Natural Community Systems -- Photo Guide

Kettle hole bog system

Kettle hole bog system at Heath Pond Bog (photo by Ben Kimball for the NH Natural Heritage Bureau)
kettle hole bog system at Heath Pond Bog (photo by Ben Kimball)

kettle hole bog system at Philbrick-Cricenti Bog (photo by Ben Kimball for the NH Natural Heritage Bureau)
kettle hole bog system at Philbrick-Cricenti Bog (photo by Ben Kimball)


DescriptionKettle hole bog systems are found where big chunks of glacial ice were stranded and partially buried in glacial outwash or other coarse ice-contact deposits.  The ice chunks subsequently melted, leaving ponds in holes in the ground, with no hydrologic inlets or outlets.  Over millennia, peat has progressively filled in the kettle holes from the edges inward toward the pond center; most still have a central bog pond with a floating mat border, while some have filled the kettles entirely with peat, obscuring the former ponds under floating or grounded peat mats.  These are oligotrophic peatlands, due both to very limited terrestrial runoff influence from their small watersheds and coarse, porous soils, and to the dominance of precipitation as the primary water source (pHs are generally 4.0 or lower).  There is often a moat or lagg separating the peat mat from the surrounding upland, which is largely a result of increased decomposition due to elevated nutrient levels from upland runoff as well as periodic, seasonal drawdown of the water table. 

The vegetation is dominated by species indicative of oligotrophic conditions including scattered, stunted black spruce, numerous dwarf heath shrubs (leatherleaf, small cranberry, sheep laurel, bog laurel), "mud-bottoms" (wet, floating lawns dominated by low, turfy mats of the leafy liverwort Cladopodiella fluitans, which turns black and looks like mud from a distance), bladderworts, and white beak-rush.  A typical community sequence from the upland border towards the center of the kettle hole is marshy moat (when present), tall shrub fen or black spruce swamp, followed by a dense leatherleaf - black spruce bog zone, then a floating, reddish-colored open moss carpet (Sphagnum rubellum) with extremely dwarfed shrubs, and patches of Sphagnum pools with Sphagnum cuspidatum and mud-bottoms.  With the exception of the zone immediately along the upland border, pHs are usually 4.0 or lower throughout the bog. 

Diagnostic natural communities:

      • Liverwort/horned bladderwort fen (S3)

      • Sphagnum rubellum - small cranberry moss carpet (S3)

      • Leatherleaf - black spruce bog (S3)

      • Highbush blueberry - mountain holly wooded fen (S3S4)

      • Marshy moat (S4)

Peripheral or occasional natural communities:

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

      • Water willow - Sphagnum fen (S3)

      • Leatherleaf - sheep laurel shrub bog (S1S3)

Landscape settings: closed-basin, kettle hole depressions in glacial outwash or ice-contact deposits

Soils: deep, poorly decomposed peat; oligotrophic; pHs <4.0; topogenous

Spatial pattern: small patch (120 acre); circular to irregular shape; more or less concentric zonation

Physiognomy: sparse woodland, tall shrub, dwarf shrub, moss carpets/lawns

Distribution: broadly distributed in New Hampshire, but concentrated in the central and southern portions of the state where kettle holes are more abundant

Characteristic species:
Indicators of oligotrophic conditions found in kettle hole and poor level fen/bog systems:
   Dwarf to short shrubs
      Chamaedaphne calyculata (leatherleaf) <20” high (max 36”)
      Kalmia angustifolia (sheep laurel)
      Kalmia polifolia (bog laurel)
      Andromeda polifolia var. glaucophylla (bog rosemary)
      Ledum groenlandicum (Labrador tea)
      Vaccinium oxycoccos (small cranberry)
      Gaylussacia baccata (black huckleberry)
      Gaylussacia dumosa (dwarf huckleberry)

Herbs and carnivorous plants
      Drosera rotundifolia (round-leaved sundew)
      Drosera intermedia (spatulate-leaved sundew)
      Sarracenia purpurea (pitcherplant)
      Eriophorum virginicum (tawny cotton-grass)
      Eriophorum vaginatum (hare's-tail)
      Carex trisperma var. billingsii (Billing's sedge)

   Trees and tall shrubs (sparse and dwarfed)
      Vaccinium corymbosum (highbush blueberry)
      Picea mariana (black spruce)

pHs generally 4.1 or lower
   Mud bottoms with mats of black liverwort

Indicators of weakly to moderately minertrophic conditions mostly absent (or limited to peatland margins) in kettle hole and poor level fen/bogs:
      Carex lasiocarpa (hairy-fruited sedge)
      Carex utriculata (bottle-shaped sedge)
      Carex stricta (tussock sedge)
      Carex lacustris (lake sedge)
      Carex canescens (silvery sedge)
      Lysimachia terrestris (swamp candles)
      Dulichium arundinaceum (three-way sedge)
      Triadenum virginicum (marsh St. John's-wort)
      Osmunda cinnamomea (cinnamon fern)

Shrubs and trees 
      Myrica gale (sweet gale)
      Spiraea alba (eastern meadowsweet)
      Spiraea tomentosa (steeple bush)
      Chamaedaphne calyculata (leatherleaf) >20” and usually closer to 36” high
      Vaccinium macrocarpon (large cranberry)
      Alnus incana ssp. rugosa (speckled alder)
      Ilex verticillata (winterberry)
      Acer rubrum (red maple)

pHs generally in low 4s to low 5s

Associated natural community systems:  Kettle hole bog systems often occur in isolation of other wetland systems.  They can also be surrounded by peat swamp systems (temperate, coastal conifer, or black spruce types) or occur adjacent to poor level fen/bog systems and, less frequently, medium level fen systems.

thin fringe of water willow - Sphagnum fen in a kettle hole bog system (photo by Ben Kimball)
thin fringe of water willow - Sphagnum fen in a kettle hole bog system (photo by Ben Kimball)

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