Serpentine Barrens are a unique and rare ecosystem that only occurs in a few locations in the United States. Long ago, serpentine barrens existed all along the East Coast, from New York to Alabama, but now, much of this ecosystem has been reduced to a few fragmented preserves. A few of these preserves are located along the Maryland-Pennsylvania State Border. These remaining barrens are known as the State Line Serpentine Barrens.
Serpentine barrens were largely maintained by fires used by First Nations people for hunting. Fire and grazing by mega-fauna suppressed tree growth, allowing grasslands to flourish instead. Sadly, since European settlement, land conversion and the loss of disturbance regimes have significantly reduced the extent of serpentine barrens.
Serpentine Barrens at Nottingham County Park in Chester County. Photo from Uncovering Pa.com.
Serpentine barrens have nutrient-poor soils laden with toxic heavy metals that are too stressful for many species to exist there. Yet, some species have managed to adapt. Serpentine barrens are home to unique animals and rare plants that have become endemic to such environments. For example, Nottingham Barrens in Chester County has “29 rare plant and 38 rare animal species,” according to the Western Pennsylvania Conservancy. Sadly, because serpentine habitat is so limited, rare species have the potential to become endangered if more habitat is lost.
Many rare and endemic species in the State Line Serpentine Barrens are Laedoptira. This butterfly is the juniper hairstreak (Callophrys gryneus).
Serpentine soils are unique. The bedrock is made of ultramafic peridotite rock from which green serpentinite is derived. Weathered serpentinite creates a soil matrix high in heavy metals but low in essential plant nutrients. High concentrations of metals, like iron and cobalt, alter plant growth and metabolism. High amounts of magnesium prevent vital calcium uptake by plants. These conditions create low-fertility soils.
Low plant productivity leads to soils with low organic material input. As organic matter is the substrate for decomposition and nutrient recycling, few nutrients get returned to the earth. Soils are thin and rocky. These soils have elevated temperatures due to high exposure to the sun. This makes the soil dry; limited water availability is another stress in this environment.
The characteristic blue-gray-green color of serpentinite - a rock derived from ultramafic bedrock that is responsible for the unique rocky soils found in the State Line Serpentine Barrens. Photo from United States Department of Agriculture and U.S. Forestry Service.
While soil conditions are difficult for most plant life, serpentine species have evolved clever adaptations. Some plants can tolerate heavy metals by excluding nickel uptake from roots. Mycorrhizal fungi associated with plant roots can help plants uptake nutrients in exchange for carbohydrates from the host plant. Other plants may hyperaccumulate heavy metals in leaf tissue; plants selectively compartmentalize the metals so the metals will not interfere with the rest of the plant. Plants have adapted calcium selectivity in a calcium-poor environment. As an adaptation to limit wind exposure, plants can concentrate their leaves at the base to form a basal rosette.
An example of a plant (Eriogonum libertini) with a basal rosette morphology. Photo from United States Department of Agriculture and U.S. Forestry Service.
Serpentine plant communities exist as a patchwork of woodlands (made of pitch pines, cedar, and Virginia pine), scrublands, and grasslands. Many serpentine species are dwarfed or stunted plants due to the soil's toxicity and nutrient deficiencies. This low-lying vegetation exposes plants to high light and high-wind conditions.
While the pictures above have trees and shrubs interspersed through the grasslands, notice the open and high-light conditions the barrens maintain.
While Pennsylvania's serpentine barrens are protected, these ecosystems are threatened by human activities. Encroachment of trees from surrounding areas (an effect of land conversion into a more developed and fragmented environment) into these open spaces poses the greatest threat. Without fire and grazing disturbance, the succession of the barrens is altered and transitioned into a tree and shrub-dominated landscape. As a result, a dense canopy layer would lead to low-light conditions that serpentine plants are not adapted for.
Researchers discovered that serpentine grasslands have greater diversity than surrounding woodlands. The loss of native savanna habitat to an encroaching tree line will lead to the loss of endemic and rare species. Invasive species out-compete native ones for space and habitat as well. Mining and waste also degrade this sensitive ecosystem.
Pictured above is the serpentine aster (Symphyotricum depauperatum). This flower is "an endemic plant to the serpentine barrens of Pennsylvania and Maryland and is one of Pennsylvania’s rarest and globally significant plants" - Western Pennsylvania Conservancy
Management can protect serpentine barrens. Prescribed fires, used at the Goat Hill preserve in Chester County, help suppress the succession of native grasslands into other ecosystem types. Inventories of the species living there can direct conservation efforts and policy.
You can visit the State Line Serpentine Barrens in Lancaster, Delaware, and Chester Counties. Nottingham Park, Chrome, and Rock Springs are local preserves where you can see these stunning ecosystems yourself. You can also volunteer with Friends of Serpentine Barrens to help conserve these vulnerable ecosystems (https://the2nomads.org/FriendsWebSite/index.html).
Serpentine Barren in Nottingham County Park, Chester County.