Michigan Forest Communities - Michigan Association of ...

Part III.
Open-Canopy Upland Forest
Communities
Open forests of scattered or
clumped trees—known as
savannas or barrens—represent a
transition between closed forests and
prairies. They are maintained by frequent
disturbances, usually fire or
grazing. Trees are the dominant
structural feature, but their low density
and dispersion allow many
plants typical of prairies and meadows
to occupy the large gaps in the
overstory. Forest understory species
are more common in shaded areas.
Although they occupied more than 2
million acres in the early 1800s,
savannas are the rarest forest communities
in Michigan today. In fact,
the bucolic upland “oak openings”
described by early settlers and by
James Fenimore Cooper in his story
of the same name have disappeared,
as have the prairie chickens that
occupied them. Because many
savannas—particularly oak openings—occupied
fertile mesic habitats,
they were long ago cleared for
agriculture. Many wet-mesic savanna
habitats were drained or grew into
closed forests. Urban development
also claimed much of the area once
occupied by open forests. Savanna
communities in xeric habitats
unsuitable for farming grew into
closed forests when fire was excluded
or when farmland was abandoned.
Today state, federal, and private
agencies are actively working to
preserve or restore examples of
these fascinating communities.
Open communities also can be
the product of harsh habitat conditions
(e.g., rock outcroppings) or
human disturbances. Although these
communities also are relatively rare,
their total area in the state has
remained fairly stable or slowly
declined since Euro-American
settlement.
W
L
R
= widespread; type very common in one or several regions or
throughout the state, with many examples close at hand.
= local; type confined to a specialized habitat in a particular region
or regions of the state, yet not hard to find.
= rare; type very uncommon and highly localized in the state, with
very few examples.
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