Dirt

Soil, which has been called the "poor man's rain forest," faces ecological pressures of its own. A spade of rich garden soil may harbor more species than the entire Amazon nurtures above ground. Two-thirds of Earth's biological diversity lives in soil and underwater sediment, a micromenagerie that includes uncataloged millions of bacteria and fungi, but also tiny nematodes, copepods, wingless insects called springtails and their better-known cousins: mites, beetles, snails, shrimp, termites, pill bugs and earthworms.
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The road twists for 26 miles across the heart of the Great Smoky Mountains National Park, climbing from Gatlinburg, TN, to Newfound Gap, where it joins the Blue Ridge Parkway in North Carolina.

It's a Saturday morning in August when I arrive with Keith Langdon, a US Park Service biologist. The parking lot is filling up, and tourists are piling out of their cars. Despite days of cleansing rains, a bright haze shrouds the woodlands where dozens of plant and animal species make their homes.

Thousands of other species-we're here to help find out how many-live close to the surface in moss, twigs and dirt; in shallow puddles and streams; and especially underground. The Cherokees called these mountains the "place of blue smoke," but the haze that covers this ancient range today is from power plants and automobile exhaust.

Ozone concentrations here are up to twice the levels of Atlanta or Knoxville because polluted air gets trapped up here with nowhere to go, and 90 plant species in the Smokies show leaf damage from excessive ozone.

In 2002, the National Parks Conservation Association declared the Smokies the nation's most polluted park. Helping to find out how this pollution affects the tiny animals that live here is also part of our mission, though it will take years to know for sure.

The menagerie underfoot
Soil, which has been called the "poor man's rain forest," faces ecological pressures of its own. A spade of rich garden soil may harbor more species than the entire Amazon nurtures above ground. Two-thirds of Earth's biological diversity lives in soil and underwater sediment, a micromenagerie that includes uncataloged millions of bacteria and fungi, but also tiny nematodes, copepods, wingless insects called springtails and their better-known cousins: mites, beetles, snails, shrimp, termites, pill bugs and earthworms.

These small, mostly unknown creatures are so important to our lives that Harvard University ecologist Edward O. Wilson calls them "the little things that run the world." Collectively, they make up complex underground "food webs" that grind, shred and consume the litter that falls to earth; store and recycle nutrients vital to plant growth; generate soil; renew soil fertility; filter and purify water; degrade and detoxify pollutants; control plant pests and pathogens; and help determine the fate of carbon and greenhouse gases-and thus the state of Earth's atmosphere and climate. All of these ecological services arise from the spontaneous activities of billions of creatures going about the business of nourishing the soil and reproducing themselves-without our giving them a moment's notice.

Some of these creatures are accessible to anyone curious enough to poke through rotting leaves, backyard dirt or the mud of a marsh; most are too small to see without a microscope or magnifying glass.

By day's end, we hope to know more about the ones that live in the Great Smokies, which is reputed to harbor the richest array of plant and animal life in temperate North America. Seven years ago, the park became the first protected area in the world to attempt to inventory literally every species within it. By the end of 2004, more than 500 species new to science and 3,300 previously not known to have even existed here in the Smokies were discovered, including bacteria, fungi, lichens, slime molds and earthworms.

Today, hunting still more species, I'm tagging along with Langdon and his assistants. On this unlikely treasure hunt, we will sift soil, shake trees and search through litter.

Richer than the rain forrest
Walking east into the forest, we enter a narrow avenue of rhododendron bushes. Beneath them, amid damp, mossy rocks, we see ferns and tiny mushrooms. These ectomycorhizae (fungus roots) produce chanterelles, truffles and boletus mushrooms, better known to foodies as porcini.

"I've been to Costa Rica, and I would go all day hiking in the tropical rain forest and find maybe one mushroom," Langdon says as we move out onto a forested ridge, its sharp slopes obscured by lush greenery. "Here, you can stand in one place and see 20 different kinds."

How long we will be so fortunate is anybody's guess. Truffles and other prized mushrooms have been growing ever scarcer in the acid rain-drenched forests of Europe, and a similar fate may await the plant and animal life of the Great Smokies. What form this damage will take, no one knows, which is another reason this inventory is underway.

If even one of these tiny species were to disappear, it is impossible to know what the effect would be. Ecologist Paul Ehrlich has likened the myriad species on Earth to rivets in an airplane. Surely some can pop out and the plane will still fly. But lose too many, or lose a key rivet here or there, and the plane will crash. Of all the rivets holding Earth together, the ones we know least about are those underground, which makes these efforts all the more important.

On the bug trail
Shortly after we set out, our trail drops below the ridge with the north-facing slope rising steeply on our right. Langdon's assistants set to work, one whapping the branches of a cranberry bush with a stick, the other holding a "beat sheet" to catch any bugs and beetles that rain down. Then they use a rubber-tubing-and-pipe apparatus they call a pooter to suck the catch into a jar.

Langdon clambers upslope through ferns and shrubs, and begins filling zip-top bags with moist black soil, some of which will be placed in funnels with light suspended over them to motivate the tiny organisms to crawl downward and fall into waiting flasks. Other soil samples will end up in Petri dishes where colonies of slime molds will grow.

He tosses the bags down to me and works his way back to the trail. Taking a fine sieve, he pours a measured amount of soil and litter on it and shakes it vigorously, while I hold a pan underneath to catch the crumbs.

"Now we're going to look for everything that moves in here," he says, instructing me to sit with the tray in my lap. I put the pooter's rubber tubing in my mouth and hold the metal pipe over the tray.

Langdon points. "Over there, really tiny, a spider." I move the pipe end over the crawling speck, and-success!-it's in the jar. Over the next 15 minutes, I capture a few dozen more specks. Finally, when nothing else on the tray seems to be stirring, Langdon holds up a specimen vial while I tap the tiny wildlife from my jar into it. After adding alcohol, I slip in a pencil-written label with the collection date, place and, at last, my own name on it.

Out of sight, out of mind
Since the dawn of agriculture, humans have recognized the value of the soil itself but have given little thought to the multitude of creatures that live within it, enabling it to produce such bounty. Even scientists have paid so little attention to what goes on underground that, at best, only 5 percent of soil animals have been identified.

Together, however, these creatures dominate life on Earth, not just in their diversity but in their sheer body mass. The bacteria in a single acre of soil, for example, can easily outweigh a grazing cow or two-or, in the Smokies, a mother bear and her cubs.

Today, a growing cadre of scientists drawn from numerous disciplines is beginning to look at the complex ecosystems beneath our feet, eager to discover what is down there, how each contributes to the functioning of the soil, which ones are organized into communities and food webs, why some communities are richer in some species than others, and how our own activities threaten them.

But unlike Mars exploration, the effort to understand life underground is not driven just by intellectual curiosity and a sense of adventure. These scientists realize that the diversity of life in soils and sediments is under increasing threat, just like plant and animal species above ground. So, as a result, are the delicate ecological processes that sustain life for them and for us. The researchers hope they have not started too late.

Tiny contributions
"Snails are going to be at the base of trees, under moss and rocks," Langdon says, as we begin our search for larger species. "Sometimes it helps if you take your fingers and just claw gently through the leaf litter to see if anything comes out." Suddenly, he sags. "The thing is, there's so much acid rain falling at the upper elevations in these mountains that the mollusk specialists tell us not to expect the number of snails there used to be, or the variety of types," he says.

"I don't think we're going to find much here, frankly." But we do find a few, and move up the trail. Within an hour, rain is sheeting down on us, and I'm drenched. The trail becomes an ankle-deep stream as we hurry on to the shelter at Icewater Spring. The rain is warm, and I wonder what pollutants are being washed from the sky, and what effect they will have on the plants and animals that will remain in these mountains long after I'm back home, safe and dry.

I will always wonder exactly what species turned up in my search and what contribution-if any-I have made to this attempt to understand the threats these soil-dwellers face. Odds are, I will never know.

Once the specimens are sorted and sent off in different directions to be identified, the names of the humans who collected them will be long forgotten. This, perhaps, is as it should be. Science, generally, is a collective enterprise, with each individual-like the creatures we are studying-making its own tiny, and usually unheralded, contribution.