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Central Appalachian Mafic Barren in the Blue Ridge [HQ]

Posted: Fri May 20, 2011 5:28 pm
by edfrank
Central Appalachian Mafic Barren in the Blue Ridge [HQ]
mafic.JPG (37.52 KiB) Viewed 1607 times
Virginia Natural Heritage Program ecologists Karen Patterson and Gary Fleming explore a newly documented occurrence of a Central Appalachian Mafic Barren, a community only known from the Northern Blue Ridge of Virginia.


Re: Central Appalachian Mafic Barren in the Blue Ridge [HQ]

Posted: Mon May 23, 2011 7:33 am
by Joe
I wonder how it might change if protected from fire and grazing? I doubt it could remain baren for long, regardless of the geology.

Re: Central Appalachian Mafic Barren in the Blue Ridge [HQ]

Posted: Mon May 23, 2011 8:47 am
by edfrank

The serpentine barrens form because of the poor soil derived and heavy metal toxicity from the bedrock. I was surprised but Wikipedia actually does a pretty good description of the soil characteristics:
A serpentine soil is derived from ultramafic rocks, in particular serpentinite, a rock formed by the hydration and metamorphic transformation of ultramafic rock from the Earth's mantle.

The soils derived from ultramafic bedrock give rise to unusual and sparse associations of edaphic (and often endemic) plants that are tolerant of extreme soil conditions, including:

- low calcium-to-magnesium ratio
- lack of essential nutrients such as nitrogen, potassium, and phosphorus
- high concentrations of the heavy metals (more common in ultramafic rocks).

These plants are commonly called serpentine endemics, if they grow only on these soils. (Serpentinite is composed of the mineral serpentine, but the two terms are often both used to mean the rock, not its mineral composition.)
The key points above are the complete lack of several key nutrients, and heavy metal toxicity. Plants that do grow there often are often specially adapted to grow in these unusual conditions and endemic to these uncommon settings. Therefore many of these species are rare or endangered species. "Normal" plants and trees that manage to colonize around the edges of these barrens tend to be stunted and grow poorly. The heavy metal toxicity can get even worse. There is a distinctive black band formed by exposures of a particular marine shale - I don't remember the name - in parts of South Dakota. It is seleniferous - meaning it contains high levels of selenium. It is barren and black because the levels are too toxic for plants to grow in the soils directly derived from the unit.

There are a number of serpentine barrens scattered across the eastern United States and around the world. Notable ones are found in eastern PA. There are other examples in Virginia, Maryland, and New York. I am not sure of the location of any in New England. They are not patches created by grazing or fires as are some other barren types, and will persist without either of these activities occurring.