New Hampshire

A Question of Flow

The Conservancy's Christian Marks prepares to take measurements in a floodplain forest near the Ashuelot River in southwestern New Hampshire. Better understanding of the Connecticut River watershed's floodplain forests will help restore natural processes -- like high water events. Minor changes to water management regimes -- while still protecting life property -- can yield benefits for nature and people.
A Question of Flow for Floodplain Forests

Framed by enormous, towering silver maples, Christian Marks walks waist-deep in ferns, spreading out a foot of yellow measuring tape with each step.

He's in a wide, open forest in Swanzey, New Hampshire, near the muddy banks of the meandering Ashuelot River. With his other two crew members, Christian prepares to take detailed measurements of the trees and vegetation along the tape.

This is a floodplain forest, and a great example indeed. As far as natural communities go, floodplain forests are rare and getting rarer. They occur in low, flood-prone areas, sometimes near ox-bows. During periodic flooding, their soils are replenished with nutrient-rich silt,helping the growth of silver maples and other trees.

These are also strikingly beautiful forests, with big trees, wide open understories, and huge ferns galore. Rare or uncommon wildlife species are drawn to these forests, like leopard frogs, American woodcock, and red-shouldered hawk.

But as the name implies, floodplain forests need periodic flooding. Without these high-water events, the forests that have evolved here over time become dry and the species in them change with more invasive species and more upland species dominating the forests.

"Floodplain forests are an important biological community and we know very little about them,"said Kimberly Lutz, director of The Nature Conservancy's Connecticut River Program.

We know that dams and other alterations of river flow can harm floodplain forests. We know that they are threatened by conversion to development and agriculture. And we know that floodplain forests can actually help alleviate floods' damaging effects on communities by holding high water and easing the impact.

But we know little about their dynamics -- like the volume, duration and timing of high-water events that enables them to survive. There have been studies of trees and other plant life in floodplain forests. And there have been other studies of elevational profiles and flow modeling. But there have been no studies that combine the two in a comprehensive way.

That's where the Conservancy's study comes in. Christian Marks and his crew are leading an ambitious field study of floodplain forests throughout the entire Connecticut River watershed, looking at the effects of flow and elevation on trees and other flora.

The team is part-way through the first field season, visiting more than 75 floodplain dorests in Massachusetts, New Hampshire and Vermont. But already, they've found evidence that the difference of even a couple of inches in elevation can have a dramatic impact on what tree species are found there.

The study itself is part of the Sustainable Rivers Project, a partnership of the Conservancy and the U.S. Army Corps of Engineers, which owns and operates 14 dams in the Connecticut River basin. The Army Corps' mandate is flood-control, and both partners' top priority is keeping people and property safe from the effects of floods.

There may be ways to make minor adjustments in the dams' water release regimes -- including timing, volume and duration -- to make a big difference for floodplain forests. Such changes, for instance, could help seed dispersal and germination and combat invasive plant species.

"This is about restoring natural processes," said Kim Lutz. "And it can have big benefits for nature and people."