About the Barrens

What is a serpentine barrens?

In the most general sense, a serpentine barrens is an area underlain by serpentine rock (or other ultramafic rocks) which supports relatively sparse vegetation compared to the surrounding area. They can range from almost completely bare rock through grassland and savannah to pine-oak forests. The difference in vegetation is often sharp and dramatic, and is caused by several factors: the very high ratio of magnesium to calcium in serpentine, which is unfavorable to plant growth, the presence of heavy metals such as nickel (and to a lesser extent cobalt and chromium), and the tendency of serpentine to fracture, forming thin, shallow mineral soils.

In the eastern United States, serpentine and related rocks occur in a discontinuous chain running along the eastern side of the Appalachian Mountains. The southernmost serpentine barrens of the chain occur at Burks Mountain, Georgia, and Buck Creek, North Carolina.  The next distinct area of barrens vegetation is Travilah Barrens, on the northern shore of the Potomac in Montgomery County, Maryland. The typical eastern serpentine barrens occur at irregular intervals between Travilah and Staten Island; while serpentine can be found to the north, running from the middle of Vermont north through Quebec and Newfoundland, the effects of glaciation and climate result in very different plant communities.

Several different vegetative communities may be present at a single serpentine barrens site. The driest, most well-drained areas will typically support an open grassland, sometimes continuous, sometimes patchy and interspersed with bare serpentine gravel. The dominant grasses are typically little bluestem (Schizachyrium scoparium), Indian grass (Sorghastrum nutans) and prairie dropseed (Sporobolus heterolepis). These grasslands are particularly prized from an ecological standpoint, as they support prairie species that are quite uncommon east of the Appalachians. Competition-intolerant plants, like the round-leaved fameflower (Phemeranthus teretifolius) and rock stitchwort (Sabulina michauxii) can be found taking refuge in the gravelly openings. On slopes and in stream valleys, where there is more moisture and the soil is deeper, large, entangling thickets of greenbrier (Smilax rotundifolia and S. glauca) form, and, if unchecked, will gradually reabsorb many grasslands. These provide habitat for the rough green snake (Opheodrys aestivus) which reaches the northern limits of its range just above the Maxon-Dixon Line. Many of the grassy openings have a savannah-like character, with scattered pitch pine (Pinus rigida), Virginia pine (Pinus virginiana), eastern red-cedar (Juniperus virginiana), and scrub oaks (Quercus marilandicaQ. prinoides, and Q. ilicifolia). As these trees drop leaves and organic matter accumulates, greenbrier thickets grow up around them; eventually, succession results in mixed forests of pine, oak, and red maple (Acer rubrum). Eastern whip-poor-wills (Antrostromus vociferus) nest in these woodlands, flying out over the grasslands at night to catch moths.

Where are the State Line serpentine barrens?

The State Line serpentine barrens are a series of grasslands over a large serpentine outcrop straddling the Pennsylvania-Maryland border in Chester and Lancaster Counties, Pennsylvania, and Cecil County, Maryland. They start in the east at Chrome Barrens, about 4 miles southeast of Oxford, Pennsylvania, and extend slightly south of west as far as the Conowingo Creek at Pilot Barrens, in Cecil County. An outlying exposure of serpentine to the north of this main belt forms the New Texas Barrens, about 3 miles north-northeast of Pilot. Collectively, they represent one of the larger intact serpentine barrens communities in the eastern US, comparable to Soldiers Delight in Baltimore County, Maryland.

Why do the serpentine barrens need care?

While the mineral soil weathered from serpentine rock is shallow and chemically poor, providing little support for most plants, as pioneer trees take hold in the grasslands, they provide shade and deposit organic matter in the soil through fallen leaves. Under these enriched conditions, less tolerant plants can begin to invade the barrens, and the process of succession eventually converts the area to a forest, albeit more slowly than on a more typical Piedmont soil. For thousands of years, this process was arrested by the regular use of fire by Native hunters, who created wide swathes of grassland on both serpentine and non-serpentine soils in the Pennsylvania and Maryland Piedmont. In particular, high-intensity fires, as would occur during a drought, would burn much of the organic matter out of the soil, rendering it "barren" again. While the extensive use of fire ceased upon European settlement, the serpentine barrens reverted to forest much more slowly; these areas also made poor cropland, and were presumably grazed, if used at all. Mining of magnesite, chrome, and feldspar on the barrens may have encouraged logging, and in that sparsely settled area, little could be done to check fires, which often swept hundreds of acres. As late as 1919, spring fires were deliberately set at Goat Hill to clear land for grazing.

During the latter half of the twentieth century, improved fire-fighting equipment and denser settlement largely put an end to these wildfires, and the grasslands began to disappear, replaced by greenbrier thickets and forest. To check the loss of grasslands, landowners and volunteers have used a variety of techniques. Manual cutting of small trees and greenbrier, and judicious annual mowing of grasslands, can delay succession to thicket and woodland. Prescribed fire is also valuable for maintenance, but requires a large investment in equipment, personnel, and regulatory compliance, and high-intensity fires capable of reversing soil accumulation can be difficult to achieve. Several areas have been restored by scraping, bulldozing away existing soil to expose serpentine rock to weather afresh, generally with good results. While it may be unusual to think of human disturbance as ecologically beneficial, it is absolutely essential to maintain the serpentine barrens as we know them, and carries on an ancient tradition.

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