Serpentine soil

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Solidago multiradiata, Erigeron aureus, and Adiantum aleuticum in rocky serpentine soil Serpentine habitat - Twin Sisters - Flickr - brewbooks.jpg
Solidago multiradiata , Erigeron aureus , and Adiantum aleuticum in rocky serpentine soil

Serpentine soil is an uncommon soil type produced by weathered ultramafic rock such as peridotite and its metamorphic derivatives such as serpentinite. More precisely, serpentine soil contains minerals of the serpentine subgroup, especially antigorite, lizardite, and chrysotile or white asbestos, all of which are commonly found in ultramafic rocks. The term "serpentine" is commonly used to refer to both the soil type and the mineral group which forms its parent materials.

Contents

Serpentine soils exhibit distinct chemical and physical properties and are generally regarded as poor soils for agriculture. The soil is often reddish, brown, or gray in color due to its high iron and low organic content. Geologically, areas with serpentine bedrock are characteristically steep, rocky, and vulnerable to erosion, which causes many serpentine soils to be rather shallow. [1] The shallow soils and sparse vegetation lead to elevated soil temperatures [2] and dry conditions. [1] Due to their ultramafic origin, serpentine soils also have a low calcium-to-magnesium ratio and have low levels of many essential nutrients such as nitrogen (N), phosphorus (P), and potassium (K). Serpentine soils contain high concentrations of heavy metals, including chromium, iron, cobalt, and nickel. [3] Together, these factors create serious ecological challenges for plants living in serpentine soils.

Parent rock

Serpentinite is a meta-igneous rock formed by the metamorphic reaction of olivine-rich rock, peridotite, with water. Serpentinite has a mottled, greenish-gray, or bluish-gray color and is often waxy to the touch. The rock often contains white streaks of chrysotile running through it, which are a type of naturally occurring asbestos. Asbestos is linked to an array of human health conditions such as mesothelioma from long-time exposure of breathing in the dust particles. Caution should be taken when working in serpentine soils or when working with crushed serpentine rocks.

Serpentinite most often forms in oceanic crust near the surface of the earth, particularly where water circulates in cooling rock near mid-ocean ridges: masses of the resulting ultramafic rock are found in ophiolites incorporated in continental crust near present and past tectonic plate boundaries.

Serpentine soils are derived from ultramafic rocks. Ultramafic rocks are igneous or metamorphic rocks that contain more than 70% iron or magnesium minerals. [4]

Distribution

Serpentine outcrop high in the Siskiyou Wilderness of northwest California--here Jeffrey pine dominates the landscape. Jeffrey pine Siskiyou Wilderness.jpg
Serpentine outcrop high in the Siskiyou Wilderness of northwest California—here Jeffrey pine dominates the landscape.

Serpentine soils are widely distributed on Earth, in part mirroring the distribution of ophiolites. There are outcroppings of serpentine soils in the Balkan Peninsula, Turkey, Newfoundland, the island of Cyprus, the Alps, Cuba, and New Caledonia. [2] In North America, serpentine soils also are present in small but widely distributed areas on the eastern slope of the Appalachian Mountains in the eastern United States. [5] However, California has the majority of the continent's serpentine soils.

Botany

Soldiers Delight Natural Environment Area in Maryland Soldiers-Delight-Walking-Path.jpg
Soldiers Delight Natural Environment Area in Maryland

Ecologically, serpentine soils have three main traits: poor plant productivity, high rates of endemism, and vegetation types that are distinct from neighboring areas. [6]

Serpentine plant communities range from moist bogs and fens to rocky barrens and must be able to tolerate the harsh environmental conditions of such poor soil. As a result, they are often drastically different from non-serpentine soil areas bordering the serpentine soils. [4] Vegetative characteristics are often shared among the types of flora found on serpentine soils. They will exhibit a "stunted" growth habit, with dull waxy, gray-green leaves (seen in Eriogonum libertini ), which allow for water retention and sunlight reflection respectively. [7] Other possible phenotypic traits include pigmented stems (as seen in the Streptanthus howellii ) and occasionally a carnivorous nature as seen in the Darlingtonia californica . Some examples of common serpentine tolerant plants include gray pine ( Pinus sabiniana ), Jeffrey Pine ( Pinus jeffreyi ), California lilac (Ceanothus sp.), manzanita (Arctostaphylos sp.), live oak (Quercus sp.), California redbud ( Cercis occidentalis ), California buckeye ( Aesculus californica ), California laurel (bay tree) ( Umbellularia californica ), and the ferns Aspidotis densa and Polystichum lemmonii .

Areas of serpentine soil are also home to diverse plants, many of which are rare or endangered species such as Acanthomintha duttonii , Pentachaeta bellidiflora , and Phlox hirsuta . In California, 45% of the taxa associated with serpentine are rare or endangered. [8] In California, shrubs such as leather oak ( Quercus durata ) and coast whiteleaf manzanita ( Arctostaphylos viscida ssp. pulchella) are typical of serpentine soils. [4]

In order to overcome the chemical and physical challenges presented by serpentine soils, plants have developed tolerances to drought, heavy metals, and limited nutrients. [4] Low calcium:magnesium ratios cause limited root growth and root activity, weak cell membranes, and reduced uptake of essential nutrients. [9] An adaptive mechanism to high magnesium soils allocates more resources to deep-growing roots. [7] Heavy metals stunt growth, induce iron deficiency, cause chlorosis, and restrict root development. [9] [7] Multiple adaptive mechanisms to heavy metals include the exclusion of metals by restricting the uptake by the roots, compartmentalization of metals in various organs, or the development of toxicity tolerance. [7] In nitrogen-poor sites, physiological effects on plants include impaired protein synthesis, chlorosis, reduced leaf turgor, reduced leaf and tiller number, reduced growth rate, and low seed yield. [9] Low phosphorus levels cause similar effects of low nitrogen but also cause reduced seed size, lower root to shoot ratios, and increased water stress. [9] Low soil moisture causes reduced nutrient uptake and transport, decreased stomatal opening, and reduced photosynthetic capacity, and also reduces plant growth and productivity. [9] Serpentine plants have strongly developed root systems to facilitate uptake of water and nutrients. [7] For example, Noccaea fendleri (aka Fendler's penny grass) is a hyper-accumulator of nickel and Sedum laxum expresses succulence. In some cases, symbioses with serpentine tolerant ectomycorrhizal help facilitate plants’ adaptation to edaphic stressors on serpentine. [7]

Adaptation to serpentine soils has evolved multiple times. [7] [4] [1] [10] Serpentine-tolerant plants are evolutionarily younger than non-serpentine plants. [11] The heterogeneity of serpentine communities coupled with their patchy distribution limits gene flow but promotes speciation and diversification. [11] Habitat heterogeneity is an important contributor to the level of endemism and biodiversity in this system. Although the patchy distribution is attributed to the high rates of speciation in serpentine communities, there are a number of challenges associated with this. The spatial isolation from source and other populations limit gene flow, [4] which could make these populations vulnerable to changing environmental conditions. In addition, there is high gene flow with the non-serpentine communities that can cause genotypic pollution, hybridization, and nonviable offspring. [4]

Bioremediation

The unique plants that survive in serpentine soils have been used in the process of phytoremediation, a type of bioremediation. Since these plants developed specialized adaptations to high concentrations of heavy metals, they have been used to remove heavy metals from polluted soil. [12]

Serpentine barrens

Unlike most ecosystems, in serpentine barrens, there is less plant growth closer to a stream, due to toxic minerals in the water. Stream-serpentine-barrens-lancaster-pa.jpg
Unlike most ecosystems, in serpentine barrens, there is less plant growth closer to a stream, due to toxic minerals in the water.

Serpentine barrens are a unique ecoregion found in parts of the United States in small but widely distributed areas of the Appalachian Mountains and the Coast Ranges of California, Oregon, and Washington. [13] Species-rich archipelagos of communities comprise 1.5% of the state's land area.[ specify ] In California, 10% of the state's plants are serpentine endemics. The barrens occur on outcrops of altered ultramafic ophiolites.

They are named for minerals of the serpentine group, resulting in serpentine soils, with unusually high concentrations of iron, chromium, nickel, and cobalt. Serpentine barrens, as at Grass Valley, California, often consist of grassland or savannas in areas where the climate would normally lead to the growth of forests. [14]

Serpentine soils can be amended to support crops and pasture land for cattle grazing. This can be done by adding ample amounts of gypsum to the soil. By adding gypsum a more favourable calcium-to-magnesium ratio can be developed, creating a better balance of plant nutrients. This, however, poses a possible implication to grazing cattle. An article from the Journal of Trace Elements in Medicine and Biology discerned that 20% of the grazing animals had toxic levels of nickel in their kidneys, and 32% had toxic levels of copper in their liver. [15] Further study is needed to see if this will potentially have a negative effect on human health as it pertains to beef consumption.

Examples

Soldiers Delight Natural Environment Area in Baltimore County, Maryland, covers 1,900 acres of serpentine barren. The area has over 38 rare, threatened, and endangered plant species; as well as rare insects, rocks, and minerals. [16]

Serpentine Barrens in Rock Springs Nature Preserve, Lancaster County, Pennsylvania Rocksprings-serpentinebarrens-lancaster-pa.jpg
Serpentine Barrens in Rock Springs Nature Preserve, Lancaster County, Pennsylvania

Rock Springs Nature Preserve in Lancaster County, Pennsylvania is a 176-acre (71 ha) property conserved by the Lancaster County Conservancy that is a prime example of a serpentine barren. It was originally a grassland, but wildfire suppression led to the conversion of the area to forest. This barren contains the rare serpentine aster ( Symphyotrichum depauperatum ), as well as a number of rare species of moths and skippers. [17]

In Chester County, Pennsylvania, the Nottingham Park, aka Serpentine Barrens, was recommended by UMCES as deserving of National Natural Landmark designation, on numerous grounds. They included supporting a number of rare and endemic species, an intact population of pitch pine, and also the site having historic significance. [14] Since 1979, the Nature Conservancy has worked with the local community to protect and preserve several tracts in the State-Line Serpentine Barrens which are home to this fragile habitat. [18]

Buck Creek Serpentine Barrens in Nantahala National Forest in Clay County, North Carolina, is another example. Dominant rock types are serpentinized dunite and olivine, with variable soil depths ranging from 0 to 60 centimetres (0 to 24 inches) and rock outcrops representing 5–10% of the local landscape. The U.S. National Vegetation Classification for this community is "Southern Blue Ridge Ultramafic Outcrop Barren" and believed to be unique to the Buck Creek area. In 1995, the United States Forest Service began active conservation management of the site, primarily with prescribed controlled burns, which, along with some manual cover removal, has been successful in regenerating populations of previously sparse species. In addition to over 20 conservationally listed plant species, Rhiannon’s aster ( Symphyotrichum rhiannon ) was described in 2004 and is endemic to these barrens. [19]

See also

Related Research Articles

<span class="mw-page-title-main">Serpentine subgroup</span> Group of phyllosilicate minerals

Serpentine subgroup are greenish, brownish, or spotted minerals commonly found in serpentinite. They are used as a source of magnesium and asbestos, and as decorative stone. The name comes from the greenish color and smooth or scaly appearance from the Latin serpentinus, meaning "serpent rock".

<span class="mw-page-title-main">Chromite</span> Crystalline mineral

Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr2O4). A substitution of the element aluminium can also occur, leading to hercynite (FeAl2O4). Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy.

<span class="mw-page-title-main">Peridotite</span> Coarse-grained ultramafic igneous rock type

Peridotite ( PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from Earth's mantle, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole.

<span class="mw-page-title-main">Ultramafic rock</span> Type of igneous and meta-igneous rock

Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals. The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.

<span class="mw-page-title-main">Serpentinite</span> Rock formed by hydration and metamorphic transformation of olivine

Serpentinite is a metamorphic rock composed predominantly of one or more serpentine group minerals formed by near to complete serpentinization of mafic to ultramafic rocks. Its name originated from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called serpentine or serpentine rock, particularly in older geological texts and in wider cultural settings.

<span class="mw-page-title-main">Serpentinization</span> Formation of serpentinite by hydration and metamorphic transformation of olivine

Serpentinization is a hydration and metamorphic transformation of ferromagnesian minerals, such as olivine and pyroxene, in mafic and ultramafic rock to produce serpentinite. Minerals formed by serpentinization include the serpentine group minerals, brucite, talc, Ni-Fe alloys, and magnetite. The mineral alteration is particularly important at the sea floor at tectonic plate boundaries.

<span class="mw-page-title-main">Anthophyllite</span> Silicate amphibole mineral

Anthophyllite is an orthorhombic amphibole mineral: ☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure), magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthophyllite are lamellar or fibrous and are classed as asbestos. The name is derived from the Latin word anthophyllum, meaning clove, an allusion to the most common color of the mineral. The Anthophyllite crystal is characterized by its perfect cleavage along directions 126 degrees and 54 degrees.

Talc carbonates are a suite of rock and mineral compositions found in metamorphosed ultramafic rocks.

<i>Streptanthus glandulosus <span style="font-style:normal;">subsp.</span> niger</i> Species of herb

Streptanthus glandulosus subsp. niger is an endangered subspecies of flowering plant within the family Brassicaceae. Like other genus members, this herb has wavy petal margins with perimeter calluses that discourage larval herbivory. This plant is endemic to the Tiburon Peninsula of Northern California, and occurs at elevations below 150 m on serpentine grasslands. The common name for this subspecies is Tiburon jewelflower or black jewelflower. This annual herb blooms in May and June and displays dark purple sepals. The etymology of this genus scientific name derives from the Greek word streptanthus, meaning twisted flower, with reference to the notable wavy margins of the petals. The subspecies name niger relates to the color of the seeds being black, although an alternate account cites the dark color of the petals as the source of the appellation.

Lateritic nickel ore deposits are surficial, weathered rinds formed on ultramafic rocks. They account for 73% of the continental world nickel resources and will be in the future the dominant source for the mining of nickel.

<span class="mw-page-title-main">San Benito Mountain</span>

San Benito Mountain is the highest mountain in the Diablo Range of California. The summit is at an elevation of 5,267 feet (1,605 m). The rock is composed of asbestos (chrysotile), an ultramafic rock. It weathers to produce serpentine soils with characteristically low levels of nutrients like nitrogen, phosphorus, potassium, and calcium, and high levels of magnesium and heavy metals including nickel and chromium. This means little vegetation grows in the area though there are some plants that only grow on such soils like the local endemic San Benito evening primrose. The Clear Creek Management Area includes the San Benito Mountain Research Natural Area, recognized for its unique pine and incense cedar forest assemblage. The Mediterranean climate is punctuated by cool, wet winters and hot, dry summers.

<span class="mw-page-title-main">Barren vegetation</span> Area of land where plant growth may be limited

Barren vegetation describes an area of land where plant growth may be sparse, stunted, and/or contain limited biodiversity. Environmental conditions such as toxic or infertile soil, high winds, coastal salt-spray, and climatic conditions are often key factors in poor plant growth and development. Barren vegetation can be categorized depending on the climate, geology, and geographic location of a specific area.

<i>Aspidotis densa</i> Species of fern

Aspidotis densa is a species of fern in the Cheilanthoid subfamily, known by the common name Indian's dream or Serpentine fern or dense lace fern. It is native to the west coast of North America from British Columbia to California and east to the Rocky Mountains in Idaho, Montana, and Wyoming; there is a disjunct population on serpentine soils in Quebec.

<i>Camissonia benitensis</i> Species of flowering plant

Camissonia benitensis is a species of evening primrose known by the common names San Benito suncup and San Benito evening primrose. It is endemic to the Diablo Range of the South Coast Ranges of California, where its range includes far southern San Benito County, far western Fresno County, and far eastern Monterey County.

<i>Harmonia stebbinsii</i> Species of flowering plant

Harmonia stebbinsii is a species of flowering plant in the family Asteraceae known by the common name Stebbins' tarweed, or Stebbins' madia. It is endemic to northern California, where it is limited to the Klamath Mountains and adjacent slopes of the North Coast Ranges. It is a member of the serpentine soils plant community in these mountains, found at elevations of 1100–1600 meters. It is a rare annual herb producing a bristly stem up to about 25 centimeters tall studded with black resin glands. Its bristly leaves grow up to about 2 centimeters long and are mostly gathered near the base of the plant. The inflorescence is an array of flower heads lined with hairy, glandular, purple-tipped phyllaries. The head has a few yellow ray florets several millimeters long and yellow disc florets. The fruit is an achene tipped with a pappus.

<i>Adiantum viridimontanum</i> Species of fern

Adiantum viridimontanum, commonly known as Green Mountain maidenhair fern, is a fern found only in outcrops of serpentine rock in New England and Eastern Canada. The leaf blade is cut into finger-like segments, themselves once-divided, which are borne on the outer side of a curved, dark, glossy rachis. These finger-like segments are not individual leaves, but parts of a single compound leaf. The "fingers" may be drooping or erect, depending on whether the individual fern grows in shade or sunlight. Spores are borne under false indusia at the edge of the subdivisions of the leaf, a characteristic unique to the genus Adiantum.

Dubakella soil series is the name given to a reddish-brown stony loam soil which has developed on ultramafic rock containing magnesium minerals such as serpentine or asbestos. This soil occurs from southwestern Oregon south to the Coast Ranges of California near Healdsburg, and it also is found in the Sierra Nevada mountains and foothills.

Mycorrhizal amelioration of heavy metals or pollutants is a process by which mycorrhizal fungi in a mutualistic relationship with plants can sequester toxic compounds from the environment, as a form of bioremediation.

The Staten Island Serpentinite locality is a southward extension of the New England Uplands, adjacent to the Manhattan Prong. It includes Todt Hill on Staten Island, which is the highest point along the Atlantic Seaboard south of Maine, at 410 feet (120 m) above sea level. "Todt" is a Dutch word meaning "dead." This hill perhaps received its name from the Dutch settlers because the hilltops overlooking The Narrows consisted of scattered treeless rocky exposures. The chemical character of the bedrock was, in part, the reason for this. Much of Staten Island is covered by the Harbor Hill moraine, the terminal moraine of the last Wisconsin Stage glacier. However, ledges of bedrock consisting of serpentinite are exposed throughout the upland areas on Staten Island. Grymes Hill, the second highest point on Staten Island and just a few miles from Todt Hill has similar bedrock characteristics. Serpentine, the dominant mineral in serpentinite, is rich in magnesium, an element that most plants cannot tolerate in high concentrations. The enrichment of magnesium in the thin serpentine soil covering the glacier-scoured hilltops is probably responsible for the original barren exposures on Todt Hill.

References

  1. 1 2 3 Brady, Kristy U.; Kruckeberg, Arthur R.; Bradshaw Jr., H.D. (2005). "Evolutionary Ecology of Plant Adaptation to Serpentine Soils". Annual Review of Ecology, Evolution, and Systematics. 36: 243–266. doi:10.1146/annurev.ecolsys.35.021103.105730.
  2. 1 2 Kruckeberg, Arthur R (2002). Geology and plant life : the effects of landforms and rock types on plants. University of Washington Press. ISBN   978-0-295-98203-8. OCLC   475373672.[ page needed ]
  3. ↑ Chiarucci, Alessandro; Baker, Alan J. M. (2007). "Advances in the ecology of serpentine soils". Plant and Soil. 293 (1–2): 1–2. Bibcode:2007PlSoi.293....1C. doi: 10.1007/s11104-007-9268-7 . S2CID   35737876.
  4. 1 2 3 4 5 6 7 Kruckeberg, Arthur R (2006). Introduction to California soils and plants : serpentine, vernal pools, and other geobotanical wonders. University of California Press. ISBN   978-0-520-23372-0. OCLC   928683002.[ page needed ]
  5. ↑ Dann, Kevin T. (1988). Traces on the Appalachians: A Natural History of Serpentine in Eastern North America . New Brunswick: Rutgers University Press. ISBN   0-8135-1323-5.[ page needed ]
  6. ↑ Whittaker, R.H. (1954). "The ecology of serpentine soils". Ecology. 35 (2): 258–288. Bibcode:1954Ecol...35..258W. doi:10.2307/1931126. JSTOR   1931126.
  7. 1 2 3 4 5 6 7 Harrison, Susan; Rajakaruna, Nishanta (2011). Serpentine : the evolution and ecology of a model system. University of California Press. ISBN   9780520268357. OCLC   632224033.[ page needed ]
  8. ↑ Safford, H. D.; Viers, J. H.; Harrison, S. P. (2005). "Serpentine Endemism in the California Flora: A Database of Serpentine Affinity". Madroño. 52 (4): 222. doi:10.3120/0024-9637(2005)52[222:SEITCF]2.0.CO;2.
  9. 1 2 3 4 5 Zefferman, Emily; Stevens, Jens T.; Charles, Grace K.; Dunbar-Irwin, Mila; Emam, Taraneh; Fick, Stephen; Morales, Laura V.; Wolf, Kristina M.; Young, Derek J. N.; Young, Truman P. (2015). "Plant communities in harsh sites are less invaded: A summary of observations and proposed explanations". AoB Plants. 7: plv056. doi:10.1093/aobpla/plv056. PMC   4497477 . PMID   26002746.
  10. ↑ Arnold, Brian J.; Lahner, Brett; Dacosta, Jeffrey M.; Weisman, Caroline M.; Hollister, Jesse D.; Salt, David E.; Bomblies, Kirsten; Yant, Levi (2016). "Borrowed alleles and convergence in serpentine adaptation" (PDF). Proceedings of the National Academy of Sciences. 113 (29): 8320–5. Bibcode:2016PNAS..113.8320A. doi: 10.1073/pnas.1600405113 . PMC   4961121 . PMID   27357660.
  11. 1 2 Anacker, Brian L.; Whittall, Justen B.; Goldberg, Emma E.; Harrison, Susan P. (2011). "Origins and Consequences of Serpentine Endemism in the California Flora". Evolution. 65 (2): 365–76. doi: 10.1111/j.1558-5646.2010.01114.x . PMID   20812977. S2CID   22429441.
  12. ↑ NATO Advanced Study Institute on Phytoremediation of Metal-Contaminated Soils, Morel, J.-L., Echevarria, G., & Goncharova, N. (2006). Phytoremediation of metal-contaminated soils. NATO science series, v. 68. Dordrecht: Springer.
  13. ↑ Anderson, Roger C., et al., Savannas, Barrens, and Rock Outcrop Plant Communities of North America, Ch. 19, Cambridge University Press, 1999, ISBN   0-521-57322-X
  14. 1 2 "Evaluation of the Nottingham Park Serpentine Barrens", UMCES-AL, Retrieved May 10, 2009.
  15. ↑ Miranda, M.; Benedito, J.L.; Blanco-Penedo, I.; López-Lamas, C.; Merino, A.; López-Alonso, M. (2009). "Metal accumulation in cattle raised in a serpentine-soil area: Relationship between metal concentrations in soil, forage and animal tissues". Journal of Trace Elements in Medicine and Biology . 23 (3): 231–8. doi:10.1016/j.jtemb.2009.03.004. PMID   19486833.
  16. ↑ "Maryland Department of Natural Resources - Maryland Park Service". Archived from the original on 2012-11-08. Retrieved 2012-11-07.[ full citation needed ]
  17. ↑ "Rock Springs Nature Preserve", Lancaster County Conservancy Website, Retrieved May 10, 2009. Archived February 22, 2009, at the Wayback Machine
  18. ↑ "Places We Protect: State-Line Serpentine Barrens, Pennsylvania", Retrieved July 20, 2020.
  19. ↑ USFS (n.d.). "Restoration of Buck Creek Serpentine Barrens, Tusquitee Ranger District, Nantahala National Forest". www.fs.fed.us. United States Forest Service, USDA. Archived from the original on 4 September 2021. Retrieved 4 September 2021.
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