Forest Notes: New Hampshire Wetlands: Key to Climate Resilience, Threatened by Human Activity

This article was originally published in the summer 2024 issue of Forest Notes magazine.

Among popular images of New Hampshire’s natural environment, the tall peaks and vast forests enjoy pride of place. Our many lakes, rivers, and streams are similarly treasured, some lending their names to entire regions: the Connecticut River Valley, the Lakes Region. But New Hampshire is home to subtle landscapes as well as the grand ones. 

Many are complex, shaped not only by the forces of nature, but also by the impact of human activity and the interplay between the two. Broadly known as wetlands, New Hampshire’s fens, bogs, swamps, and marshes are sometimes complicated to define, and yet they knit together land and water to create unique habitat every bit as essential to the wholeness of our landscape as our charismatic mountains, lakes, forests, and rivers.

The New Hampshire Department of Environmental Services (DES) defines wetlands as “an area that, either through surface water or groundwater, is wet enough and wet for a long enough period of time to support a predominance of vegetation that grows in saturated soil conditions.” 

The number of wetlands in New Hampshire and the total land area they represent are hard to quantify. The U.S. Fish & Wildlife Service and DES both use remote imaging technologies to try to accurately identify and measure the state’s wetlands. Documenting the many small wetlands, inherently dynamic in size and shape and frequently obscured by vegetative cover, is a particular challenge. 

While the parameters for what constitutes a New Hampshire wetland are general, the descriptions of fens, bogs, swamps, and marshes are detailed and precise. Each type has its own physical characteristics. There can be some overlap between wetland types and over time one sort may evolve into another. But the key hallmarks of each wetland type are determined by the sources of the water that feed a particular wetland, the quality and composition of that water, the species of plants that thrive in a particular wetland, and the rate at which dead plant materials in a particular wetland collect and decompose. 

Fens and Bogs

Fens and bogs frequently are discussed together. Both produce peat, and the soil and water in fens and bogs is acidic and oxygen-poor. As a result, dead plant materials that become submerged in fens and bogs do not decompose readily. In fact, plant materials accumulate more quickly than they deteriorate. This is how peat is formed. Over time, in a process called lake-fill peatland formation, enough peat may accumulate to fill the basin in which water had collected to become the bog or fen. Both readily support mosses of the genus Sphagnum, but it is the other plants that thrive in them that distinguish bogs from fens. 

Bogs are home to dwarf heath shrubs such as cranberries, blueberries, crowberries, leatherleaf, and a few sedges. Fens tend to support growth of taller signature species, including sweet gale and meadowsweet. Sedges are more abundant in fens, and other plants that are absent in bogs—Saint John’s-wort, cinnamon fern, and in some rich fens, orchids—are common in fens. 

In addition to the plant communities that each support, fens and bogs are also distinguished by the source of their water. For example, the Natural Heritage Bureau of the New Hampshire Division of Forests & Lands notes that while both are peatlands, “Bogs receive very little surface water…” while “Fens are… associated with moving water...” In New Hampshire, fens and bogs are often classified as open wetlands as opposed to swamps, which are characterized as forested wetlands. 

Swamps 

While open wetlands support low-growing plant communities and shrub vegetation, swamps, which also support these, have significant tree coverage, too. Like fens and bogs, swamps form in stagnant basins. Since they have soils that are acidic and low in nutrients, organic material from plants that grow in them can accumulate and produce peat. But because these plants are growing in the shade, the makeup of those plant communities differs from those of fens and bogs. 

The dominant species of trees found in swamps at various locations in the state vary as do the shrubs and herbs that develop beneath them, though winterberry and highbush blueberry are common in swamps statewide. 

The 2025 New Hampshire Wildlife Action Plan divides forested wetlands into two broad categories: northern swamps and temperate swamps. Northern swamps are most common from the White Mountains north and, at higher altitudes, in the southwestern part of the state. Most often developing around black or red spruce trees, these swamps are frequently surrounded by bogs or fens and may be in the final step of their development from open to forested wetland. Examples can be found at Cape Horn State Forest in Northumberland and Brown Ash Swamp in Thornton. 

The dominant tree in the temperate swamps, found primarily in southern and central parts of the state, is the red maple. The soils and waters in temperate swamps are often less acidic than those found in northern swamps and a larger portion of the water flowing into them is likely to come from streams and even small rivers. This in turn impacts the species found in them. Examples of temperate swamps can be found at Canterbury Shaker Village and within the watershed of the Contoocook River in Peterborough. 

Marshes 

Marshes are the fourth type of wetland that is common in New Hampshire. With extensive shrub and herbal vegetation, water and saturated soils, but no trees, they are visually reminiscent of fens and bogs. The most common in New Hampshire are drainage marshes found in relatively flat locations where nearby streams, ponds, and other water bodies regularly flood, bringing them nutrient rich water and causing the water level in them to fluctuate. 

Two other types, sand plain basin marshes and sandy pond shore marshes, also occur in the state. All three types provide the conditions required for plant materials to decompose. But because the water levels in them fluctuate seasonally, those materials are exposed to oxygen as they deteriorate. This allows them to release nutrients and produce muck rather than peat. Not surprisingly, peat moss, which is a signature species in bogs, fens, and swamps, is not found in most marshes. 

Many marshes are associated with bogs, fens, streams, rivers, and lakes. One location where a number can be seen is the Connecticut Lakes Natural Area in Pittsburg. They can also be found along the Pine River in the Heath Pond Bog Natural Area in Effingham. Heath Pond Bog is also one of the few designated Natural National Landmarks in the state. 

Four Centuries of Survival

Most of the bogs, fens, swamps, and marshes found across New Hampshire today are the survivors of the four centuries during which the landscape of New England has been reshaped since the first colonists encountered it. Early European settlers in the region found established and productive but almost entirely abandoned agricultural lands as they moved inland from the coast. These did not resemble the fields they had left behind in England and Holland and they set out to remake them so that they would. An important step in many locations was to shape fields to accommodate the agricultural practices and products they knew best. This included draining wetlands, which were frequently viewed as wastelands. While the exact number is not known, it has been estimated that today’s wetlands represent fewer than half of those that were here when the colonists arrived. 

The attitude toward wetlands as useless and disposable land persisted through the period when the state’s natural resources were exploited extensively to accommodate a rapidly growing population and fuel economic expansion. As is well known, beginning in the colonial period and continuing through the nineteenth century, New Hampshire’s landscapes were cleared of timber for lumber and fuel and significant expanses were opened for large scale farming. 

Prevailing attitudes toward wetlands in that period are captured by R. L. Allen in his The American Farm Book, published in 1849. There he writes: “Swamps and Peat beds occur frequently in a hilly country. These are low, level, wet lands, whose constant saturation with water, prevents their cultivation with any useful plant.” 

Early efforts to dry out damp spots would have relied on small open ditches. Subsurface drains fashioned from lumber, stones, or bricks were relied on to dry out larger areas. It is reported that the first use of clay tiles to drain land in New Hampshire was in 1854 on a farm in Exeter. When wetlands were drained, the waters that had saturated them for centuries were collected, channeled, and directed away, revealing fertile soils rich in organic materials.

In New Hampshire, farmers continued to drain and work agricultural lands that remained productive. But as the advantages of land in the Midwest drew development there, areas in New Hampshire were left fallow and, by the early years of the twentieth century, forests began to grow back across much of the state. It seems likely that in some locations, especially where woodlands reestablished themselves, wetlands may have done so as well. It is not known whether any may have been purposely restored. If so, and if it had involved the removal of networks of drainage tiles, it would have been a costly process requiring excavation.

Wetlands at Risk

In parts of the state where the population continues to grow and previously undeveloped or incompletely developed land is being suburbanized, wetlands that remain are at risk. The view of them as a wasteland is now captured in the perception that any land that remains unbuilt has not been developed to “…its highest and best use.” At the same time, a growing knowledge of natural systems, a heightened awareness of interdependencies between the different elements that comprise them, and the emergence of environmentalism have led to a deep appreciation for wetlands.

For some, this appreciation is driven by the beauty they find in landscapes nature has composed of water, land, and varied forms of vegetation. The importance of these landscapes for the survival of environmental diversity concerns others. New Hampshire’s current list of Species of Greatest Conservation Need includes animals whose survival depends on wetland landscapes. Rusty blackbirds nest in spruce fir trees found adjacent to peatlands; the northern bog lemming feeds on sedges that grow in fens; black gum swamps are home to spotted turtles; and the rare Hessel’s hairstreak butterfly spends most of its life in the canopy of Atlantic white cedar swamps. Marshes that serve a large and highly diverse environmental community provide critical stopping points for migrating birds. 

Especially powerful in an era in which the extensive impacts of climate change have grown so apparent is the growing awareness of the valuable environmental services wetlands provide. High among these is the ability of wetlands to buffer the impacts of more frequent and severe extreme weather events and the flooding they cause. Wetlands’ ability to absorb sudden surges of water and filter and release it over time has proved invaluable. It is now also understood that water they absorb and clean can move below the surface, raising the water table, and, in some instances, emerge as ground water to augment the flow of streams and rivers and even temper them to the benefit of species that live and reproduce in them. 

Research on the reproductive success of native brook trout in Coos County has shown that they seek out spots in streams where the ground water that travels underground from nearby wetlands moderates temperatures, creating areas that are cooler in the summer and warmer in the winter. Finally, at a time when the negative impacts of atmospheric pollution—especially that of large quantities of CO2—has captured the attention of policymakers, the extraordinary ability of peat formed in bogs, fens, and swamps to sequester that gas has turned the long-lived characterization of wetlands as wastelands on its head.

Dennis McFadden lives in Sugar Hill, N.H. He is particularly interested in insights the arts and humanities provide into our attitudes toward the more-than-human world.

A Note on Sources: The author wishes to acknowledge his debt to Dan Sperduto and Ben Kimball for their masterful The Nature of New Hampshire: Natural Communities of the Granite State (University of New Hampshire Press, 2011), a source he frequently consulted while researching New Hampshire’s extraordinary wetlands.