Highbush blueberry - winterberry shrub thicket (S4)
Highbush blueberry - winterberry shrub thickets are common and widespread in central and southern parts of New Hampshire. They occur along the upland margins of streamside marshes, and surround or fill basins in sand plain and glacial till settings that lack or have restricted outlets. Highbush blueberry (Vaccinium corymbosum) and winterberry (Ilex verticillata) form tall, dense thickets, sometimes with a low abundance of other shrub species and red maple (Acer rubrum) saplings. Herbs are usually scarce, but may include cinnamon and royal ferns.
Peat mosses and other plants abundant in peatlands are noticeably scarce or absent, distinguishing this shrub thicket community from similar peatland communities such as highbush blueberry - mountain holly wooded fen and winterberry - cinnamon fern wooded fen. In contrast to those other tall shrub peatland types, this community lacks deep peat soils, abundant peat mosses, and prominent medium-height heath shrub layers and other peatland indicators such as black spruce (Picea mariana) and pitcher-plant (Sarracenia purpurea).
Soils are mostly mineral, and vary in organic content. In some settings, leaf litter covers the soil surface and bryophytes and herbs are in low abundance. In other settings this community can grade into tall shrub fens with organic soils.
Characteristic vegetation: Dominant shrubs include winterberry and/or highbush blueberry. Seedling and sapling sized red maple are often present. Herbs are typically scarce but may include cinnamon fern (Osmunda cinnamomea), royal fern (Osmunda regalis), marsh fern (Thelypteris palustris), common water horehound (Lycopus uniflorus), and a few others. Somewhat more minerotrophic examples may contain willows (Salix spp.), alders (Alnus spp.), witherod (Viburnum nudum), and buttonbush (Cephalanthus occidentalis) in low to moderate abundance (never dominant). Dominance by buttonbush indicates the seasonally to semi-permanently flooded buttonbush shrubland community.
Variants: Two variants are described:
1. Typic variant:
This variant is characterized by a very high frequency and abundance of rhodora (Rhododendron canadense) and Sphagnum russowii with little or no highbush blueberry (Vaccinium corymbosum). The most frequent tall shrub species are mountain holly (Nemopanthus mucronatus) and witherod (Viburnum nudum var. cassinoides). Peat is moderately well decomposed within 0.25 m of the surface. Other hummock Sphagnum mosses include S. capillifolium and S. fuscum. Sphagnum russowii is occasional but more frequent than in the next variant, and S. angustifolium is occasional to sometimes abundant.
2. Dense sand plain basin marsh variant:
This variant occurs in more nutrient-poor settings such as around the margins of sand plain marshes in closed-basins. Male berry (Lyonia ligustrina), leatherleaf (Chamaedaphne calyculata), mountain holly (Nemopanthus mucronatus), red chokeberry (Aronia arbutifolia), black chokeberry (A. melanocarpa), and rhodora (Rhododendron canadense) are characteristic of this variant.
A good example of the typic variant occurs at the Hopkinton-Everett Lakes Flood Control Area (Weare).
A good example of the dense sand plain basin marsh variant occurs at Grassy Pond (Litchfield).
Highbush blueberry - winterberry shrub thickets often occur as part of larger temperate peat swamp systems, temperate minerotrophic swamp systems, sand plain basin marsh systems, and emergent marsh - shrub swamp systems, and they sometimes occur as part of coastal conifer peat swamp systems.
Highbush blueberry - winterberry shrub thicket
(photo by Dan Sperduto)