About Mafic Barrens

 Considered to be the crown jewel of Virginia’s Piedmont ecosystems, the Piedmont Mafic Barren is a rare commodity facing enormous pressures.  The Mafic Barren community requires expansive, generally flat, surface bedrock that is not completely shaded out by surrounding forests. Not only is it a globally rare plant community, but it being been pushed out or compromised in most of its range. Being a naturally uncommon habitat type, it exists at an elevated level of vulnerability. They are scattered throughout the Virginia Piedmont as small patches in larger forests and sometimes one may even find a remnant lurking in an old field. One of the primary risks at present is the unfortunate human behavior known as “fire prevention”. Fire prevention is one of our most ecologically disruptive behaviors. Most of our plant communities evolved with the presence of regular fires. In fact, our plant community variety is, in large part, due to a long history of landscape disturbance resulting from fire. The Piedmont Mafic Barren, along with the savannas, woodlands, prairies, and even wetlands, is in sharp decline due to this factor. The Mafic Barren derives the name “mafic” from the bedrock it occurs on. While there is some variety in that bedrock in our region, it always contains some blend of mafic minerals (dark, cation-rich). Examples include metabasalt, amphibolite, and most commonly, base-rich gneiss (Ragged Mountains). Rarely is the plant community observed on sedimentary rocks, and when that is the case they are felsic in nature (high in potassium and calcium feldspars). This bedrock creates a situation where nutrients are available to plants for uptake. The relatively gentle slope of these sites results in extensive soil pockets and organic root mats. Despite having high levels of cations and being known therefor as “base-rich”, the pH is generally acidic to neutral. Conditions at the Piedmont Mafic Barren sites are harsh, and the plants are well-adapted to those conditions. There is very little water present (with the exception of occasional ground water seepages), and when it rains the water runs off swiftly. The expansive bedrock exposure limits tree growth so the sites are exposed to full sun and adverse weather conditions.

Thanks to Devin Floyd of Center for Urban Habitats for assistance with words.