The Missing Fens

The latest in a series on Connecticut’s 13 most imperiled ecosystems.

This story was published in the Spring 2017 issue of Connecticut Woodlands magazine. For more, please visit

I. Looking for a Fen

From a snowy gravel road on the shoulder of Canaan Mountain, in Litchfield County, the flat Housatonic Valley looks like the work of a god-sized steamroller. A geologist, however, might revere this gulf between mountains more for its tectonic masonry. This immense stretch of lowland is Robbins Swamp, the largest inland wetland in Connecticut, but it is also perhaps the finest and most opulent marble sink that has ever been crafted, cut from the bedrock of the so-called marble valleys of the state’s northwestern corner. Yet such elegant stonework does not explain the biologist who describes this region to me as “magical.”

As I admire the view, snow melting down the slopes of the surrounding mountains pours into this sink like a faucet. In the process, the waters flow and filter over the calcium-rich, or “calcareous,” bedrock on its way to the valley floor. Since the drain of this sink is clogged by thousands of years of peat accumulation, the groundwater rises. When this happens—and only this exact sequence—conditions are ripe for the creation of what has been described as the rarest habitat in North America: a small, unassuming patch of open wetland called a calcareous fen.

I’d come to glimpse this habitat before it disappeared. I would find it with the help of the Connecticut Critical Habitats Database, and also with a few tips from Kenneth Metzler, who had personally collected much of the data. Before retiring from his 30-year tenure as a botanist for the state ecological survey, Mr. Metzler authored a paper with University of Connecticut biologist Dr. David Wagner that listed calcareous fens as one of the thirteen most imperiled ecosystems in Connecticut. He’d warned me that the search would be difficult even if I knew exactly where to look. “I’m not sure what they even look like now,” he said about the fens he’d mapped within Robbins Swamp a decade ago. “Ten years, even though it doesn’t sound long, is a lot of time for the vegetation to change.”

I was far from optimistic. Wildlife directors at the Connecticut Department of Energy and Environmental Protection, which owns most of Robbins Swamp, had told me there were no intact calcareous fens there anymore. If that were the case, I wanted to see what had happened to them. It would help me understand what might become of the rest.

II. Found Only Here

In Connecticut, most fens go by the names of brooks, ponds, or swamps, to which they often bear an outward similarity. According to Dr. Erik Kiviat, a biologist and director of the Hudsonia wetlands research center, fens are characterized by low, shrubby vegetation on saturated but not flooded soils. However, unlike more typical wetlands, classification as a calcareous fen depends on two specific criteria. First, the fen must sit on an area of calcareous bedrock, such as limestone or marble, and second, the fen must be fed by groundwater from subsurface seeps or surface springs. When the groundwater flows saturate the soil, calcium from the bedrock reduces its acidity, creating a habitat of either pH-neutral or slightly alkaline wetland—a calcareous fen.

Places where this combination can occur are extremely rare. The primary limiting factor is suitable bedrock, which in the northeast is confined to a thin band of limestones and marbles called the Grenville Shelf Sequence running up the New York-New England border. Nearly all of the fens in the region occur along that line—but importantly, only where this bedrock is able to affect the chemical composition of the groundwater. Overall, such sites in Connecticut number somewhere between 10 and 15.

When geology matches hydrology, however, there are several ways that a fen can occupy a landscape, and most wetlands classification systems distinguish between multiple kinds of calcareous fens. The primary division is between “sloping fens,” or spring-fed fens occupying hillsides, and “basin fens,” which occur in saturated lowlands. Further distinctions exist between “rich” and “poor” fens, which are sometimes used to describe pH or nutrient levels, but Dr. Kiviat prefers simple terminology to describe the complexity of fen habitats. “When I go out in a field and look at a fen, at least in this region, I see a mixture of different communities,” he said. “I might see rich, medium-rich, and other stuff all mixed together.”

To the above criteria, Dr. Kiviat adds a third condition for identifying fens: vegetation. Perhaps the most important feature of fens is the habitat they provide for high numbers of rare plant species, many of which are found nowhere else—they are “faithful to fens,” as Dr. Kiviat puts it. A common method of studying fens is to measure the presence and abundance of these species, which biologists refer to as “fen indicator plants.” In Connecticut, these include a variety of sedges, notably the threatened barratt’s sedge, as well as flowering plants like spreading globeflower and the rare showy ladyslipper orchid, which was a favorite of Charles Darwin.

Like the presence of living corals in a coral reef, fen indicator plants are an indicator of the health of the fen ecosystem. By extension, their absence can signal degradation. In 2010, Dr. Kiviat published a study of fens in New York and Connecticut which selected sites based on the condition of their fen indicator plants. After narrowing his sample down to the healthiest sites available, the study included just two fens in the state of Connecticut.

III. A Habitat in Flux

The fens have existed in Connecticut since the end of the last Ice Age, but there is some debate about how they’ve remained intact through the present day. “These are not static habitats,” says Tim Abbott, Regional Land Protection and Greenprint Director at the Housatonic Valley Association. “They go through a process of natural succession.”

Succession occurs when a low, open fen is colonized by taller and denser grasses, which in turn can give way to woody plants, tall shrubs, and, eventually, timber forest. Since most fen indicator plants are fairly short, the growth of a tall canopy deprives them of sunlight, driving them out of the habitat. To prevent this, fens need someone to pull the weeds—or perhaps eat them. “What probably kept these systems open historically was mastodons,” says Mr. Abbott, “large grazers and browsers who went after the woody stuff.” Later, the fens were sometimes cleared of woody plants by Native American burning practices. Early European settlers drained many fens for crops, but remaining fens often benefitted from the presence of nearby farms. “What probably kept them open in the last 300, 400 years were a lot of cows.”

The “really awful problem,” as Mr. Abbot puts it, is that few of these disturbance sources occur in the fens today. “Most of them are on a new trajectory to a less diverse expression of a calcareous wetland complex with trees,” he says. One question researchers try to answer is how long it takes to lose an open fen to natural succession. Without disturbances like beaver, which can flood an area and revert a fen to an earlier stage, it typically takes just 15 to 25 years for succession into tall shrubland, and another 40 to 70 years for a forested swamp to predominate.

However, one study of a prehistoric fen in New York found evidence that fens have the potential to sustain themselves for thousands of years, raising the possibility that succession may not always occur. Meanwhile, Dr. Kiviat’s research suggests that one driver of rapid fen succession might be coming from modern humans. Undisturbed fens are low-nutrient environments, and most fen indicator plants have evolved to survive on relatively low levels of nutrients such as nitrogen and phosphorous. Yet these nutrients are also found in common sources of human pollution. Nitrogen, for example, is found in many fertilizers, and runoff from developed areas can deposit it into a fen. Elsewhere, through a process known as “atmospheric deposition,” phosphorous compounds emitted by Midwestern power plants arrive on westerly winds and settle in aquatic habitats on the eastern seaboard. As Dr. Kiviat explains, the introduction of these nutrients allows common plant species to move in and out-compete the fen indicator plants. “It makes the habitats better for certain things”—for instance, cattails or woody shrubs—“but worse for any of the rare species,” says Dr. Kiviat. His research has found a correlation between nitrogen levels and non-fen-specific vegetation.

The problem of invasive species, meanwhile, is unquestioningly the fault of human actions. The European variety of common reed, most often called by its Latin name phragmites, is a more robust strain of its native counterpart and grows rapidly in wetlands across the United States, including fens. Tall and dense, with thick roots, phragmites choke out virtually all other vegetation in an area when left unchecked. Other tall invasives like purple loosestrife, barberry, and shrub honeysuckle seem to spread particularly quickly in the alkaline conditions of a fen. “They just go berserk in it,” says Mr. Abbott.

Our most destructive impact on the fens, however, is likely still to come. Climate change is expected to bring both warmer and wetter conditions to the fens, which Mr. Abbott says will benefit many of the taller successional plants and invasives. And as Dr. Kiviat points out, many fen indicator plants reach the southernmost limit of their ranges in the fens of northwest Connecticut. Climate change will likely push those ranges north, removing species like the showy lady slipper out of the state for good.

IV. Endangered Gardens

Most of the remaining open fens in Connecticut today are the property of the Nature Conservancy, who began purchasing fens around the same time as Mr. Metzler and Dr. Wagner’s “Imperiled Ecosystems” study. Mr. Abbott was a director of the Conservancy’s Berkshire-Taconic Program during this period, which operated with an emphasis on preserving the matrix of calcareous wetlands in the tri-corner region of Connecticut, New York, and Massachusetts. He describes this work as a good first step, but points out that considerable management is still needed to address the present and future threats facing Connecticut’s fens.

“Your work is absolutely not done when you’ve put the ten-acre fen into conservation ownership,” says Mr. Abbott. “If what you care about is the biodiversity of that rare system—the plant and animal species that they sustain, including one federally-listed species—then there are a lot of stewardship implications.”

That federally-listed species is the bog turtle. Endemic to only two isolated regions of the eastern United States, bog turtles are so threatened that no sources for this story would confirm their present or even past locations. Small and described by Mr. Abbott as “adorable,” the turtles are coveted targets for poachers, who sell them as pets on the black market. Dr. Kiviat characterizes the practice as “elephant ivory writ small.”

In both their southeast and northeast populations, bog turtles depend on open, groundwater-fed wetlands with low vegetation for nesting sites. They also require the ability to move within a matrix of suitable habitat areas. In the northeast, those habitats are calcareous fens, which means that bog turtle populations are deeply affected by incursions of invasives and successional plants in fens over time. “They live longer, sometimes, than their habitat does,” says Mr. Abbott. Ensuring the survival of the state’s bog turtles will likely require managing the fens to protect and maintain open habitat where it still exists—again, pulling out the weeds. “You’re gardening for rare plants,” he says. “You’re gardening for bog turtle.”

But gardening in a fen is a bigger task than it might seem, and current practices to maintain the fens are limited. The Nature Conservancy actively manages phragmites on all of their fens, but David Gumbart, the land conservation director for the Conservancy’s Connecticut office, says that complete removal using herbicides is only feasible on a small scale; larger tracts are only mowed. Purple loosestrife is similarly hard to uproot, and doing so on a wide area can damage the soil; the next best thing is to merely cut the seed heads. In both cases, vegetation stature is improved for bog turtle nesting, but this comes at the expense of the rare fen plants.

There is, however, one agency in Connecticut with a mandate to protect the full suite of biodiversity in the fens. In 2015, the state Department of Energy and Environmental Protection released its updated Wildlife Action Plan, which listed calcareous fens among the ten key habitats in need of future protection. The plan announces several actions to ensure the survival of fens, including “minimize habitat degradation from nutrient concentrations,” “minimize habitat fragmentation,” and “implement wetland restoration and enhancement projects,” with the intent to implement these strategies over the next ten years. Yet with the state currently dealing with a budget shortfall, the outlook for the Wildlife Action Plan is uncertain. Bill Hyatt, head of DEEP’s Bureau of Natural Resources, informed me that due to the hiring freeze in place, positions vacated by retirements automatically disappear from the department. This applies even to positions that were created to fill a necessary role in the state’s core environmental strategy. The department’s most recent retirement, said Mr. Hyatt, was the position in charge of the phragmites control ward.

Today, a handful of fens in Connecticut remain outside of either state or Nature Conservancy protection. Another state program, the Green Plan, provides incentives for DEEP or other conservation groups to increase the amount of land under conservation ownership, but neither it nor the Wildlife Action Plan include calls to purchase unprotected fens. At Robbins Swamp, a revised management plan in 2002 lead to new parcels being added to the state’s Wildlife Management Area there. Not included were the two fens identified at Robbins Swamp by Mr. Metzler’s Connecticut Critical Habitats Database.

With the coordinates from the database in my phone, I parked at the marble quarry—Mr. Metzler’s suggested entry point—and hiked north up the railroad bordering the swamp to the latitude of the fens. When I arrived, the view was of an endless succession of trees.

I hiked in and around the forested swamp interior—technically trespassing, since this was unprotected land—but there was nothing else to see. Either the data was wrong, which did not seem likely, or the fen was no longer there. Ten years is a long time. What might the rest look like in 50?

I put the question to the man tasked with protecting most of the fens in the state of Connecticut. Mr. Gumbart’s response: “Who knows?”