October 16, 2000

The autumn foliage season is upon us. Trees blaze red, orange, yellow. Others, such as oaks, turn brown. Their leaves flutter down, first one at a time, then in flurries, with each tree following its own schedule. When winter comes, these leaves will be pressed flat beneath the snow, like sodden, brown pages. Then, during summer's warmth, the microbes will eat them, releasing gases to the atmosphere, fiber to the topsoil, and nutrients back to the next crop of leaves. And so it will go on, year after year.

Now imagine that autumn's leaves didn't decompose. Imagine them accumulating year by year, layer by layer. Were this the case, our familiar world, now so rich in minerals - soil, clay, sand, sidewalks, stones, and bricks - would disappear beneath a shroud of organic matter.

This actually happened, at least locally, beneath Horsebarn Hill on the Storrs campus. Low down on its western flank is a wet meadow now carpeted by coarse brown grass and reeds. Many of us have seen this spot while driving southward into Storrs along Route 195, but seldom does it command our attention; instead we look at the gracefully curved, cow-studded pasture above and beyond it.

But this mundane meadow is - or recently was - growing upward against the flank of Horsebarn Hill, essentially smothering its base with peat. Before being timbered and drained for agriculture by English colonists, this place was first open water, then a marsh, then a red maple swamp fringed by alder, blotched by tea-colored pools of stagnant water, and tufted with sedge and grass.

My students and I have studied the natural history of this place through its pollen and decayed plant remains, and have radiocarbon-date d its sediment layers. We know that during the last eight millennia, this bottomland had risen upward more than 20 feet. That's 0.03 inches per year, which is fast by geologic standards, and an Olympic pace when compared to other wetlands around the globe.

We know, too, that during New England's early Archaic period - about 9,000 years ago - Native Americans would have viewed an isolated pond fringed by water lilies, one likely containing fish, waterfowl, and beaver.

About 6,000 years ago, however, the pond filled with sediment. Water trickling downhill from the surrounding slopes gathered in the meadow, flowing southward over a hidden groundwater spillway, producing a marsh not unlike a miniature Everglades in Florida. The water table began to rise and trees invaded the marsh, transforming the bottomland into a swamp.

Five thousand years ago, autumn foliage seasons were similar to those of today; crisp and brilliant with color. Maple leaves, identical to their modern counterparts, fluttered down in flurries. But in this epoch, the leaves from Horsebarn Hill - then totally forested - landed in a place too wet and too poorly oxygenated for microbes to do their job. As a result, a surplus of in-falling leaves and other organic matter began to accumulate.

The surplus, when pressed into peat, rose upward like a giant sponge, bringing the water table up with it, and entombing all manner of fossils into this wet, black underworld. In northern Europe at this time, the bodies of iron-age people can be found in such places, their skin tanned to leather by prolonged exposure to the peaty acids. Indeed, there is a chance that someone, or something, is preserved in the peat below Horsebarn Hill, buried by fallen foliage.

Robert Thorson