The Floodplain Forest

For inquiries contact Karen Searcy

The Southern New England Floodplain Forest is found along the rivers in Southern New England where there is periodic flooding. Photo: Flood plain forest under water in the spring. It is one of the natural communities in Massachusetts with a high priority for protection. Flooding usually occurs in the spring, but depending on the elevation above the river, can occur at other times of year as well.

Photo: Large ice blocks scouring the trees along the river's edge in winter.

After a flood, you can often see silt several feet above the ground still clinging to the bark of the trees. In fact, the lower trunk of many of the trees has been buried by silt so that trees in the floodplain lack the flaring base typical of most trees. Photo: The floodplain forest is dominated by trees such as Photo: Silver Maple,(Acer saccharinum)and Cottonwoods (Populus deltoides) which are adapted to water logging and burial. These trees can send out new roots from the buried trunk into the soil just below the surface where oxygen is higher.

Photo: New roots developed from the buried trunk of a Silver maple. Bank erosion has exposed this new root system.

Other common trees of the floodplain forest include Sycamore (Platanus occidentalis), American and Slippery elm (Ulmus americana and U. rubra), and Photo: box elder (Acer negundo).

In addition to the species of trees, floodplain forests differ from other forested areas of New England in several ways. First, there is an absence of woody shrubs. Photo: Instead, there is a dense understory of herbaceous plants. These plants die back to the ground each winter or re-establish from seed. In the summer, plants in the herbaceous layer grow rapidly and can reach six feet tall. Common species in the regularly flooded Massachusetts stretch of the Connecticut River include False nettle (Boehmeria cylindrica), Stinging nettle (Urtica gracilis), Poison ivy (Toxicodendron radicans), and Wood nettle (Laportea canadensis). Large colonies of Ostrich fern (Matteuccia struthiopteris)and sensitive fern (Onoclea sensibilis) are also common. Where flooding is a little less frequent you can find plants of Giant Ragweed (Ambrosia trifida) and Wild rye (Elymus riparius). Another factor which gives the floodplain forest an unusual aspect is the many vines which festoon the trees. In addition to grape (Vitis spp.) common vines include Clematis sp., Bur cucumber (Sicyos angulatus) and Wild Balsam-apple (Echinocystis lobata).

On the building banks and in areas with sand bars or sandy beaches with natural levees you can see how the floodplain forest develops. First, Black willow (Salix nigra) or occasionally cottonwood, which have light wind blown seeds germinate and establish in the moist open areas. Later Silver maple which is more shade tolerant establishes under the cottonwoods. Silver maple gradually shades out the willow and cottonwood and high light requiring herbaceous plants. In some places the cottonwoods will persist as linear groups marking the position of the old bank after the more shade tolerant Silver maples invade. Where the banks are steep and the river is cutting into well established floodplain forest, Silver maple comes to the edge of and in many cases over hangs the river.

Photos courtesy of Paul J. Godfrey, Ecologist, Biology Department, University of Massachusetts

You may also contact the UMASS Herbarium for help in identification.

If you want more information about this habitat, the following two references are useful:

Jorgensen, N. 1978. A Sierra Club Naturalist's Guide to
Southern New England. The Sierra Club, San Fancisco, CA.

Metzler, K. J. and Damman, A. W. H. 1985. Vegetation patterns
in the Connecticut River floodplain in relation to frequency and
duration of flooding. Naturaliste Can. 112: 535-547.