The Forest Unseen: A Year's Watch in Nature

by DavidGeorge Haskell

  Maples try to buy a ticket on the Mayflower by contriving to launch seeds into gusty updrafts. They do so by preferentially releasing seeds in the upward-blowing air of eddies and gusts but holding tight in downdrafts. Many wind-dispersed trees concentrate their seeds at the top of the canopy, increasing the chances of launching a seed that can catch an updraft. Maples in the mandala have an extra advantage. The prevailing winds blow unobstructed across the valley below and are then deflected upward by the steep slope on which the mandala sits. The wind therefore gives the mandala’s seeds an extra skyward puff in their fight against gravity.

  Each tree casts a “seed shadow” that is darkest, most densely packed with seeds, in the tree’s immediate surroundings but theoretically extends across the entire continent. A glance upward confirms that the maple seeds that flutter onto the mandala are almost all the stay-at-home variety, having fallen from trees within easy gliding distance. Mixed among them are a very small number of competitors from other parts of this forest, or perhaps a rare seed that traveled here on a thermal updraft, like a vulture, from tens or hundreds of miles away.

  The long reach of seed shadows makes the study of seed dispersal difficult. It is easy to gather information about the vast majority of seeds that stay close to their parents. But the offspring that get flung into the open sky are nearly impossible to track—yet they are the key players in the grand story of each species’ history.

  Lacking a drone spy plane with which to track soaring seeds, I turn my attention to the maple seeds on the mandala’s surface. The diversity of forms is remarkable, particularly in the shapes of the wings. Some have three times the surface area of others. A few are ruler-straight; others curve downward like a boomerang, and others arch upward. On most seeds, a notch indents the wing where it meets the seed, but some are notchless. The angle and depth of the notch varies, as does the fatness of the wing. The mandala is a botanical air show, with every airplane wing shape on display, and a few shapes that no human engineer would dare use.

  The diversity of shapes causes the maple seeds to fall with very different styles. The most obvious seeds are those that don’t fly but plummet. One in five seeds lands joined to its sibling. These pairs don’t spin at all but plunge and smack into the ground under the tree. Singletons with small or hunched wings also drop without spinning. These are exceptions, however. Most seeds fall freely for a second or two, and then start to spin. The wing rotates so that its rib, the fatter edge, slices through the air with the wing’s thin vein following. This spinning airfoil generates lift, slowing the fall. A drifting seed can obviously glide farther from the parent than can a seed that falls like a stone. But the extra time in the air also increases the likelihood that a turbulent updraft will cause it to float upward. Whether through shallow descent or lucky ascent, the wind smears the trees’ seed shadows outward, reducing competition among siblings and dropping hopeful progeny across a wide area.

  Botanists call seeds that produce their own lift samaras. Technically, a samara is not a seed but a special fruit, formed by the mother’s tissues, holding the seed inside. Ashes and tuliptrees also produce samaras, although neither generates the same amount of lift as the maple’s spinning blade. The maple’s asymmetry gives it an advantage. Its samara is designed to flow through the air like a bird or an airplane wing, with a slicing leading edge. Ash and tuliptree samaras are symmetrical and cannot achieve the maple’s elegant spin. Instead, they twist rapidly about their long axes as they fall, preventing the wing from biting into the air. These species rely less on their own airfoil and more on the strength of the wind to carry their seeds. Accordingly, ashes and tuliptrees cling tightly to their samaras, letting them go only when the wind rages hard.

  Maple samaras live in a little-known border country between the aerodynamics of fast, large objects, like cars and airplanes, and the aerodynamics of slow, minuscule objects, like motes of dust. Airplanes experience their surroundings as relatively free of friction, but dust flecks are so small that friction is about all that they experience. In other words, as an object gets smaller, its world comes to resemble a jar of cold molasses: hard to swim through but easy to float in. The size and speed of samaras puts them in low-grade maple syrup, perhaps appropriately. Engineers have shown that this syrupy air forms a swirl over the leading edge of a rotating blade. This miniature vortex sucks on the upper surface of the spinning samara, slowing its descent.

  The aerodynamic consequences of the variety of maple samara shapes are hard to assess. But students of maple samaras have tossed seeds from balconies and drawn two general conclusions. First, wide wingtips produce turbulence and likely slow the wing’s spin, reducing lift. Curved wings are likewise less able to generate lift than straight wings. So, fat-tipped, curvy samaras are poor fliers in the ordered air of a laboratory building. But most of the seeds in the mandala have fat tips and curves. Are the samaras defective versions of an elusive perfect form? Or do maples know something that we do not about the advantages of fat-tipped, curved, or otherwise “deficient” wings?

  Wind in a forest is a confusion of swirls and puffs. The forms of the samaras seem to me to be botanical incarnations of the wind’s complexity: a wing for every eddy, a curve for every gust. This diversity of biological form is not restricted to samaras but is a general theme in the forest. Close examination of almost any structure here—leaves, animal limbs, twigs, or insect wings—reveals variability everywhere. Some of this irregularity comes from the different environmental contexts that individuals find themselves in, but much of it has deeper roots in genetics, made possible by the reshuffling of DNA in sexual reproduction.

  The fact that individuals differ subtly from one another seems a minor detail of natural history, but such variability is the basis of all evolutionary change. Without diversity, there can be no natural selection and no adaptation, as Darwin knew when he devoted the first two chapters of On the Origin of Species to variation. The samaras’ diversity therefore points indirectly to the invisible workings of evolution. From these varied forms will be chosen the next generation of maples, specially adapted to the winds blowing through this mandala.

  October 29th—Faces

  Squalling bands of cold rain scoured the forest last week, bringing to ground the first significant accumulation of leaves. Now a strong sun has baked the leaf litter, and every moving animal stirs up loud rustling. Crickets and katydids are quickened by the warmth, and they sing with vigor: regular high pulses from crickets hiding beneath downed leaves and raspy trills from angle-winged katydids clinging under branches. Unlike the dawn chorus of birds in the springtime, the fall-breeding crickets are loudest in the midafternoon, when their bodies have sponged the day’s heat.

  The precise songs of insects are punctuated by untidy crackling sounds. A gray squirrel shambles toward the mandala, intermittently plunging its nose into the litter. The squirrel seems fevered, its body trembling with disorganized energy. The animal continues alternate surges and rummaging until it reaches a tree, where it scrabbles up and disappears from view. A few minutes later it descends, headfirst, with a hickory nut in its mouth. The squirrel catches me with its dark eyes, then freezes. Its head is held tipped up, and the tail straightens parallel to the tree trunk. The squirrel watches. Then trembling waves agitate the tail. The fur on the tail flattens, turning a brush into an undulating fan.

  I hear quiet drumming as the tail pulses. Somehow, the flattened tail is substantial enough to beat out a warning tattoo on the trunk. I have seen the tail-fluttering display many times but have never been close or quiet enough to hear the subtle tapping. This novelty is not just a consequence of my weak powers of observation—I am likely not the intended recipient of the signal. Gentle drumming sounds carry poorly through air, but the vibrations move with great efficacy through wood. Other squirrels in this tree, especially those in tree holes, will hear the warning through both their ears and their feet.

  The squirrel completes its descent in spurts, alternat
ing stationary drumming with darting rushes down the trunk. It reaches the ground, runs to the far side of the trunk and, after poking its head out from behind the tree to glance at me one last time, bounds away, the hickory prize locked in its jaws.

  The drumming squirrel was not alone. Within five meters of me at least four other squirrels ply the mat of leaves, with more above in the branches. The hickory adjacent to the mandala is one of the few trees in this patch of forest with nuts still falling, making it a popular destination for squirrels, whose winter survival depends on body fat and nut stores. Competition among the foragers stirs up a frenzy of crinkling leaves and chittering mouths.

  I sit and listen as the afternoon turns to evening. The squirrels’ urgent sounds rise and fall against the backdrop of the constant, mellow trilling of crickets. As light starts to dim, a new sound pushes into my awareness. The sound comes from behind me, upslope. I am loath to swing around and startle whatever animal is making the unfamiliar noise, so I sit motionless and focus on the sound. Unlike the nose-pushing or bounding of squirrels, this sound is steady, a continuous rustle, getting louder, like a large ball rolling through the litter. The strange sound builds. It is headed directly at me, and I feel a small surge of anxiety. Slowly, I twist just my neck, hoping to steal a glance.

  Twelve paws paddle the litter as three raccoons trundle toward me. Their movement is focused, calm, and purposeful. They seem to glide down the hill, like mammalian caterpillars, fuzzed in silvery gray. They are slightly smaller than the adults that I see in these parts; perhaps they are young of the year, born this spring.

  I sit directly on the line of the raccoons’ path, and they come within a foot before abruptly stopping. My neck is turned the wrong way, so the animals have moved out of sight. I pour my attention into my ears. The raccoons puff and sniff as they stand, making a nasal investigation. After half a minute, one snorts gently, giving a soft, fleshy oink. At this, all three continue on their path, skirting me by a foot or two. They show no sign of alarm as they come into sight, then pour away down the hill.

  My first reaction to the raccoons was that of surprise, a jolt of excitement as the strange sound resolved into the advancing trio. Then the raccoons’ appealing faces came close: dark velvet masks set in crisp white borders, obsidian eyes, rounded ears perked jauntily, and slender noses. All this set in ruffs of silver fur. One thing was evident: these animals were adorable.

  My zoological self was immediately embarrassed by these thoughts. Naturalists are meant to have outgrown such judgments. “Cute” is for children and amateurs, especially when applied to a common animal like a raccoon. I try to see animals for what they are, independent beings, not as projections of desires leaping unbidden from my psyche. But, like it or not, the feelings were there. I wanted to pick up a raccoon and tickle it under the chin. Surely this was the ultimate humiliation of the zoologist’s scientific hauteur.

  Darwin might have sympathized with my plight; he knew the emotional power of faces. In The Expression of the Emotions in Man and Animals, published a decade after On the Origin of Species, Darwin explained how human and animal faces reflect emotional states. Our nervous systems scribe our inward feelings onto our faces, even when our intellect would rather conceal what is within. Sensitivity to the nuances of facial expression is a core part of our being, Darwin claimed.

  Darwin focused on the nervous and muscular mechanisms that translated emotions into facial expressions, implicitly assuming that observers of faces would interpret them correctly. In the early and mid-twentieth century, Konrad Lorenz, one of the first proponents of the evolutionary study of animal behavior, made explicit what Darwin had assumed. Lorenz analyzed faces as forms of communication, analyzing the evolutionary benefits that animals might gain from being sensitive to facial expressions. Lorenz also extended Darwin’s analysis by considering why humans are attracted to some animal faces and not to others.

  He concluded that our affinity for the faces of human babies could mislead us when we viewed animals. We see baby-faced animals as “lovable,” even if the animals’ true characters are decidedly not cuddly. Lorenz believed that large eyes, rounded features, proportionally large heads, and short limbs all release in us an instinct to embrace and to pet. Misplaced feelings also apply to other facial types. Camels hold their noses above the level of their eyes, causing us to view them as haughty and disdainful. Eagles have resolute brow ridges and mouths set in narrow, determined lines; we see in their faces leadership, imperialism, and war.

  Lorenz’s view was that our perceptions of animals are strongly discolored by the rules that we use to judge human faces. I suspect that he was right, but only partly so. Humans have interacted with animals for millions of years. Surely we might have picked up the ability to see that a raccoon isn’t a baby? This ability would have served us well. Any ancestor who could correctly interpret the danger or utility of other animal species presumably had an advantage over those with no zoological acumen. I suspect that our unconscious reactions to animals are shaped by these judgments as much as they are by misapplication of rules evolved for human faces. We have an affinity for animals that pose little physical danger to us: those with small bodies, delicate jaws, and averted, submissive eyes. We fear those whose eyes stare us down, whose faces bulge with jaw muscles, and whose limbs could outrun and overpower us. Domestication is the latest chapter of our long evolutionary relationship with other animals. Those humans who could work effectively with animal partners gained hunting dogs, goats for meat and milk, and oxen for labor. Agrarianism requires a sophisticated ability to read other animals.

  When the raccoons ambled into view, my ancestors called to me through the evolved intricacies of my brain: “Short legs and delicate jaws, squat bodies; these fellows pose little risk. The body looks well muscled, a decent meal; they show no fear, perhaps it would be fun to keep one; charming faces, like little babies.” All this wells up wordlessly from the past and suffuses me with an attraction to the animals. Later, the words try to explain the longing, but the process of attraction happens first entirely below the level of reason, layered under words and language.

  Perhaps I should not have felt so embarrassed at my immediate and strong attraction. What I interpreted as the humiliation of my pretensions as a zoological sophisticate was in fact an education in my own animal nature. Homo sapiens is a face-reading species. We ride waves of emotional judgment all our lives, drawing rapid, unconscious conclusions every time we see a face. The raccoons’ faces gave me a psychologically incongruous shock, waking my conscious mind into discomfiture. But my reaction to the raccoons was just an extension of the responses that I experience dozens or hundreds of times each day.

  As the raccoons walk away, crunching over the dry litter, I sense that my observation of the forest has held up a mirror to my own nature, a mirror that is less clouded here than in the synthetic modern world. My ancestors lived in community with animals of forests and grasslands for hundreds of thousands of years. As in all other species, my brain and my psychological affinities have been built by these millennia of ecological interactions. Human culture now modifies, blends, and transforms my mental predispositions, but it does not replace them. By my returning to the forest, albeit as an observer rather than a full participant in the community, my psychological inheritance starts to reveal itself.

  November 5th—Light

  The sound of my footsteps has changed radically this week. Two days ago, the forest floor was deep with sun-dried fallen leaves. Silent movement was impossible; walking was like traversing a field of balled crinkle-wrap. Today, the crash and crunch of autumn’s shed leaves are gone. Rain has relaxed the leaves’ tense curls, and animals move across the wetted, muted ground with silent steps.

  The rain followed a weeklong dry spell, so the moisture-loving animals of the leaf litter are moving to the surface after many days of hiding. The most striking of these small animals is a slug that glides over a patch of emerald moss. Although I have seen th
ese slugs in other parts of the forest, this is my first glimpse of one in the mandala and my first view of one traveling exposed in the midafternoon. Unlike the European slugs that plague gardens in our region, this species is a native and lives only in its aboriginal forest habitat.

  The familiar European slug has a saddle mounted on its back, just behind the head. This smooth patch of skin is the mantle that covers the lungs and reproductive organs. The native slug in the mandala belongs to the Philomycid family, all members of which have distinctive mantles that stretch the entire length of the back, like the icing on a pastry éclair. Philomycids therefore look more decently attired than their European cousins that have an unpleasant naked aspect. The expanded mantle also provides a canvas for beautiful markings. The slug in the mandala has a matte silvery ground color with dark chocolate decorations—a thin line scribed along the center of the back and fingers reaching from the mantle’s edge to the midline.

  On the rain-freshened green moss, the slug’s markings are striking and richly contrasted. As the slug slides onto the lichen-covered rock face, the effect changes. Color and form melt into the variegated surface; beauty remains, but it is the camouflaged beauty of belonging.

  My focus on the slug is interrupted by the sound of heavy rain against the tree canopy. Distractedly, I pull on my rain jacket, keeping my eye on the slug. But I was fooled: there is no rain, just pelting falls of wind-thrown leaves. The squall of leaves settles, adding another stratum to the thickening bed over the mandala. Most of this bed was deposited in the last couple of days, the leaves’ tenacious hold on their twigs broken by the extra weight of moisture from the rain. Two days ago, the forest canopy was thickly metaled with the bronze and gold of hickory and maple leaves. Today, a few sparse scraps hold out, but the canopy’s armor is gone.

  Finally, rain comes, starting with big, cold, splatting drops and settling into an even shower. More leaves descend. A tree frog rasps loudly from an oak trunk, greeting the rain with four bursts of song. Crickets fall silent. The slug continues its exploration, at home in the slick air.