High-Elevation Seepage Swamps
This group contains saturated, coniferous or mixed forests of gently sloping stream headwaters, large spring seeps, and ravine bottoms at elevations above 900 m (3,000 ft). These communities are locally scattered in the higher mountains of western Virginia on various geologic substrates and soils, almost all of which are strongly to extremely acidic. Habitats feature pronounced hummock-and-hollow microtopography, with braided streams, muck-filled depressions, and lush bryophyte cover. Eastern hemlock (Tsuga canadensis), yellow birch (Betula alleghaniensis), and red maple (Acer rubrum) are the most common trees. Locally, red spruce (Picea rubens) or eastern white pine (Pinus strobus) may be co-dominants. Shrub layer composition and density is variable; deciduous hollies (Ilex verticillata and Ilex montana), several blueberries (particularly Vaccinium corymbosum, Vaccinium simulatum, and Vaccinium angustifolium), great rhododendron (Rhododendron maximum), mountain laurel (Kalmia latifolia), speckled alder (Alnus incana ssp. rugosa), and witch hazel (Hamamelis virginiana var. virginiana) may be abundant. Characteristic herbs of these swamps include marsh marigold (Caltha palustris), star sedge (Carex echinata ssp. echinata), finely-nerved sedge (Carex leptonervia), eastern rough sedge (Carex scabrata), three-seeded sedge (Carex trisperma), slender wood reedgrass (Cinna latifolia), tall flat-topped white aster (Doellingeria umbellata, = Aster umbellatus), spinulose wood fern (Dryopteris carthusiana), slender mannagrass (Glyceria melicaria), whorled wood aster (Oclemena acuminata = Aster acuminatus), cinnamon fern (Osmundastrum cinnamomeum var. cinnamomeum), American false-hellebore (Veratrum viride), and smooth white violet (Viola mackloskeyi var. pallens). Communities in this group are naturally rare due to the scarcity of flat or gentle, wet habitats in the higher Appalachians. Beavers have partially destroyed fine examples of these swamps at several sites, and the integrity of many stands has been compromised by extensive hemlock mortalilty due to outbreaks of hemlock woolly adelgid (Adelges tsugae).
References: Fleming and Coulling (2001), Rawinski et al . (1994), Rawinski et al . (1996).
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High-elevation seepage swamp dominated by red spruce (Picea rubens) at the headwaters of Slabcamp Run on Allegheny Mountain, Highland County (George Washington and Jefferson National Forests). Gary P. Fleming / © DCR Natural Heritage.
Lush bryophyte cover and dense patches of slender mannagrass (Glyceria melicaria) in a Central Appalachian hemlock - yellow birch seepage swamp. The Limberlost, headwaters of White Oak Canyon, Madison County (Shenandoah National Park).Gary P. Fleming / © DCR Natural Heritage.