Natural Communities of Virginia - Terrestrial System - Low-Elevation Rock Outcrops and Barrens: Lichen / Bryophyte Boulderfields

The Natural Communities of Virginia
Classification of Ecological Community Groups
SECOND APPROXIMATION (Version 2.2)

Lichen / Bryophyte Boulderfields
Vegetation almost entirely dominated by lichens and bryophytes occupies exposed, minimally weathered boulderfields on mountain ridges of western Virginia. Boulderfield habitats have resulted from periglacial phenomena and the collapse of resistant strata from weathering and erosion of weaker underlying rocks. The most numerous and extensive exposed boulderfields are composed of sandstone or quartzite, with a few occurrences on metabasalt (greenstone) at higher elevations of the northern Blue Ridge. These habitats, where few vascular plants survive, are often densely populated by overlooked or cryptic species of lichens and moss. Dominant on boulders are umbilicate "rock tripe" lichens, including Umbilicaria mammulata, Umbilicaria muehlenbergii, and Lasallia papulosa. Also common are small, round, tightly attached patches of the golden moonglow lichen (Dimelaena oreina). Sheltered surfaces where detritus collects are often colonized by mosses. The most common of these are broom-mosses (Dicranum spp.), but Hedwig's rockmoss (Hedwigia ciliata) and other species are also present. The Appalachian rock polypody fern (Polypodium appalachianum) occurs frequently on weathered edges. Compositional differences between lichen/bryophyte communities of low- and middle-elevation acidic sedimentary boulderfields and high-elevation metabasalt boulderfields are evident, but difficult to characterize owing to a lack of specialized inventory.

Progressive, long-term weathering of exposed boulderfields results in slow invasion by trees such as yellow birch (Betula alleghaniensis) and American mountain-ash (Sorbus americana) at higher elevations, and sweet birch (Betula lenta) at lower elevations. Open boulderfields are favored by timber rattlesnakes (Crotalus horridus horridus), which often locate their hibernacula in the rocky substrates. These small-patch community types are uncommon and are primarily threatened by air pollution and acid precipitation.

Reference: Fleming and Coulling (2001).

Click on the images below to open a larger image in a separate window.

	Large-block quartzite boulderfield with sparse lichen cover, at Blackrock, Rockingham County (Shenandoah National Park). Photo © Gary P. Fleming.
	The umbilicate “rock tripe” Lasallia papulosa is the most conspicuous lichen on quartzite blocks at Blackrock, Rockingham County (Shenandoah National Park). Photo © Gary P. Fleming.
	Northern lowbush blueberry (Vaccinium angustifolium) invades the edge of a red sandstone talus field near the summit of Jack Mountain, Highland County (Highland Wildlife Management Area). Photo: Gary P. Fleming / © DCR Natural Heritage.
	Deeply piled metabasalt (greenstone) debris with diverse crustose lichens on a high-elevation, northern Blue Ridge boulderfield. Hawksill, Shenandoah National Park. Photo: Gary P. Fleming / © DCR Natural Heritage.

REPRESENTATIVE COMMUNITY TYPES:
To date, no quantitative data have been collected from lichen/bryophyte communities and no associations have been defined.

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The Natural Communities of Virginia Classification of Ecological Community Groups SECOND APPROXIMATION (Version 2.2)

The Natural Communities of Virginia
Classification of Ecological Community Groups
SECOND APPROXIMATION (Version 2.2)