Habitat description
Riparian and floodplains habitat includes forested wetlands along rivers and streams in areas that flood seasonally or during large precipitation events. It also includes a variety of more open habitats associated with riverbanks and adjacent floodplain. Flooding, often in spring, creates important temporary habitat, transports nutrients into the floodplain, and provides a host of benefits for aquatic and terrestrial communities. These areas then dry out during the growing season facilitating plant growth and habitat use by terrestrial biota. This flooding process is critical to the river ecosystem and the surrounding riparian habitats.
Characteristic natural communities
Riparian and floodplains habitat includes several floodplain forest natural communities with variable vegetation influenced by factors including distance from the river, river/stream size, and frequency/severity of flooding. Riparian and floodplains also include more open natural communities such as rivershore meadows and several riverbank communities.
Learn more about the natural communities found in riparian and floodplains:
- Cobble bar forest (S2)
- High-energy rivershore meadow (S2)
- High-terrace floodplain forest (S2)
- Major-river floodplain forest (S2)
- Small-river floodplain forest (S2)
- Riverside seep community (S2)
- Transitional floodplain forest (S2)
- Alluvial hardwood flat community (S3)
- Alluvial red maple swamp (S3)
- High-energy riverbank community (S3)
- Riverside rock outcrop community (S3)
- Low-energy riverbank community (S4)
- Riverine pointbar and beach (S4)
- River and lake drawdown community (not ranked)
Natural communities are given state rarity/imperilment ranks ranging from S1-S5 (S1: rarest/most imperiled)
Characteristic plants and animals
Depending on the setting, silver maple, red maple, ashes, elms, cottonwood, and American sycamore may be common in floodplain forests. Sugar maple, hickories, box elder, swamp white oak and ironwood may also be present. Understory plants include spicebush, arrowwood, ostrich fern, jack in the pulpit and wood nettle. A variety of rare plants occur in Massachusetts floodplains and their rich alluvial soils green dragon, foxtail sedge, hairy wild rye, Andrews' bottle gentian, winged monkey-flower, great blue lobelia and narrow-leaved spring beauty. Floodplains provide important habitat for many rare and common wildlife species, including pumpkinseed, northern leopard frog, pickerel frog, wood turtle, ribbon snake, American bittern, marsh wren, mink, otter, and moose.
View a complete list of Species of Greatest Conservation Need associated with this habitat.
Associated habitats
Riparian and floodplain habitat is often associated with upland forest habitats such as northern hardwood and conifer forests or oak forests and woodlands. Many other habitats may occur in association with riparian and floodplain, including vernal pools, forest swamps and seeps, shrub swamps, and other wetland habitats. Riparian corridors may provide important linkages between habitat blocks across the landscape.
Ecological processes
Periodic flooding, and the associated transport of sediment and nutrients, is the primary ecological process associated with riparian and floodplain habitat. Flooding and fluctuating groundwater levels help to maintain wetlands that vary in persistence from ephemeral to permanent, mostly dependent on bank height above normal flow, floodplain soil type, and topography. Flood energy scours and deposits sediments that result in soils along a gradient of leaf litter cover dependent on position in the floodplain. Sediments provide important nutrients that would not be in the floodplain otherwise and increase productivity in these habitats. Periodic flooding influences tree and other plant composition by limiting the distribution of plants that cannot tolerate flooding.
Threats
Development and roads in floodplains and adjacent areas within the watershed can result in direct habitat loss and changes in water quality (pollution) and water quantity (natural system modification). For example, urbanization leads to increased runoff during storm events as impervious surfaces cannot retain water. In some cases water withdrawals for irrigation or consumption can also alter these systems. Dams and other structures associated with energy production can substantially alter riparian systems, interfering with sediment transport and changing flooding regimes. Prime lands for agriculture are often located in floodplains, resulting in past conversion and other potential impacts. Invasive species of plants can be a significant threat, sometimes dramatically altering the vegetation.
Climate change: Floodplain communities are influenced by the frequency, duration, and magnitude of inundation and scour associated with floods. Warming temperatures and shifting precipitation patterns have altered flood cycles in Massachusetts with more rain in winter and spring but less in summer and fall. The changes result in higher peak flows earlier in the spring and more frequent droughts into the fall. For riparian-forest habitats, this is likely to result in increased evapotranspiration rate in response to the higher temperatures and lower water flow. Higher rates of evapotranspiration may cause a drawdown of the groundwater table and may change the plant-community structure. Climate change in Massachusetts is also predicted to result in higher precipitation rates. Over time the herbaceous layer in floodplains may become sparse, as plants are more likely to be displaced by scour during intensified spring floods and as soil becomes drier during extended warming periods.
Conservation actions
- Proactive habitat protection: Protect land in and surrounding riparian and floodplain habitat, prioritizing sites supporting state-listed animals and other SGCN, as well as other wetland protection priorities identified in BioMap and other conservation planning tools (e.g., municipal open space plans).
- Habitat restoration and management: See recommendations below.
- Law and policy: Regulate and limit the impacts of development, pollutants, water withdrawals, and dams.
- Conservation planning: Include key riparian and floodplain habitats in conservation planning efforts at multiple spatial scales, including the use of riparian corridors to maintain landscape connectivity. (See BioMap as an example.)
- Public outreach: Include information about the role riparian and floodplain habitats play in biodiversity conservation, flood mitigation, water filtering, and climate resiliency as part of broader communication strategies.
Restoration & management recommendations
Dam removal: Large projects like dam removal or mimicking natural flow regimes through strategic dam water releases can be used to maintain or restore natural processes like seasonal flooding. Dam removal also improves habitat connectivity and allows for critical downstream transport of sediment. Floodplain and point-bar development can be significantly impeded by dams and regulated flows.
Water quality restoration: A variety of techniques can be used to reduce the transport of pollutants, including nutrients such as phosphorus and nitrogen, in surface flow and groundwater. These include septic system improvements, improved stormwater management, and agricultural best practices to reduce erosion and runoff.
Floodplain restoration: Re-establishment of native floodplain vegetation at highly disturbed sites can be accomplished through invasive species control, and in some cases active revegetation. On lands managed by MassWildlife and other land conservation partners, reintroduction of rare plant and animal species in appropriate habitats could be considered.
Channel and shoreline restoration: Directly removing hard structures (e.g, roads, parking lots, hardened riverbanks etc.) can increase aquatic habitat and connectivity between rivers and streams and their floodplains. Straightened and diverted channels can also be reconnected to ancestral channels to promote natural river meandering and flow regimes supporting floodplain habitats.
Invasive plant control: Control of invasive species can be completed through direct removal and long-term management. For example, Japanese knotweed and its relatives pose a significant threat to riparian habitats. The best way to avoid invasive plant spread is to avoid vegetation clearing and disturbance. Many other invasive species are found in riparian areas, and careful planning should be undertaken, including establishing realistic goals before implementing management, to ensure long-term success.