Natural Community Systems -- Photo Guide

Maritime rocky shore system

Maritime rocky shore system at the Isles of Shoals (photo by Dan Sperduto for the NH Natural Heritage Bureau)
Maritime rocky shore system at the Isles of Shoals (photo by Dan Sperduto)

DescriptionThis system occurs on the Isles of Shoals off the New Hampshire coast.  As small islands set miles off the coast into the Atlantic Ocean, they are considerably more exposed to and battered by the maritime environment than nearby mainland shore areas.  Despite a long history of human use, these islands apparently retain some substantial areas of largely natural shrub thickets, rocky barrens, and intertidal areas exposed to and shaped by wave action, tides, heavy surf, salt spray, and when the tide is drawn down, dehydrating sun and wind.  Early records indicate that these islands were probably never heavily wooded.  The interior portions of the Isles of Shoals at one time may have been somewhat more wooded and corresponded to a mosaic of maritime shrub thicket and coastal rocky headland communities.  The latter community has a woodland structure (25–65% tree cover) dominated by Juniperus virginiana (eastern red cedar) and Myrica pensylvanica (northern bayberry).  This community is otherwise restricted to some rocky estuarine points in Great Bay.  Based on an initial survey of Star Island, there are three apparently distinct natural communities that comprise the maritime rocky shore system: maritime shrub thicket, maritime rocky barrens, and intertidal rocky shores.

The maritime shrub thicket consists of short (mostly less than 1 m) to tall (mostly 1–2.5 m) shrub thickets found in interior areas away from the exposed rocky shorelines.  These thickets are dominated by shrubs and stunted trees with a lower abundance of understory herbs.  Prior to the island’s long history of human land use, the maritime thicket likely covered most of the island.

Maritime rocky barrens lie between maritime shrub thickets at higher elevations and maritime intertidal rocky shores at lower elevations.  These exposed rocky barrens have a sparse cover of herbs and even fewer shrubs that creep down from the shrub thicket above into protected crevices.  Little soil and wind-driven salt spray limit plant growth on the exposed bedrock.  Characteristic species include Solidago sempervirens (seaside goldenrod), Juncus gerardii (salt marsh rush), Festuca rubra (red fescue), Aster subulatus (small salt marsh aster), Achillea millefolium (European yarrow), Toxicodendron radicans (climbing poison ivy), and Myrica pensylvanica (northern bayberry).  Several other associated species occur with a very sparse cover.  A few small depressions within this community hold fresh to brackish water pools.  Fresh water species include Lemna minor (lesser duckweed), Polygonum hydropiper (water-pepper), Polygonum punctatum (dotted smartweed), Scutellaria galericulata (marsh skullcap), Iris versicolor (northern blue flag), Lycopus uniflorus (common water horehound), and Typha latifolia (common cattail).  Brackish water species are Scirpus pungens (three-square rush), Scirpus robustus (stout bulrush), Eleocharis halophila (salt-loving spike-rush), Potentilla egedii (coastal silverweed), Lythrum hyssopifolia (hyssop-leaved loosestrife), and Juncus gerardii (salt marsh rush).

Intertidal rocky shores are found from the supra-littoral (splash) zone down to the shore expose at low tide.  They are exposed to wave action, tides, and when the tides are drawn down, sun and wind.  These environmental factors have a strong influence on species composition and zonation.  Vascular plant species are absent.  Non-vascular species include blue-green algae and lichens in the supra-littoral and high littoral zones and several species of macroalgae in the middle and lower intertidal zones. 

Diagnostic natural communities:

      • Maritime shrub thicket (S1) 

      • Maritime rocky barren (S1)

      • Intertidal rocky shore (S3) 
      • Maritime meadow (S1) 

      • Maritime cobble beach (S1)

      • Brackish water pool (S1)

Peripheral or occasional natural communities:

      • Short graminoid - forb meadow marsh/mud flat (S4)

      • Highbush blueberry - winterberry shrub thicket (S4)

      • Coastal shoreline strand/swale (S2)

      • Coastal rocky headland (S1)

Landscape settings: offshore islands

Soils: Well to somewhat excessively well drained, thin soils over bedrock and in cracks in outcrop

Spatial pattern: small patch (<5–100+ acres); zonation parallel to shoreline

Physiognomy: shrub thickets, and sparsely vegetated rocky barrens and intertidal areas

Distribution: Isles of Shoals

Characteristic species:

Maritime shrub thicket:
Short and tall shrub thickets:
Abundant shrubs
      Myrica pensylvanica (bayberry)
      Aronia arbutifolia (red chokeberry)
      Aronia melanocarpa (black chokeberry)
      Toxicodendron radicans (poison ivy)
      Rosa virginiana (low rose)
      Amelanchier stolonifera (dwarf shadbush)

   Other occasional species
      Achillea millefolium (yarrow)
      Festuca rubra (red fescue)
      Aster novi-belgii (New York aster)
      Sedum sp. (stonecrops)
      Potentilla tridentata (three-toothed cinquefoil)
      Agrostis capillaris (Rhode Island bent-grass)
      Polygonum scandens (false buckwheat)
      Prunus maritima (beach plum)

Tall shrub thickets (additional species)
      Amelanchier canadensis (eastern shadbush)
      Parthenocissus quinquefolia (Virginia creeper)
      Rosa rugosa (rugose rose)
      Rubus allegheniensis (common blackberry)
      Rubus idaeus (red raspberry)
      Prunus serotina (black cherry)
      Acer rubrum (red maple)
      Ilex verticillata (winterberry) -- dom. in low wet swales

      Agrostis capillaris (Rhode Island bent-grass)
      Anthoxanthum odoratum (sweet vernal grass)
      Elytrigia repens (quack-grass)
      Poa pratensis (Kentucky bluegrass)
      Poa compressa (Canada bluegrass)
      Fragaria virginiana (wild strawberry)
      Smilacina stellata (starry Solomon's seal)

Maritime rocky barren:
      Solidago sempervirens (seaside goldenrod)
      Juncus gerardii (salt marsh rush)
      Festuca rubra (red fescue)
      Aster subulatus (small salt marsh aster)
      Achillea millefolium (European yarrow)
      Toxicodendron radicans (poison ivy)

   Dwarf shrubs
      Myrica pensylvanica (northern bayberry). 

Small embedded fresh to brackish water depressions:
      Lemna minor (lesser duckweed)
      Polygonum hydropiper (water-pepper)
      Polygonum punctatum (dotted smartweed)
      Scutellaria galericulata (marsh skullcap)
      Iris versicolor (northern blue flag)
      Lycopus uniflorus (common water horehound)
      Typha latifolia (common cattail)
      Scirpus pungens (three-square rush)
      Scirpus robustus (stout bulrush)
      Eleocharis halophila (salt-loving spike-rush)
      Potentilla egedii (coastal silverweed)
      Lythrum hyssopifolia (hyssop-leaved loosestrife)
      Juncus gerardii (salt marsh rush) 

Associated natural community systems: This system occurs by itself on the Isles of Shoals.

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