Floodplain forests – Intriguing, essential ecosystems

A satellite view of the Connecticut River following the floods of Hurricane Irene in 2011 shows how much sediment this mighty river carries and redistributes. Intact floodplains, including forests, protect life, property, and water quality. NASA EARTH OBSERVATORY

A satellite view of the Connecticut River following the floods of Hurricane Irene in 2011 shows how much sediment this mighty river carries and redistributes. Intact floodplains, including forests, protect life, property, and water quality. NASA EARTH OBSERVATORY

By Elizabeth Farnsworth Gazette Contributing Writer

Published in print: Saturday, March 16, 2013

When I lived in Holyoke many years ago, I always looked forward to the spectacle of the thawing ice on the Connecticut River each spring. When ice broke up and northern snows melted with the warming weather in March and April, a torrent of water would make its way downstream, transforming the normally placid Connecticut into a rowdy, roiling flood. Exciting? Absolutely. Scary? Floods certainly can be, but these annual deluges, known as freshets, were usually nicely contained, even as the river poured over its banks. That’s because the shoreline was graced — and braced — by a hardy floodplain forest.

Floodplains are changeable, rough-and-tumble places by nature; rivers course across them and back again. The painter Thomas Cole, founder of the famous Hudson River School of landscape artists, portrayed the Connecticut River outside of Northampton in 1836, when it was still just making a sharp bend. Nearly two centuries later, that bend has become our landmark oxbow, ringed by its own narrow fringe of floodplain forest.

Our house in Holyoke overlooked a lush grove of floodplain sycamores, silver maples and cottonwoods that somehow hold their own even when knee-deep in rushing water. These trees withstand periods of flooding and water-logged soil by relying on specialized adaptations: growing new roots especially adept at harvesting oxygen and producing a hormone (ethylene) that causes roots to become “spongy” so they can absorb oxygen more effectively. They are truly majestic trees, with girths of 3 feet and more. They grow so big because they occupy such rich, moist soils: silts, clays and sands that are regularly replenished and remixed by the flooding river itself.

When a freshet recedes, the forest floor comes alive, abounding with many plants valuable for food, medicine and habitat. Because it’s hard for shrubs to get a foothold and endure seasonal floods, the forest has a park-like quality, with massive trees towering over a verdant bloom of herbs. Locally, ostrich fern, source of our delectable fiddleheads, unfurls in early spring. On smaller rivers, such as the Green, the air smells deliciously of wild, oniony ramps. In summer, stinging nettles may hamper your ramble through the forest, but their leaves can provide a healthful tea. Their cousins, the false nettles, also crowd the understory—and, yes, watch out for poison ivy seedlings. Some special plant rarities may also appear. Green dragon (Arisaema dracontium) looks like a Jack-in-the-Pulpit on steroids. Winged monkey-flower (Mimulus alatus) bears whimsical, face-like flowers with a purplish blush. And two robust species of sedge (Carex typhina and Carex grayi) with big, inflated fruits, make their appearance in late summer.

The floodplain forest is also home to some special animals. Listen for the melodies of yellow-throated and warbling vireos. Peer overhead, and you may glimpse a bald eagle; they often nest in prime real estate on the shore of floodplain forests, with — literally — “killer” views of the river that allow them to spot fish and other prey easily.

Look underfoot for spadefoot toads, four-toed salamanders and wood turtles, which inhabit the ephemeral pools in swales left by the meandering river. Because floodplain forests cleanse the river of sediments and afford shade and coarse woody debris, they create habitat for downstream creatures who need clean, clear water for habitat, including dragonflies, mussels and juvenile fish.

Of course, the same fertile soils that underlie these unique habitats have also been very attractive to farmers throughout the ages. As a result, the Connecticut River valley is today a patchwork of cornfields, tobacco farms, and other agriculture, and most of the pre-colonial floodplain forests have been supplanted by crops, housing and industry.

When floodplain forests are felled, the river spreads unimpeded over flatlands, and deposits soil but also erodes banks and takes precious land and nutrients with it.

In contrast, intact floodplain forests calm the river current, dampening the flood and retaining sediments that would otherwise wash downstream. We clear these forests at our peril.

Freshets are a regular rite of spring. Recently, however, we denizens of the Pioneer Valley have witnessed some truly scary floods, dwarfing in magnitude the regular March floods that rejuvenate the floodplain. Satellite imagery of the Connecticut River shows the murky plume of muds unleashed by the floods attending Hurricane Irene, hemorrhaging out into Long Island Sound. Without floodplain forests to trap some of these sediments, the loss of precious soils would have been much worse. Despite our best-laid plans to engineer and rip-rap rivers, the waters will tirelessly seek their floodplain.

Whither will the river go now? Only time, floods, and forests — and our own land-use practices — will tell.

Elizabeth Farnsworth, co-author with John and Wendy Sinton of “The Connecticut River Boating Guide: Source To Sea” (Third Edition, Globe Pequot Press), has braved many potential cases of poison ivy to explore her favorite floodplains on foot or by kayak.

There are some lovely walks through floodplain forests in the Pioneer Valley. Take a hike along the Fern or River trails of the Arcadia Wildlife Sanctuary (127 Combs Road, Easthampton), managed by the Massachusetts Audubon Society. Or, visit one of the largest intact floodplain forests in the Commonwealth at the Fannie Stebbins National Wildlife Refuge in Longmeadow.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.

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