Serpentine Barrens

Goat Hill Serpentine Barrens in SE Pennsylvania. Photo by Josh Klostermann

Serpentine Barrens are unique ecoregions that can be found globally, in small patchy pockets of land with serpentine bedrock and soil. The term "serpentine barren" generally refers to a serpentine outcrop and its associated vegetation. These habitats are notable for their distinct flora with high rates of endemism. The difference in vegetative communities is the product of chemical, physical, and biotic edaphic factors but is primarily driven by the toxic chemical composition of the serpentine bedrock and soil. These systems are used to study edaphic endemism and plant speciation. [2] They are also used as an analog to brownfields in restoration ecology because of the high heavy metal content in the soil.

Rock formation:

Serpentine talus. Photo by Josh Klostermann

Serpentine is not the name of a single mineral. Instead, it is a name used for a large group of minerals that fit this generalized formula: (X)2-3(Y)2O5(OH)4.

In this formula, X will be one of the following metals: magnesium, iron, nickel, aluminum, zinc, or manganese; and, Y will be silicon, aluminum, or iron. The appropriate generalized formula is therefore as follows: (Mg,Fe,Ni, Mn,Zn)2-3(Si,Al,Fe)2O5(OH)4.

Chrysotile, antigorite, and lizardite are three of the primary serpentine minerals. There are many other serpentine minerals, most of which are rare.

Serpentine minerals form where peridotite, dunite, and other ultramafic rocks undergo hydrothermal metamorphism. Ultramafic rocks are rare at Earth's surface but are abundant at the oceanic moho, the boundary between the base of the oceanic crust and the upper mantle.

They are metamorphosed at convergent plate boundaries where an oceanic plate is pushed down into the mantle. This is where they are subjected to hydrothermal metamorphism. The source of water for this process is seawater entrained in the rocks and sediments of the oceanic slab.

During hydrothermal metamorphism, olivine and pyroxene minerals are transformed into or are replaced by serpentine minerals. Some of the metamorphic rocks produced here are composed almost entirely of serpentine minerals. These serpentine-rich rocks are known as "serpentinites."

Extensive areas of Earth's surface are underlain by serpentinites. These areas occur near present or ancient convergent plate boundaries. They are locations where remnants of an oceanic plate are exposed at the surface. The remnant portion of the plate was either thrust up onto land, accreted onto the edge of a landmass, or exposed by uplift and deep weathering.

These areas of exposed oceanic plate are known as ophiolites. They are often the source of valuable minerals that might include magnetite, chromite, chrysoprase, jade, and serpentine.

Article by: Hobart M. King, PhD, RPG [6]

Edaphic endemism:

"Although speciation has been a central focus in evolutionary biology for more than a century, there are very few case studies where we have a good understanding of the exact forces that may have acted in the diversification of a group of organisms. In order to examine such forces, botanists have often focused on closely related plants that are found under contrasting soil conditions. The study of such edaphically differentiated plants has provided valuable insight to the role of natural selection in evolution. " - Nishanta Rajakaruna, The Edaphic Factor in the Origin of Plant Species [5]

Edaphic endemics are plants or animals that are endemic (or restricted) to a certain type of soil. Some examples of edaphic endemics include; sand wasps (Bembix sp.) on sandy soils, the serpentine aster (Symphyotrichum depauperatum) on ultramafic soils, and many others on various different soil substrates.

Together the chemical, physical, and biological factors that characterize serpentine soils culminate in the term coined by (our lord and savior) Hans Jenny in 1980, known as the "Serpentine Syndrome". This term is an expression used to indicate the cumulative effect that these 3 factors have on the development of vegetative communities growing in serpentine soil. [2] The "Serpentine syndrome" is a classic and well-studied case of edaphic plant endemism.

Serpentine soils are characterized by their harsh chemical composition. They contain metals such as iron, nickel, chromium, and cobalt which are toxic to most plants. They are also deficient in essential plant nutrients such as N, P, K, have low Mg:Ca ratios, and steep ph gradients. [1] Their physical conditions also make it tough for plants to adapt. Outcrops are often found on steep rocky slopes, with high rates of erosion and therefore shallow topsoils. These physical conditions create an environment that holds little moisture and low nutrient levels. The biota found using these soils is generally sparse and the little plant life leads to further erosion, which also increases soil temperatures. [2]

From a birds-eye view, serpentine areas look like islands with steep vegetative gradients as boundaries. They are like archipelagoes of specialized habitat for species with disjunct or endemic distributions. This makes them a textbook example for the study of plant speciation and island biogeography. Vegetative communities growing in serpentine barrens differ from surrounding areas by having a notably distinct physiognomy and community structure, low species richness, a dominance of specific taxa, a predominance of xerophytic species, low productivity, and the co-existence of high and low ph-tolerant species. [1]

Pennsylvannia and Maryland Serpentine Barrens:

Taken from Brooks, R. R. 1987. Serpentine and its Vegetation: a Multi-disciplinary Approach. Dioscorides Press, Portland

The serpentine barrens of Eastern North America are found in thin, patchy, sinusoidal-bands, that work their way down the coast. Historically, the barrens of Pennsylvania and Maryland were maintained as grasslands for hunting grounds by the Susquehannock and other unknown Native American Tribes. Fires deliberately set by Native Americans were responsible for maintaining the grassland/savannah communities found in the serpentine barrens of the piedmont plateau. Post european invasion and settlement, these areas were used for grazing due to their "barrenness". Barrens that were not grazed by livestock transitioned into a forest habitat. By 1930 almost all grazing in this area had ceased and conifer invasion and expansion began. Presently, afforestation has occurred in more than 90% of undeveloped serpentine barrens due to fire suppression. [1]

Flora:

Below are compiled lists of the flora found at Soldiers Delight Serpentine Barrens. These species are typical of the Eastern Serpentine Region of SE Pennsylvania and Maryland.

List of Wildflowers of Soldiers Delight [1]

List of Woody Plants of Soldiers Delight [2]

List of Ferns of Soldiers Delight [3]

List of Lichens of Soldiers Delight [4]

Threats and Conservation:

Major threats to the eastern serpentine barrens are afforestation, invasive species, and development. Current restoration efforts such as prescribed burns and tree removals are being used to improve the health and quality of these globally important habitats. [7]

Gallery:

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Citations:

[1] Anderson, R. C., J. S. Fralish, and J. M. Baskin, editors. 1999. Savannas, barrens, and rock outcrop plant communities of North America. Cambridge University Press, Cambridge, UK ; New York, NY, USA.

[2] Brady, K. U., A. R. Kruckeberg, and H. D. Bradshaw Jr. 2005. Evolutionary Ecology of Plant Adaptation to Serpentine Soils. Annual Review of Ecology, Evolution, and Systematics 36:243–266.

[3] Jenny, H. 1980. The Soil Resource. Springer New York, New York, NY.

[4] Nottingham_Evaluation_Review.pdf. (n.d.). .

[[[5]]] Rajakaruna, N. 2004. The Edaphic Factor in the Origin of Plant Species. International Geology Review 46:471–478.

[6]Serpentine: mineral, gem, ornamental stone, asbestos source. (n.d.). . https://geology.com/minerals/serpentine.shtml.

[7] Latham, R. E. 1993. The Serpentine Barrens of Temperate Eastern North America: Critical Issues in the Management of Rare Species and Communities. Bartonia:61–74.