NATURE’S VIEW

Left: A walking bridge is all that’s left of a trail at the Merrimack River Outdoor and Education Conservation Area after water levels rose and flooded the property temporarily. Right: Growing season is kick-started into high gear after water recedes in the floodplain and sunlight begins to bake the forest floor.

The Silver Maple Floodplain Forest

By Dave Anderson

Arare and special riverside forest community grows not far from downtown Concord on undeveloped floodplains along the Merrimack River adjacent to the Forest Society’s headquarters. Silver maple floodplain forests are unique not only for their relative scarcity, but also due to the historical development pressures and specialized plant communities and wildlife habitats that occur on the rich, silty soil deposited by annual flooding cycles.

For more than two centuries, industrial mills built dams in many New Hampshire rivers, including the Merrimack, to provide waterpower and later to control flooding. Changing the historicalfrequency and severity of spring flood events altered soil, plants, and wildlife populations. Natural flood cycles built rich alluvial soil deposits, which became the most productive sites for agriculture. Industrial and agricultural land uses altered and converted disproportionate percentages of the original riparian floodplain forests to farmlands and mills and industrial centers of growing cities.

Undeveloped floodplains often feature the former river channels that form oxbow ponds and seasonal vernal pools, which provide habitat for aquatic plants and wildlife. Wet meadows, thickets, shrubs, and silver maple forests are the original fast food “Miracle Mile,” outlying downtown and rich with protein and carbohydrate calories.

Spring and fall bird migrations tend to follow river floodplain corridors with fruit- and berry-producing shrubs. Ample fish and amphibians feed birds and small mammals which, in turn, feed larger predators and birds of prey. Waterfowl and wading birds—ducks and herons—stalk fish and amphibians. Barred owls and red-shouldered hawks often nest near floodplain wetlands. Migrating birds of floodplains include bank swallows, kingbirds, orioles and kingfishers. Fish, frogs, salamanders, snakes, and turtles breed in and near warm, shallow water. Teeming insects fuel aerial foraging by bats and birds. Mammals particularly well adapted to live along rivers and wetlands include raccoons, muskrats, beaver, mink, and otters.

At the Forest’s Society’s Conservation Center, silver maple forests narrow to an

artificial southern limit due to extensive industrial development further south from Bow and Hooksett to Manchester, Nashua, and on to Massachusetts’ Lawrence, Lowell, and Haverhill. Northward, silver maple forests stretch in a narrow belt along the meandering Merrimack River from Concord to Boscawen, Canterbury, Northfield, and Franklin. Adjacent oxbow ponds and agricultural fields on rich alluvial floodplain terraces are common sites to see on a paddle in this area. This same linear natural community occurs along the floodplains of the Connecticut and Saco rivers.

Prior to agricultural and industrial development, silver maples won by default being best adapted to sand and silt and able to tolerate late winter and early spring flooding with periodic ice jams along these major rivers.

Understory plant communities of silver maple forests include wildflowers, ferns, and poison ivy. Ostrich fern, the commercial fern fiddleheads people forage for personal consumption and found for sale in supermarkets emerge on low-lying river floodplains by early May. Invasive plants spread by birds and through flooding readily spread to outcompete native vegetation. The “three bad B’s” include patches of non-native buckthorn, Eurasian barberry, and thick coiling bittersweet vines, in addition to Japanese knotweed and honeysuckle. Rich soil and the open understory create a beachhead for aggressive plants adapted to disturbance. “A silver maple-false nettle-sensitive fern floodplain forest community occurs on sandy and acidic soils adjacent to medium and large rivers in the southern half of New Hampshire,” notes Forest Society Forester Gabe Roxby. “They are commonly found along the Merrimack River but are also present along sections of the Ashuelot and Contoocook rivers. The community is characterized by a nearly pure canopy of tall silver maple trees that arch out over the river’s edge. The understory is diverse and variable, but commonly is dominated by a mixture of both ferns and nettles. The natural community on the floodplain is closely related to the silver maple- wood nettle-ostrich fern natural community type, though, and there is likely overlap in the plant species found on each.”

Floodplain forests and wetlands provide some of the most important edible native plant resources utilized by Indigenous Abenaki peoples for thousands of years. This forest type, where it survives intact, remains little changed. Our Indigenous predecessors would not recognize most contemporary forests and land use, they but would certainly recognize a silver maple floodplain forest as familiar. Tall and straight or arching trunks of silver maples lined all the primary pre-colonial transportation corridors: major rivers analogous to modern highways. The Merrimack and Contoocook rivers were functional precursors to I-93 and I-89 for thousands of years.

Dave Anderson is the senior director of education for the Forest Society

ELLEN KENNY (X2) Get Out!

The Merrimack River Outdoor Education and Conservation Area is open every day from sunset to sundown. For more information, visit forestsociety.org/property/merrimack-river-outdoor-education-conservation-area.

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