Fen ways

Our most ecologically rich and globally significant habitats in the Northwest Corner are fens and calcareous seepage wetlands. These are wetlands of remarkable rarity and importance for conserving regional biodiversity.

Fens, like bogs, are moist peat lands where oxygen-deprived conditions prevent decay, sometimes creating a perched mat of vegetation that quakes underfoot.  They tend toward pH readings in the alkaline spectrum and are dominated by sedges.  

While bogs rely largely on surface water and precipitation, groundwater hydrology maintains a fen. Seeps and springs providing nutrient poor, calcium rich groundwater create ideal conditions for many regionally restricted plants and animals which prefer these habitats.

The marble valleys and limestone bedrock geology of our region are unique in the rest of New England. Glacial scouring left kettle holes and lake beds that slowly filled with peat to create basin fens. Sloping fens may occur where two layers of bedrock, one more porous than the other, allow groundwater to break surface, while vast areas of gravel upslope - the shorelines of glacial lakes —  provide a steady supply of spring water even in times of drought.

Since European settlement, the seepage wetlands of our region have been managed for wet pasture and woodlots.  With the extirpation of beaver and the widespread clearing of land for agriculture in the early 1800s, there may well have been more open fen habitat in that period than exists today.

Since the return of the beaver and the abandonment of farmland, our seepage wetlands have relatively little early successional habitat and may require active management to maintain their open, sedge-dominated condition.

There are all sorts of fascinating plants and animals in our fens and calcareous seepage swamps including but not limited to the rare bog turtle. Carnivorous pitcher plants and sundews may occur on open sedge mats, while bog ants make black mounds among the tussocks.  

Calcareous sloping fens may host a wide range of species, including small yellow and showy lady slippers. They are also good places to encounter poison sumac, which I can attest itches just as bad as poison ivy and seems to be the thing one always grasps for a handhold when negotiating through a fen.  

Rare northern spring amphipods and a host of uncommon or threatened waterfowl may occur in these wetlands. Many of the plants found in fens are rare and vulnerable to collection; hence an understandable reluctance of conservation entities to provide specific locations and public access to these places.

Because they are out of the public eye, fens are not always a community’s first conservation priority. State wildlife agencies or The Nature Conservancy may be able to conserve core fen habitat, but the wider basin of groundwater influence and adjacent human land use can have far-reaching impacts on these rare natural communities.  

Invasive exotic plant species often thrive in calcium rich systems, and many fens and seepage swamps are under intense threat from Phragmites, reed canary crass, purple loosestrife, buckthorn, and rosa multiflora just to name a few species.  Prescribed fire may have a limited role to play in maintaining open fen habitat but it is very difficult — and here I speak from firsthand experience —  to achieve good burning conditions and comply with wetland and rare species regulations in these systems.

In the Berkshire and Litchfield Hills, our calcareous fens and seepage swamps are among our most significant natural resources, providing habitat for some of our rarest species and emblematic of our region’s biodiversity. The first step in their protection is to recognize what we have.

Tim Abbott is program director of Housatonic Valley Association’s Litchfield Hills Greenprint. His blog is at greensleeves.typepad.com.