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The use of the
term Southeast denotes the southeastern
United States.
Circumboreal
species occur around the globe in boreal
communities, which are generally limited to northern latitudes or
at successively higher elevations as one journeys toward the equator.
In the Blue Ridge, boreal zones are found at higher
elevations, from about 4000' to the 6684' limit of our highest
peak.
Middle
elevations lie within 2500 to 3800' elevation, and lower
elevations in the Blue Ridge include elevations of 1000 to 2500'.
Foothill, intermountain hill, valley and bottomland forest communities
are all found in lower elevations.
Bogs and cove
forest communities may be found at any elevation, but species composition
varies greatly with the elevation and soil condition.
The acidity
of soils (measured by pH) greatly influences mountain vegetation.
Where pH is low (acidic), ericaceous understory plants and canopies
of oak. birch, and conifers are characteristic. Such acidic sites
may be seen on steep slopes, high elevations, acidic coves, and
in most bogs.
Where acidity
decreases (pH rises), the soil becomes "sweeter" or "rich" (these
being common language terms used by settlers) and supports more
diverse vegetation. The soil may become circumneutral
or basic when pH rises from 6.0 to
7.0, such as in some rich coves, or in soils overlying rock substrates
which act to raise pH. Some forms of granite, hornblend gneiss,
or calcareous rock like limestone tend to affect overlying soils
in this manner. Calcareous soils and limestone outcroppings are
much more common on mountain provinces and escarpments west of the
Blue Ridge.
Classifications
of soil moisture levels range from xeric
(dry) to hydric (wet). Mesic
sites exhibit a relatively stable intermediate moisture regime,
and these moist areas often produce some of our most attractive
forests. Soil moisture levels are affected by the depth and physical
structure of the soil, by the degree and duration of direct sunlight
during the day (exposure and aspect
of topography), and by the steepness and drainage rates of the topography.
Most plant species
are more successfully adapted to certain moisture regimes, and are
indicators of such conditions
when they are abundant in a natural community.
Plants tolerant
of shade are able to grow below the canopy for a large part of,
or all of their life cycle. Understory
species remain tolerant of shade through maturity. Intolerant
species need direct sunlight and do not reach maturity if shaded
by other species. These by necessity tend to be canopy
species.
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