Serpentine Habitat

[Maybell Hughs]

Serpentinesoil 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.

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.

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 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.

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]

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]

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 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.

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]

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]

I have never been to the African grasslands, where lions, zebras, elephants, and wildebeests seem to be in continuous danger. I have, however, been to a Maryland habitat that few people know about, and that, even though lion-, zebra-, elephant- and wildebeest-less, reminded me strongly of those African savannas.

Serpentine soils form on a type of bedrock called serpentinite. This type of rock only exists in places where tectonic plates come into contact, fold, and volcanic activity occurs. This happened in our area about 480 million years ago when the Appalachian Mountains formed. Because of this, there is now an arc of serpentinite present in the Maryland-Pennsylvania area, parallel to the mountains.

Indeed, the Serpentine Grasslands of Maryland and Pennsylvania are some of the unique places where it is possible to find, for example, the rare moss pink, serpentine aster, or the sandplain gerardia (Fig. 3). It is also home to several endangered and rare species of butterflies and moths such as the Dusted or the Cobweb Skipper (Fig. 4).

Even though the plants and butterflies present in this habitat are relatively well-studied, we still know very little about what other organisms live in the grasslands. To remediate this, in my lab at the University of Maryland in College Park, we are working on trying to understand better what species of insects are present in the area.

For the moment, we are focusing on insect pollinators, and our first works indicate that the plants growing in these grasslands are pollinated not only by bees but also by hoverflies, showing how important these lesser-known pollinators may be to sustaining a very rare habitat of our region. (Take a look here to learn more about hoverflies as pollinators.)

The Serpentine Grasslands had not always been rare and endangered. Indeed, serpentine soils extended for quite an area in the Maryland-Pennsylvania region. So, what happened to this habitat that made it so rare today? Ecologists and historians can help us with this.

Like many habitats dominated by grasses, Serpentine Grasslands need fire to sustain themselves. In the absence of fire, pines and red cedars from the surrounding areas start establishing in the grasslands and compete with the grasses and all the rare plants, making the once grassland become an encroached pine forest. When the Europeans first arrived in our region, documents said that there were Serpentine Grasslands that extended for at least 130,000 acres. Today, Serpentine Grasslands occupy about 1.6% of that area.

Today, the Serpentine Barrens are protected and managed with fire in several parts of the state. A large part of these protected lands are not open to the public. However, we are lucky that some places are indeed accessible to the public and can be visited throughout the year.

The largest remnant of Serpentine Grasslands on the Eastern Coast of the US is west of Baltimore, in the Soldiers Delight Natural Environment Area. Another public land where some remains of Serpentine Grasslands are still visible is in Northern Baltimore, at Lake Roland.

3a8082e126