Wildlife


Floodplain Forest Habitats


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About Floodplain Forests in New Hampshire

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.

Oxbow aerial photo
Click on links to browse the content of this webpage:

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

Wildlife Found in Floodplain Forests
Stewardship Guidelines
Additional Resources

Why are Floodplain Forests Important?
 

floodplain forest 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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Types of floodplain forest in New Hampshire
  Merimack Silver Maple

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.

Wet Spruce forest

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Threats to Floodplain Forests
Agriculture & Development Human development of floodplain forests permanently eliminates habitat. Building and construction of paved roads may also separate wildlife populations, inhibit migration, create increased predation and promote collisions on roads. Paving areas of native floodplain forests lessens the water-storage capacity of the land, which can cause more frequent and catastrophic floods, with potentially drastic effects on wildlife, people, and communities downstream.

Agriculture also has a negative impact on floodplains, but a less permanent one than human development. Over time, agricultural fields may revert to forest, and in their current condition they provide a different kind of habitat (hayfield, cropland) used by many wildlife species.
development & floodplains
Impact of Dams Dams on rivers prevent natural flooding, permanently altering the plant and wildlife communities of floodplain forests downstream. “Run-of-river” dams, which operate using available stream flow, not by storing water behind the dam, allow for normal flow except during periods of high water. Newmarket Mills
Invasive Plants Invasive plant species spread easily in the frequent disturbances created by flooding and tend to thrive in the rich soils of floodplain forests. Particularly problematic are Oriental bittersweet, Japanese knotweed, and black swallow-wort, which can outcompete existing native vegetation, strangle trees or eliminate the tree canopy. Invasive plants may also directly impact floodplain wildlife. Research shows that berries from invasive plants such as bittersweet and buckthorn are lower in nutrition—like junk food for birds—than berries from native shrubs. (see Oriental bittersweet, at right) oriental bittersweet

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Additional Resources for Floodplain Forests

Floodplain Forests CoverClick here to download and print the Habitat Stewardship Series brochure on Floodplain Forests, containing information about recognizing floodplain forests, what the threats are to this habitat type, the wildlife found there, and what you can do to help conserve these special habitats.

Managing Riparian Forests - click this link for a UNH Cooperative Extension fact sheet

To learn more, read the NH Wildlife Action Plan habitat profile for Floodplain Forests, including information about the condition and location of this habitat, the threats facing this habitat, and conservation actions recommended by biologists to protect floodplain forests in New Hampshire.

Wildlife species found in floodplain forests
Several wildlife species of conservation concern in New Hampshire depend on floodplain forests. To learn more about each species, click on the link below to read its Wildlife Action Plan profile.

American black duck
Cerulean warbler
Eastern red bat
Jefferson salamander
Northern leopard frog
Red-shouldered hawk
Sliver-haired bat
Wood turtle

Photo Credits on this page: Ben Kimball, NH Natural Heritage Bureau, Malin Clyde, Dave Govatski

Research for this webpage and accompanying Habitat Stewardship brochures was conducted by UNH Cooperative Extension staff with support from the Sustainable Forestry Initiative and NH Fish & Game

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