by Allison De Jong
It’s time for Field Notes, brought to you by the Montana Natural History Center.
Squoosh. Squoosh. My feet, encased in calf-high rubber boots, sank into the thick sphagnum moss, and water crept up to my ankles. I pulled one foot free with a loud squelch, lunged towards the nearest hummock, then rescued my other foot. The hummock was just big enough for me to balance on, and the water lapped the toes of my boots.
I was spending the day in a fen in the Swan Valley with a dozen fellow naturalists, learning about the flora and fauna of these unique ecosystems. From my mostly secure perch, I watched the rest of the group make their way across the fen, their movements cautious yet erratic. The surface undulated beneath their feet, as though it were an enormous waterbed—which wasn’t so far from the truth. The fen’s surface was not solid ground. What looked like solid ground was actually a thick layer of peat resting on the water beneath. In some places the layer was thinner; in some, non-existent, where the wide discs of lilypad leaves floated on the surface of the open water.
Peatlands, a general term that includes fens and bogs, are places where peat has accumulated to a thickness of at least twelve inches. Peat consists of partially decayed plant material. For peat to form, an area needs to be wet to the point of saturation throughout the year. In these waterlogged places, decomposition is anaerobic (without oxygen), and thus slower than it would be if the decomposition were aerobic (with oxygen). The cooler temperatures in prime peat ecosystems also slow decomposition. The organic plant matter accumulates at a faster rate than it decomposes, and the peat layer gradually thickens. In western Montana, peatlands deepen by one to two inches every century.
Peatlands are home to a diversity of plants; during our explorations we observed several plant species of conservation concern in addition to the more common sedges, mosses, and forbs. That morning, when we’d stood on the moat (the firmer, less peaty ground on the edge of the fen), one of the first things I noticed was bits of white fluff scattered about: cottony seeds perched atop slim stems. This was slender cottongrass—abundant in this fen, but rare elsewhere.
Another rare species that was abundant here was the carnivorous English sundew. These plants look like something from another planet: a tiny green “paddle” covered with stiff, pinkish-red hairs, each with a miniscule glistening drop at its tip. The drops are incredibly sticky, and any insect unfortunate enough to brush against them finds itself trapped—and dissolved. Most of the sundews had some type of insect caught in their dew, and a few had even trapped unlucky dragonflies and damselflies.
Not all animal life finds fens to be unlucky places, however. The dense mat of water-saturated plants provides ideal habitat for many invertebrate species, and, on the other end of the size spectrum, large mammals such as moose, elk, and even grizzly bears have been observed in fens around western Montana. But small mammals live here, too. When I saw a pocket-sized dark form dart out of a nearby hummock, I hoped it might be a northern bog lemming, Montana’s rarest mammal, whose primary habitat is fens with thick mats of sphagnum moss. Alas, it was most likely a meadow vole, a much more common rodent, but still exciting to see scurrying through the moss.
Our shadows swung eastward and we began making our reluctant way out of the fen, stopping to admire a few final plants: the wine-red flower of a marsh cinquefoil; the white flowering stalk of a hooded lady’s-tresses orchid; and one more carnivorous plant, greater bladderwort, which has an underwater bladder that opens inward when triggered by small organisms, then quickly snaps closed.
At the edge of the fen, I looked out over the vivid green carpet of plant life rooted in this floating mat of decaying plants, thinking how well it hid its secrets, how like a normal meadow it looked. I jiggled the peat mat beneath me one last time before stepping onto firm ground. Squoosh. Squoosh.
I’m Allison De Jong for Field Notes, brought to you by the Montana Natural History Center, providing natural history education for schools and the public throughout Montana. For information about upcoming events and programs at the Center, call 406.327.0405 or visit our website at MontanaNaturalist.org.
