Floodplain forests are unique because of their periodic flooding. These regular disturbances, which deposit silt and sand along the banks of waterways, help create and maintain unique communities of plants that tolerate flooding and require nutrient-rich soils. Floodplain forests contribute many free ecological services to our society: they help filter pollutants to prevent them from entering streams, improve water quality, are critical in controlling erosion, and help buffer rivers against catastrophic flooding.

Floodplain forests as wildlife habitat
Floodplains are home to a diversity of wildlife. The damp soils create rich insect and amphibian breeding habitats, and these species in turn become prey for birds such as woodcock and barred owl, for mammals such as mink and raccoon, and for reptiles such as smooth green snake and wood turtle. Research in the Connecticut River region has shown that spring flooding thaws the soils of floodplain forests earlier than soils in surrounding areas. This early thaw means that insects become available to birds (as food) earlier in floodplain forests, so birds will feed in, follow, and depend more heavily on floodplain forests than other forested habitats during the early spring migration.

Floodplain forests as corridors
Floodplains provide corridors that allow wildlife to move from one habitat to another, especially in urban areas where development has fragmented alternative travel routes for wildlife. The overhanging canopy in floodplain forests also helps maintain cool waterways in the summer, which helps species such as brook trout.

Southern New Hampshire

Along the Connecticut, Merrimack and other large rivers, floodplain forests consist of silver maple trees and a rich ground cover of wildflowers and ferns that thrive following large-scale floods that are common in these areas. Along smaller rivers in central and southern New Hampshire, floodplain forests contain mostly red maple trees, along with black ash, black cherry and ironwood growing among vernal pools, oxbows, and shrub thickets. Less common trees such as swamp white oak, sycamore, American elm, eastern cottonwood, and river birch can also be found in floodplain forests in southern New Hampshire.

Northern New Hampshire

In northern New Hampshire and in the White Mountains, floodplain forests consist mainly of sugar maple and balsam fir. Due to the steeper topography in this region, these floodplains have quicker, faster floods, so the oxbows and vernal pools which are common along southern rivers are usually absent along northern rivers.

The species listed here are closely associated with floodplain forests, but many other wildlife species will use floodplains at some time of the year for breeding or foraging. Species of conservation concern--those wildlife species identified in the NH Wildlife Action Plan as having the greatest need of conservation--appear in bold typeface with links to their species profile from the Plan.

• Focus land conservation in areas rich in existing floodplain systems, such as the Upper Ammonoosuc River (in Coos County--contains the most extensive boreal floodplain forests of balsam fir/sugar maple), the Middle Androscoggin River (in Coos County-- contains the most extensive silver maple floodplain forests in the state, and the Lamprey River (in Strafford County -- contains the most extensive minor river floodplain forests of red maple/shrubs in the state).
• Consider removing or modifying dams that alter the natural flood regimes of rivers. There are more than 5,000 dams in New Hampshire, many on private lands. If dams are removed or altered to become “run-ofriver” dams, restored natural flows can help maintain floodplain plant communities and benefit migratory birds and fish, amphibians, reptiles, and invertebrates that depend on seasonal flooding.
• Reduce recreational trails and roads within floodplain forests. These roads and trails can impede wildlife movement between wetland and upland habitats, especially during spring and early summer, when birds, amphibians and reptiles breed and young disperse from the river or nearby vernal pools into the surrounding upland areas. Trails can also provide an avenue for invasive plants to enter floodplain forests.
• Monitor healthy floodplain forests to prevent new infestations of invasive plants.
• Where feasible, consider controlling populations of invasive plants, recognizing that control will be necessary both upstream and downstream to prevent ongoing re-infestation. The New England Wildflower Society (newfs.org), UNH Cooperative Extension (extension.unh.edu) and other organizations offer training in invasive species identification and control.
• Forest management in floodplain forests should aim to regenerate existing floodplain species such as silver maple, balsam fir/sugar maple, or red maple. This may be problematic, however, if dams have altered the flood regime in a forest. Existing trees may be relics of past flood regimes, and regenerating species such as silver or red maple in the new, drier conditions may be difficult.
• Limit overstory removal of trees in floodplain areas where invasive plant species are present. Creating canopy gaps by timber harvesting can encourage invasive plant species to invade the disturbed areas; limiting the amount of light reaching the ground within floodplain forests can help discourage the establishment or spread of invasive plants.
• Always consult a licensed New Hampshire forester before conducting a timber harvest on your property. Understand and follow all laws pertaining to the harvesting of trees near wetlands and waterbodies. Follow established Best Management Practices, and harvest timber near wetlands only when the soils are either frozen (winter) or very dry (summer).