By Steven L. Stephenson
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Extra info for A Natural History of the Central Appalachians
This is most apparent in the Ridge and Valley province, where a ridgetop and the floor of an adjacent valley may be separated by a distance of less than a mile but represent two very different FIGURE 22 Three-lobed bazzania, a liverwort that sometimes forms an almost complete cover on the forest floor in some high-elevation red spruce forests 0 3 PLANT LIFE OF THE CENTRAL APPALACHIANS often conspicuously absent or, in some years, represented for a short period by a large number of newly germinated seedlings, the majority of which fail to survive.
The primary reason for this seems to be the smothering effect of the blanket of dead leaves that accumulates as a result of leaf fall. The dead leaves easily slide off the elevated substrates. When the various layers of vegetation in a forest dominated by conifers are compared with those of a forest dominated by broadleaf trees, major differences are apparent. For example, in a mature conifer-dominated forest the canopy layer is well developed, and the individual canopies closely intertwined. The dense shade cast by such a canopy often means that lower layers of vegetation show little diversity: the understory tree and sapling layers sometimes consists of only a few scattered individuals.
Although today much of the region is well above sea level, this was not always so. For many millions of years the landscape of the Central Appalachians was the bottom of a shallow sea, and the inhabitants were marine organisms, some of which are well represented as fossils. Later the region supported what have become known as coal swamp forests, which were dominated by treesized plants that are now extinct but left behind evidence of their presence in the form of coal. 6 million years the Central Appalachians have experienced what are known as the ice ages, characterized by the presence of large mammals known as the North American megafauna.