Natural Community Systems -- Photo Guide

Temperate minor river floodplain system

Temperate minor river floodplain system along the Lamprey River (photo by Ben Kimball for the NH Natural Heritage Bureau)
Temperate minor river floodplain system along the Lamprey River (photo by Ben Kimball) 


Description:  This system corresponds to hardwood-dominated floodplains in central and southern New Hampshire along large streams and minor rivers, including the tributaries of the Merrimack and Connecticut Rivers and rivers in the Piscataqua and Ossipee River watersheds.  It is indicated by the dominance of red maple floodplain forests and occasionally other types (e.g. sycamore, swamp white oak, and balsam fir), often in a mosaic with oxbow marshes, vernal pools, and floodplain meadows and thickets.  Silver maple floodplain forests may form a narrow border or small patches but do not dominate extensive areas as they do along the main-stems of major rivers.  Canopies of these forests are strongly dominated by red maple (Acer rubrum), and the understory ranges from open to viny and somewhat shrubbier than silver maple floodplains, with an abundance of ferns. 

Compared to their major river counterparts, minor river floodplains appear to have reduced flood intensity, duration, and earlier peak floods due to absence or reduced importance of mountain snow-pack meltwater.  This system includes swamp white oak and basswood - white ash - black maple dominated floodplain forests restricted to silty alluvial and marine sediments in the coastal region.  Low, medium, and high floodplain variants are distinguishable in many occurrences, which correspond to slightly different elevations and thus flood return intervals.  These are marked by corresponding shifts in abundance of species preferential to wetter or drier conditions.  Invasive plants are problematic in many examples of this system, particularly Asian bittersweet (Celastrus orbiculatus) and Japanese barberry (Berberis thunbergii).

Diagnostic natural communities:

Floodplain forests

   • Red maple floodplain forest (S2S3)

   • Silver maple - false nettle - sensitive fern floodplain forest (S2)

   • Balsam fir floodplain/silt plain (S2)

   • Sycamore floodplain forest (S1)

   • Swamp white oak floodplain forest (S1)

Herbaceous and shrub floodplain communities

   • Herbaceous riverbank/floodplain (S2S4)

   • Bluejoint - goldenrod - virgin’s bower riverbank/floodplain (S3S4)

   • Alder alluvial shrubland (S3)

   • Alder - dogwood - arrowwood alluvial thicket (S4)

   • Meadowsweet alluvial thicket (S3S4)

   • Buttonbush shrubland (S4)

Landscape settings: floodplains (above bankful) along moderate-gradient and low-gradient sections of minor rivers and large streams

Soils: sandy to silty alluvium (loamy sand, sandy loam, silt loams); moderately to strongly minerotrophic

Spatial pattern: large patch, extensive broad-linear (< 1–50+ acres); meandering linear and semi-circular zones parallel to riverbanks or corresponding to floodplain terracing and oxbow, slough, or over-flow channel formations

Physiognomy: forest, woodland, sparse woodland, tall to medium-height shrub, herbaceous, and aquatic

Distribution: found along major streams and minor rivers throughout central and southern NH

Characteristic species:
Floodplain forest communities:
      Acer rubrum (red maple)

      Occasional to locally abundant:
      Prunus serotina (black cherry)
      Carya ovata (shagbark hickory)
      Quercus rubra (red oak)
      Quercus bicolor (swamp white oak)
      Fraxinus americana (white ash)
      Tilia americana (basswood)

      Carpinus caroliniana (musclewood)
      Ilex verticillata (winterberry)
      Viburnum spp. (viburnums)
      Vaccinium corymbosum (highbush blueberry)
      Cornus amomum (silky dogwood)
      Toxicodendron radicans (poison ivy)

      Onoclea sensibilis (sensitive fern)
      Osmunda regalis (royal fern)

      Athyrium filix-femina (northern lady fern)
      Boehmeria cylindrica (false nettle)
      Impatiens capensis (spotted touch-me-not)

Common species of shrub and herbaceous floodplain communities:
      Alnus incana ssp. rugosa (speckled alder)
      Cornus sericea (red osier dogwood)
      Salix sericea (silky willow)
      Clematis virginiana (virgin's bower)
      Spiraea alba (eastern meadowsweet)
      Cephalanthus occidentalis (buttonbush)

      Calamagrostis canadensis (bluejoint)
      Solidago rugosa (rough goldenrod)
      Solidago gigantea (giant goldenrod)
      Onoclea sensibilis (sensitive fern)
      Euthamia graminifolia (flat-topped goldenrod)
      Aster umbellatus (flat-topped white aster)
      Carex vesicaria (inflated sedge)
      Carex stricta (tussock sedge)
      Carex crinita (drooping sedge)
      Carex lupulina (hop sedge)

Associated natural community systems:  This system frequently occurs in association with low-gradient silty-sandy riverbank systems and less commonly with moderate-gradient sandy-cobbly riverbank systems.

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