The Forest Unseen: A Year's Watch in Nature (2 page)

The lichens’ growth forms mountains in miniature, sandstone crags with variegated patches of moisture and sunlight. The highest ridges on the boulders are spattered with tough-skinned gray flakes. Dark canyons between rocks have a purple sheen. Turquoise glistens on vertical walls, and concentric circles of lime flow down gentle slopes. All the lichens’ hues are paint-stroke fresh. This vibrancy contrasts with the winter-weighed lethargy of the rest of the forest; even the mosses are muted and frost-bleached.

Supple physiology allows lichens to shine with life when most other creatures are locked down for the winter. Lichens master the cold months through the paradox of surrender. They burn no fuel in quest of warmth, instead letting the pace of their lives rise and fall with the thermometer. Lichens don’t cling to water as plants and animals do. A lichen body swells on damp days, then puckers as the air dries. Plants shrink back from the chill, packing up their cells until spring gradually coaxes them out. Lichen cells are light sleepers. When winter eases for a day, lichens float easily back to life.

This approach to life has been independently discovered by others. In the fourth century BCE, the Chinese Taoist philosopher Zhuangzi wrote of an old man tossed in the tumult at the base of a tall waterfall. Terrified onlookers rushed to his aid, but the man emerged unharmed and calm. When asked how he could survive this ordeal, he replied, “acquiescence… I accommodate myself to the water, not the water to me.” Lichens found this wisdom four hundred million years before the Taoists. The true masters of victory through submission in Zhuangzi’s allegory were the lichens clinging to the rock walls around the waterfall.

The quietude and outer simplicity of the lichens hides the complexity of their inner lives. Lichens are amalgams of two creatures: a fungus and either an alga or a bacterium. The fungus spreads the strands of its body over the ground and provides a welcoming bed. The alga or bacterium nestles inside these strands and uses the sun’s energy to assemble sugar and other nutritious molecules. As in any marriage, both
partners are changed by their union. The fungus body spreads out, turning itself into a structure similar to a tree leaf: a protective upper crust, a layer for the light-capturing algae, and tiny pores for breathing. The algal partner loses its cell wall, surrenders protection to the fungus, and gives up sexual activities in favor of faster but less genetically exciting self-cloning. Lichenous fungi can be grown in the lab without their partners, but these widows are malformed and sickly. Similarly, algae and bacteria from lichens can generally survive without their fungal partners, but only in a restricted range of habitats. By stripping off the bonds of individuality the lichens have produced a world-conquering union. They cover nearly ten percent of the land’s surface, especially in the treeless far north, where winter reigns for most of the year. Even here, in a tree-filled mandala in Tennessee, every rock, trunk, and twig is crusted with lichen.

Some biologists claim that the fungi are exploiters, ensnaring their algal victims. This interpretation fails to see that the lichen partners have ceased to be individuals, surrendering the possibility of drawing a line between oppressor and oppressed. Like a farmer tending her apple trees and her field of corn, a lichen is a melding of lives. Once individuality dissolves, the scorecard of victors and victims makes little sense. Is corn oppressed? Does the farmer’s dependence on corn make her a victim? These questions are premised on a separation that does not exist. The heartbeat of humans and the flowering of domesticated plants are one life. “Alone” is not an option: the farmer’s physiology is sculpted by a dependence on plants for food that dates back hundreds of millions of years to the first wormlike animals. Domesticated plants have experienced only ten thousand years of life with humans, but they too have shed their independence. Lichens add physical intimacy to this interdependence, fusing their bodies and intertwining the membranes of their cells, like cornstalks fused with the farmer, bound by evolution’s hand.

The diversity of color in the lichens on the mandala reflects the many types of algae, bacteria, and fungi involved in the lichens’ union.
Blue or purple lichens contain blue-green bacteria, the cyanobacteria. Green lichens contain algae. Fungi mix in their own colors by secreting yellow or silver sunscreen pigments. Bacteria, algae, fungi: three venerable trunks of the tree of life twining their pigmented stems.

The algae’s verdure reflects an older union. Jewels of pigment deep inside algal cells soak up the sun’s energy. Through a cascade of chemistry this energy is transmuted into the bonds that join air molecules into sugar and other foods. This sugar powers both the algal cell and its fungal bedfellow. The sun-catching pigments are kept in tiny jewel boxes, chloroplasts, each of which is enclosed in a membrane and comes with its own genetic material. The bottle-green chloroplasts are descendants of bacteria that took up residence inside algal cells one and a half billion years ago. The bacterial tenants gave up their tough outer coats, their sexuality, and their independence, just as algal cells do when they unite with fungi to make lichens. Chloroplasts are not the only bacteria living inside other creatures. All plant, animal, and fungal cells are inhabited by torpedo-shaped mitochondria that function as miniature powerhouses, burning the cells’ food to release energy. These mitochondria were also once free-living bacteria and have, like the chloroplasts, given up sex and freedom in favor of partnership.

And life’s chemical whorl, DNA, bears the marks of yet more ancient union. Our bacterial ancestors shuffled and swapped their genes among species, blending genetic instructions like cooks copying from one another’s recipe cards. Occasionally two chefs would agree to a wholesale merger, and two species fused into one. The DNA of modern organisms, including our own, retains traces of such mergers. Although our genes function as one unit, they come with two or more subtly different writing styles, vestiges of the different species that united billions of years ago. The “tree” of life is a poor metaphor. The deepest parts of our genealogies resemble networks or deltas, with much interweaving and cross flow.

We are Russian dolls, our lives made possible by other lives within us. But whereas dolls can be taken apart, our cellular and genetic helpers
cannot be separated from us, nor we from them. We are lichens on a grand scale.

Union. Fusion. The mandala’s inhabitants are plaited into winning partnerships. But cooperation is not the only relationship in the forest. Piracy and exploitation are here also. A reminder of these more painful associations lies coiled on the leaf litter at the center of the mandala, enclosed by the lichen-coated rocks.

The reminder unwrapped itself slowly, held back by the torpidity of my powers of observation. My attention was first drawn by two amber ants bustling across the wet leaf litter. I watched their scurrying for half an hour before I noticed the ants’ particular interest in a coiled strand nestled in the litter. The strand was about as long as my hand and was the same rain-soaked brown as the hickory leaf on which it lay. At first I dismissed the curl as an old vine tendril or leaf stem. But as my eyes were about to move on to more stimulating things, an ant paddled the tendril with her antennae, and the coil straightened and lurched. My mind started into recognition: a horsehair worm. A strange creature, with a taste for exploitation.

The worm’s twisting gave away its identity. Horsehair worms are pressurized from within, and the tug of muscles against this inflated body makes the worm jerk and writhe like no other animal. The worm has no need of complicated or graceful movement, for at this stage of its life it has only two tasks left, to squirm toward a mate and then to lay eggs. Nor did the worm have need of sophisticated motion in its previous life stage, when it lay balled inside the body of a cricket. The cricket did the worm’s walking and feeding. The horsehair worm lived as an internal brigand, robbing then killing the cricket.

The worm’s life cycle began when it hatched from an egg laid in a puddle or stream. The microscopic larva crawled over the streambed until it was eaten by a snail or small insect. Once inside its new home, the larva wrapped itself in a protective coat, formed a cyst, then waited.
The lives of most larvae are cut short at this point, as cysts, never completing the rest of the life cycle. The worm in the mandala was one of the few that make it to the next stage. Its host crawled onto land, died, and was chewed on by an omnivorous cricket. This is such an improbable sequence of events that the horsehair worm’s life cycle requires parent worms to lay tens of millions of eggs; on average, only one or two of this multitude of young will survive to adulthood. Once inside the cricket, the spiny-headed larval pirate bored through the gut wall and took up residence in the hold, where it grew from a comma-sized larva to a worm the length of my hand, coiling upon itself to fit within the cricket. When the worm could grow no more, it released chemicals that took over the cricket’s brain. The chemicals turned the water-fearing cricket into a suicidal diver seeking puddles or streams. As soon as the cricket hit water, the horsehair worm tensed its strong muscles, ripping through the cricket’s body wall, and twisted free, leaving the plundered vessel to sink and die.

Once free, horsehair worms have a keen appetite for company, and they mate in untidy skeins of tens or hundreds of worms. This habit has given them a second name, Gordian worms, after the eighth-century legend of King Gordius’s monstrously complex knot. Whoever could unbind the knot would succeed the king, but all would-be rulers failed. It took another pirate, Alexander the Great, to loose the knot. Like the worms, he cheated his hosts, slashing the knot with his sword and claiming the country’s crown.

After the Gordian mating tangle is sated, the worms unwrap and crawl away. They lodge their eggs in soggy pond margins and damp forest floors. Once hatched, the worm larvae will pick up the Alexandrian plunderer’s spirit, first infecting a snail, then emerging to rob a cricket.

The horsehair worm’s relationship with its hosts is entirely exploitative. Its victims receive no hidden benefit or compensation for their suffering. But even this parasitic worm is sustained by an interior crowd of mitochondria. Piracy is powered by collaboration.

·   ·   ·

Taoist union. Farmer’s dependence. Alexandrian pillage. Relationships in the mandala come in multifarious, blended hues. The line between bandit and honest citizen is not as easily drawn as it first seems. Indeed, evolution has drawn no line. All life melds plunder and solidarity. Parasitic brigands are nourished by cooperative mitochondria within. Algae suffuse emerald from ancient bacteria and surrender inside gray fungal walls. Even the chemical ground of life, DNA, is a maypole of color, a Gordian knot of relationships.

A
nkle-deep snow has smoothed the forest’s fractured, uneven surface into a gentle swell and trough. This covering disguises deep cracks between rocks and makes walking treacherous. I move slowly, bracing myself against tree trunks as I slide and clamber to the mandala. I brush the snow from my rock, then sit, huddling in my coat. Loud cracks, like gunfire, echo down the valley every ten minutes or so, the sound coming from snapping fibers in ice-stiffened branches of the bare, gray trees. The temperature has dropped to ten below, not a hard freeze but the first real cold of the year and enough to stress the trees’ wood.

The sun emerges, and snow transforms from a soft layer of white into thousands of sharp, bright points of light. I hook a fingertip of this glittering jumble from the mandala’s surface. Seen closely, the snow is a tangle of mirrored stars, each one flashing as its surface aligns with the sun and my eye. The sunlight catches the minute ornamentation of each flake, revealing perfectly symmetrical arms, needles, and hexagons. Hundreds of these exquisite ice flakes crowd onto one fingertip.

How is such beauty born?

In 1611, Johannes Kepler took time away from elucidating the motions of the planets to meditate on the snowflake. He was particularly intrigued by the regularity of snowflakes’ six sides: “There must be some definite cause why, whenever snow begins to fall, its initial formations invariably display the shape of a 6-sided starlet.” Kepler
searched for an answer in the rules of mathematics and the patterns of natural history. He noted that the honeybee and pomegranate array their combs and seeds in hexagons, perhaps reflecting geometrical efficiency. But water vapor is not squeezed into a rind like pomegranate seeds, nor is it built up by the work of insects, so Kepler believed that these living examples could not reveal the cause of the snowflakes’ architecture. Flowers and many minerals don’t conform to the six-sided rule, further frustrating Kepler’s search. Triangles, squares, and pentagons can also be stacked into neat geometrical patterns, eliminating pure geometry from the list of possibilities.

Kepler wrote that snowflakes are showing us the spirit of the earth and God, the “formative soul” that inhabits all being. But this medieval solution didn’t satisfy him. He sought a material explanation, not a finger pointing toward mystery. Kepler ended his essay in frustration, unable to peer beyond the door of the icy palace of knowledge.

His frustration could have been eased had he taken seriously the concept of the atom, an idea that originated with the classical Greek philosophers but had fallen out of favor with Kepler and most early seventeenth-century scientists. Yet the atoms’ two-thousand-year exile was coming to a close, and by the end of the seventeenth century atoms became fashionable again, balls and sticks dancing triumphant across textbooks and chalkboards. Now, we seek out atoms by blasting ice with X-rays, using the pattern of the rays that emerge to discover a world one million billion times smaller than the normal scale of human life. We find jagged lines of oxygen atoms, each atom tethered to two restless hydrogen atoms, electrons flashing. We float around the molecules, examining their regularity from all angles and, incredibly, see atoms arranged like Kepler’s pomegranate. This is where the snowflakes’ symmetry begins. Hexagonal rings of water molecules build on one another, repeating the six-sided rhythm over and over, magnifying the arrangement of oxygen atoms to a scale visible to human eyes.