Boulderfields, too, are most unusual natural places. They consist of many acres of jumbled boulders, mostly moss-covered and with a rich assemblage of wildflowers in late spring and early summer under such mid-altitude trees as yellowwood (Cladrastris kentukea), American basswood, and yellow birch. Currants and gooseberries are common shrubs found in these areas. Usually boulderfields occur above 3,200 feet elevation, and they almost always are found in steep, north-facing coves. Although it is not known exactly how they formed, boulders undoubtedly were created from bedrock during the last ice age, approximately 10,000 to 20,000 years ago. Even though the northern glaciers never reached the southern Appalachians, it is believed that the freezing and thawing and resulting fracturing and uplifting of bedrock during the ice age were primarily responsible for producing the boulderfields.
The most mysterious habitats in the southern Appalachians, though, are those known as balds. Balds are defined as high-altitude open areas devoid of trees, occurring as either shrub-dominated areas or tundralike grasslands at or near the summits of our highest mountains at the edges of Canadian-zone spruce-fir forests. Shrub balds, which usually consist of nearly impenetrable rhododendrons (Rhododrendron maximum or R. carolinianum at lower elevations and R. catawbiense at higher elevations) and mountain laurel (Kalmia latifolia), are sometimes known as heath balds, referring to the family of plants to which these shrubs belong. The grass balds appear to be grasslands overall with a few clumps of shrubs or stunted trees such as mountain-ash (Sorbus americana) and willows (Salix spp.).
No one seems to know how balds were formed or why they persist. Most natural areas evolve their vegetational composition over time, a process called succession, leading to the ultimate climax community, which would theoretically persist for a long time. At lower elevations in the southern Appalachians, the climax forest would be cove, oak-hickory, or pine forest; at the top of Mount Mitchell, the climax forest is spruce-fir. Yet, on many of the Appalachians' higher peaks are these open, heathlike or grassy bald areas that have not been invaded by the surrounding forest species and have apparently persisted in this state for thousands of years.
Although ecologists have offered many theories for the persistence of balds, no one theory has been universally accepted. Some speculate they could be the result of intermittent fire caused by lightning. Historically, early settlers used balds for grazing cows and sheep, an activity that limited plant succession. Native Americans may have done the same for their domesticated stock. Balds, however, still exist, and probably have not changed significantly for at least hundreds of years.
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