Natural Community Systems -- Photo Guide

Patterned fen system

patterned fen system near Umbagog Lake (photo by Dan Sperduto for the NH Natural Heritage Bureau)
patterned fen system near Umbagog Lake (photo by Dan Sperduto)


Description:  Slow groundwater movement through broad gently sloped peatlands forms a series of linear hummock ridges, called strings, separated by parallel hollows known as flarks.  Strings and flarks are arranged perpendicularly to the flow of water through the peatland and can form a regular pattern of parallel ridges and hollows or an intricate, braided or branching (anastamosing) pattern.  Acidic patterned fens occur where groundwater seepage is nutrient-poor.  Patterned peatlands reach their southern extent in New Hampshire where patterning is less well developed than further north; they are more extensive and well-developed in boreal and subpolar areas where precipitation greatly exceeds evaporation.

The strings and flarks in these patterned peatlands have dramatically different vegetation.  The strings in acidic examples are similar to poor level fen/bog vegetation and primarily composed of dwarf shrub vegetation, dominated by leather-leaf, other dwarf shrubs, and scattered, stunted black spruce and eastern larch.  Herbs are sparse on these hummock ridges.  Hollows are filled with open pools, liverwort/horned bladderwort mud-bottoms, or Sphagnum moss carpets with sparse dwarf shrubs and sundews.  The rare Carex exilis (meagre sedge) is a diagnostic herb of flarks in New Hampshire patterned fens.

The strings in our one circumneutral example are primarily dominated by stunted (and heavily browsed) northern white cedar, averaging 1 m tall amidst dwarf shrubs, with a taller scattered canopy of northern white cedar, black spruce, eastern larch, and red maple.  Herbs are scattered in low abundance.  All of this is over a diverse carpet of peat mosses and “brown” mosses (mostly in Amblestigeacae family). The circumneutral flarks range from a few meters to more than 10 m wide and have a thick mat of brown algae interspersed with low plant cover of herbs and mosses.

While the distinct vegetative differences between acidic and circumneutral examples could support splitting this system into two types, we consider them together as one type for purely pragmatic conservation reasons: there are so few examples, all have high conservation value, and none are likely to be overlooked in conservation efforts.

Diagnostic natural communities: 


      • Liverwort/horned bladderwort fen (S3)

      • Sphagnum rubellum - small cranberry moss carpet (S3)

      • Large cranberry - short sedge moss lawn (S3) (S. cuspidatum variant)

      • Circumneutral - calcareous flark (S1) (circumneutral examples)


      • Leatherleaf - black spruce bog (S3)

      • Northern white cedar circumneutral string (S1)

Hydrogeomorphic categories: palustrine, depressional, gently sloping, peatland,

Landscape settings: extensive flats (peatland and lowland spruce - fir forest/swamps)

Soils: moderately well to well decomposed peat; weakly minerotrophic (acidic examples) to strongly minerotrophic (circumneutral to alkaline examples); pHs 45 (acidic examples); 6.38.0 (circumneutral to alkaline examples); soligenous with some topogenous influence

Spatial pattern: small to large patch (1550+ ac); oblong to broad ovals; repeating parallel (or anastamosing) zonation of strings (hummock ridges) and flarks (hollows)

Physiognomy: dwarf shrub with stunted conifers, graminoid - moss carpets

Distribution: found only in northern New Hampshire

Characteristic species:
Acidic strings:
      Picea mariana (black spruce)
      Larix laricina (eastern larch)
      Chamaedaphne calyculata (leatherleaf)
      Kalmia angustifolia (sheep laurel)
      Ledum groenlandicum (Labrador tea)

Northern white cedar circumneutral string
Thuja occidentalis (northern white cedar) -- dom.
      Picea mariana (black spruce)
      Larix laricina (eastern larch)
      Chamaedaphne calyculata (leatherleaf)
      Kalmia angustifolia (sheep laurel)
      Ledum groenlandicum (Labrador tea)
      Muhlenbergia glomerata (clustered marsh muhly)
      Trichophorum alpinum (northern cotton club rush)
      Salix pedicellaris (bog willow)

Acidic flarks:
      Cladopodiella fluitans (liverwort)
      Utricularia cornuta (horned bladderwort)
      Vaccinium oxycoccos (small cranberry)
      Drosera rotundifolia (round-leaved sundew)
      Drosera intermedia (spatulate-leaved sundew)
      Carex exilis (meagre sedge)
      Sphagnum rubellum (peat moss)
      Sphagnum cuspidatum (peat moss)

Circumneutral – calcareous flark:
Sphagnum contortum (peat moss)
      Carex exilis (meagre sedge)
      Menyanthes trifoliata (buckbean)
      Trichophorum alpinum (cotton club rush)
      Utricularia minor (small bladderwort)
      Sarracenia purpurea (pitcherplant)
      Rhynchospora alba (white beak-rush)
      Drosera intermedia (spatulate-leaved sundew)
      Carex livida (livid sedge)
      Juncus stygius var. americanus (moor rush)
      Carex tenuiflora (thin-flowered sedge)
      Muhlenbergia glomerata (clustered muhly)

Associated systemsPatterned fen systems are surrounded by black spruce peat swamp systems and lowland spruce - fir forest/swamp systems (acidic examples) and northern white cedar minerotrophic swamp systems (circumneutral examples).

back to NH Natural Community Systems list