“Ecologically, stone walls are elevated, dry, rocky, and porous volumes, surface areas, and lines within an otherwise moist woodland, providing novel habitats, exposures, boundaries, and corridors. By retaining moist sediment, the uphill side of this wall supports luxuriant ferns in the background. The drier downhill side supports grass and herbs in the foreground. Holyoke State Forest, Massachusetts.”
Historically, the inland wetlands of New England were critical to indigenous lifeways. To the European settlers, however, they were generally seen as nuisances on the landscape: obstacles to transportation, sources of disease, and wild lands waiting to be redeemed by drainage and clearing. During the 1990s, the more hidden values of inland wetlands became widely known, with a specific focus on wildlife habitat, flood mitigation, water quality, and education. Regulations soon followed, and protected wetlands are now broadly appreciated and enjoyed by the general public.
During the mid 1990s, I was heavily engaged in the investigation and management of New England’s inland wetlands as a research scientist. Simultaneously, I was working on New England’s signature landform, the iconic fieldstone walls that emerged from the region’s colonial and early American stages before widespread access to fossil fuels. The end result was up to 250,000 miles of stone walls cross-crossing rural New England. More than half of these remain, mostly in woodlands that were once field and pasture. During the last few years, I’ve paid increasingly attention to the ecological role of walls as habitats and their hydrological roles within watersheds.
During one of my recent talks –increasingly online– I began researching the parallel between wetlands and drylands. The EPA’s popular pamphlet Functions and Values of Wetlands opens with these words: “Long regarded as wastelands, wetlands are now recognized as important features in the landscape that provide numerous beneficial services for people and for fish and wildlife.” Quite suddenly, I realized that if you swapped in the word “dryland” for the word “wetland,” the sentence would still work nicely, with one exception. A dryland wall submerged by flooding would no longer be dry, but would still diversify habitat as an underwater reef. My most recent thinking on this phenomena will be published in the February 2025 (Volume 47) issue of the scholarly journal The Public Historian, which quote in the caption above and the indented text below
Like natural talus slopes or mountain scree, stone walls are dry, granular, linear, rocky landscape elements in an otherwise moister, soil-covered, vegetated landscape. The lichens, moss, and microbial mats on walls exist nowhere else except for bedrock exposures and large boulders. The higher thermal heat capacity and conductivity of stone cause walls to retain the cold of night and the warmth of day longer than the adjacent soils, creating novel ecological opportunities. During winter and summer, they conduct heat more efficiently into and out of the ground, creating seasonal bulbs of frozen ground and thawed soil. As porous volumes, walls and concentrations provide homes for creatures needing protected places. Insects, rodents, and snakes are common, and the dens of larger burrowing animals are frequently beneath basal stones. As geographic areas, walls are small, but as an aerial gridwork, they broadly pixelate the land surface. As lines, walls are borders between adjacent habitats, and corridors connecting distant habitats.
The ecological effects of walls extend well beyond the dryland edges. As stable ridges, their opposite sides are sunny vs. shaded, windward vs. leeward, and upslope vs downslope. This changes the local seasonal phenology of dry vs. wet sides, snow-covered vs. snow-free, accumulation of soil vs. erosion of soil. All of these differences greatly increase the details of habitat texture, enhancing biodiversity. A loss of walls is a loss of biodiversity.
Walls are the dryland counterpart of inland wetlands. These impermeable, exposed, ventilated habitats contrast with the saturated soils of nearby wetlands on the same land parcels. Prior to the early 1990s, and except for early ecologists and conservationists, inland wetlands were usually considered blights on the landscape. Cultural incentives and land regulations fostered destruction via drainage and filling. Only after the hidden values of wetlands were clearly connected to the lives of ordinary citizens were they protected. This same narrative applies to stone wall drylands. Prior to having their hidden values recognized, many of New England’s walls were strip-mined and crushed for road gravel, buried to enhance drainage, or quarried for fill or building stone.
Counterintuitively, stone walls and inland wetlands were often created by the same agricultural transformation. Sediment eroded from hillsides concentrated the upland stone that became walls. When deposited at lower elevation, that same sediment occluded drainages and aggraded floodplains to create and enhance many wetlands.
My fervent hope is that increased scientific and public recognition of the habitat diversification provided by New England’s signature landform will strengthen the movement to conserve as many as possible.