Michigan Forest Communities - Michigan Association of ...

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Alvar Savannas
R
Habitat
Alvars consist of flat, calcareous
(limestone and dolomite) bedrock pavements
lying close to the shores of the
Great Lakes. They are harsh habitats,
typically quite wet in the spring but
excessively dry by late summer. This
yin and yang of moisture is central to
alvar ecology. The thin alkaline soils are
deepest and bedrock is less exposed
away from the direct wave and ice
action of the lakes. Disjunct prairie
communities tend to occur where
bedrock lies at the surface and soils are
thinnest (Catling and Brownell 1999).
Plants tend to grow in fissures in the
fractured rock, sometimes creating
striking linear assemblages. Open
savannas or patches of trees up to several
acres in size intermingle with the
prairies. Where soils are well developed,
closed cedar-dominated boreal forests
grow. Late-season fires were once a factor
in these habitats, but today fire prevention
and suppression have excluded
this ecological process.
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