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Over the years, New Hampshire’s floodplain forests have been cleared for development due to their proximity to river systems, and plowed under for agriculture due to their rich and productive soils. Intact floodplain forests contain uncommon plants and animals and are important reservoirs of New Hampshire’s biodiversity.

Floodplain forests usually occur in the low, flood-prone areas along rivers, typically less than 20 feet above the river channel. They are often associated with oxbows (pools that have become separated from the river channel), temporary wetlands that dry up in summer (vernal pools), open meadows of grasses and wildflowers, and dense shrub thickets. The periodic floods in these forests recycle sediment and nutrients, creating some of New Hampshire’s richest soil deposits.

Why are Floodplain Forests Important?
Types of Floodplain Forests
Threats to Floodplain Habitats

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 forreptiles 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.

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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.