Natural Community Systems -- Photo Guide

Low-gradient silty-sandy riverbank system

low-gradient silty-sandy riverbank system along the Blackwater River in Salisbury (photo by Ben Kimball for the NH Natural Heritage Bureau)
low-gradient silty-sandy riverbank system 
along the Blackwater River in Salisbury 
(photo by Ben Kimball) 


Description:  This system corresponds to sandy or silty river channels and riverbanks along low gradient, low to moderate energy, meandering sections of large streams and minor rivers.  Sandy or silty channel bars are occasional, but gravel and cobble bars are relatively rare or absent in this depositional environment.  Aquatic bed and emergent marsh communities are common, whereas these are typically absent or not well developed in higher energy settings of moderate- and high-gradient sections of river.  These communities are typically indicated by a higher density of vegetation and emergent marsh forbs, including species absent from high-energy environments.  Typically, this system has a high diversity of species.

Shrubbier portions of this system are characterized by alder, dogwoods, and Viburnums, and sometimes a diverse assemblage of other shrubs.  Adjacent floodplains typically have red or silver maple floodplain forest communities, but examples of this system may lack well-developed wooded floodplain forests.  Instead they may have extensive alluvial alder floodplains along large streams that are flooded at least annually, or they may transition rapidly to upland.

Diagnostic natural communities:

River channels and low riverbanks

   • Cobble - sand river channel (S3S4)

   • Mesic herbaceous river channel (S4)

   • Twisted sedge low riverbank (S3S4)


   • 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)

Emergent marshes and aquatic beds

   • Short graminoid - forb meadow marsh/mudflat (S4)

   • Emergent marsh (S5) 

   • Cattail marsh (S4)

   • Aquatic bed (S4S5)

Landscape settings: river channels and riverbanks (below the bankful flood-stage level) along low gradient sections of rivers and large streams (with or without well developed adjacent floodplain)

Soils: primarily alluvial sands, loams, and silt loams; moderately minerotrophic

Spatial pattern: extensive narrow-linear patches (several meters wide and miles long); linear zones parallel to river or patchy zonation corresponding to intermittent bar deposits

Physiognomy: tall shrub, medium-height shrub, herbaceous emergent, sparsely vegetated, aquatic

Distribution: broadly distributed throughout the state

Characteristic species:
   Herbaceous river channel and riverbank communities:
      Poa spp. (blue-grasses)
      Agrostis spp. (bent grasses)
      Calamagrostis canadensis (bluejoint)
      Panicum spp. (panic grasses)
      Carex torta (twisted sedge)
      Apocynum sibiricum (prairie dogbane)
      Aster spp. (asters)
      Solidago spp. (goldenrods)
      Polygonum spp. (smartweeds)
      Eupatorium spp. (Joe-Pye weeds)
      Hieracium spp. (hawkweeds)
      Equisetum arvense (field horsetail)
      Glyceria and Puccinellia spp. (mannagrasses)
      Leersia spp. (cut-grasses)
      Juncus spp. (rushes)
      Eleocharis spp. (spike-rushes)
      Carex lupulina (hop sedge)
      Carex crinita (drooping sedge)
      Scirpus torreyi (Torrey’s threesquare)
      Scirpus smithii (Smith’s bulrush)
      Scirpus cyperinus (woolly bulrush)
      Bulbostylis capillaris (hair sedge)
      Cicuta spp. (water-hemlocks)
      Sium suave (water parsnip)
      Impatiens capensis (spotted touch-me-not)
      Thelypteris palustris (marsh fern)
      Onoclea sensibilis (sensitive fern)
      Osmunda cinnamomea (cinnamon fern)
      Triadenum virginicum (marsh St. John’s-wort)
      Bidens spp. (sticktights)
      Lycopus uniflorus (common water horehound)
      Iris versicolor (northern blue flag)
      Lysimachia terrestris (swamp candles)

   Shrub and vines of riverbank and river channel communities:
      Alnus incana ssp. rugosa (speckled alder)
      Alnus serrulata (smooth alder)
      Cornus spp. (dogwoods)
      Viburnum spp. (viburnums)
      Clematis virginiana (virgin's bower)
      Spiraea alba (eastern meadowsweet)

Associated natural community systems:  This system is most often associated with temperate minor river and major river silver maple floodplain systems, and (rarely) montane/near boreal floodplains that occur on large streams.

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