wildflowers do not have the luxury of months of summer sun to fuel their fruiting. Most spring ephemerals fruit just a few weeks after their bloom, completing all their reproduction for the year before summer’s thick tree canopy chokes off the light. I walk around the mandala’s edge to search for the
Hepatica
plant whose flower I watched open in March. I find it just behind the spicebush, its liver-leaves splayed wide and the flower stalk holding up a bouquet of fat green torpedoes, each one the size of a small pea. Several of these fruits have
tumbled to the ground, revealing a blunt white nipple at their base, a bulbous center, and a sharply tapered tip. This sharp tip is all that remains of the style, the short stalk that supported the stigma. The green swelling is the ovary wall, which now encloses a fertile seed.

An ant approaches one of the fruits, palpates it with her antennae, and crawls on top of the fruit. She scurries back onto the leaf litter, grasps the fruit, then abandons it. Another ant repeats the process a few minutes later. Each time the fruit moves a few millimeters, but the ants then leave. Half an hour passes and more ants walk by, ignoring the fruit. Then a large ant appears, tickles the fruit with her antennae, and seizes it with the hooked mandibles that jut from either side of her mouth. The fruit is as large as the ant, but she raises it high above her head, mouthparts firmly planted in the fruit’s blunt white end. She sets off for the center of the mandala, stumbling over maple flower stems, recovering, falling into leaf crevices, crawling onward. Her path is tortuous, circling back to bypass gashes in the leaf litter, walking backward through tangles of catkins. I get caught up in her struggle and exhale sharply with relief when she reaches a penny-sized hole in the litter and ducks down. I peer into the ant hole and see the green glow of the fruit being jostled and rotated by a small group of ants. Gradually the glow fades as the fruit is swallowed by the ground, a foot away from where it fell.

The
Hepatica
fruit’s odyssey is part of a larger saga, linking the stories of forest ants to those of spring ephemerals. The white nipple at the tip of the
Hepatica
fruit is an elaiosome, a fatty treat cooked up by the plant especially for ants. Such rich food is seldom found in convenient, undefended packages, so ants quickly carry elaiosome-bearing fruits to their nests, where the food parcel is chopped up and fed to the colony’s larvae. The next generation of ants will be partly made from
Hepatica
flesh. Once the elaiosome has been removed, the ants dump the inedible seed into their nest’s compost heap. Thus the fastidious tidiness of the ant colony places the seed in loose, fertile compost, the perfect place for germination.