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Perched dunes share the
foredune, blowout, backdune forest, and interdunal wetland found on the
parabolic dunes, and most of
the discussion of these zones under parabolic dunes is relevant to the
perched dunes as well. Many of
the rare plants and animals of the parabolic dunes, including Pitcher’s
thistle, Lake Huron tansy, clustered broom rape, and the Lake Huron locust
are also common within
the perched dunes. Two rare plants that are especially common on the
perched dunes are
dunewort and clustered broom rape, both disjunct from the western United
States.
Beaches associated with
perched dunes, lying beneath steep, eroding bluffs, are often much narrower
than their parabolic dune counterparts. During periods of high Great Lakes
water levels, the lake’s
water can be directly eroding the bluffs. Even though the beaches can be
quite narrow, piping
plovers are known to nest on the beaches below the perched dunes, as at
Sleeping Bear Dunes
National Lakeshore.
Steep eroding bluffs of
till form the base from which the perched dunes rise. For both the Grand
Sable dunes on Lake Superior
and the Sleeping Bear dunes on Lake Michigan, the bluffs are responsible
for roughly 300 feet of elevation, while the perched dunes formed on the
bluff are only half
that height.
On some bluff faces
fine-textured banding results in numerous seepages. Trees and shrubs
establish on the bluff
faces, but continual erosion of the bluff base results in widespread
instability.
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