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We are not
talking about a pond (open water), nor a swamp (lowland forest), nor
a wet sedge meadow (dry marsh, wet only in spring), nor a bog (a
floating complex of acid peat moss with tamarack trees).
We mean the
region of gradual transition between land and deep water--the more
gradual the better, and the more irregular, the better.
Gradual
shallow shores, interrupted by islands caused by an uneven bottom
and by muskrat houses, create an
ever-changing
pattern
of
shallows and
deeps which
continually renews life, yet concurrently maintains all stages of
marsh development and wildlife. Diversity is greatest because no
plant
or animal becomes a too-abundant pest.
Diversity is
also greatest because a variety of animals and plants can live in
these ever-changing shallows, the environment closest to the
shallow seas
where life began on earth some 3 billion years ago. This tiny
example will exhibit most of the species found in shallow and deep
freshwater marshes, and some of those of the pond and sedge meadow
as well.
Maintaining a
healthy marsh depends on natural gradual cycles involving water
levels, muskrats, and vegetation. The normal summer low permits
annuals like arrowhead, smartweeds and bur-marigolds to grow and
feed birds, and, exposes mud for feeding migrant shorebirds, but
comes too late
to let coons
reach the June nests. The normal high
of
fall through spring attracts migrant waterfowl, permits safe
wintering of frogs, turtles,
fish and
muskrats, and encourages breeding of plankton, frogs, and birds in
the spring.
Over the
years, climatic cycles cause important lows and highs also.
Emergents like cattail may get too dense unless flooded out in high
years or killed by "highs" of muskrats; but then they cannot restart
except in occasional summers of very low water. Muskrats may not eat
enough
openings in the cattail if winterkills, mink or trapping reduce
their numbers too much. Then the cattails may get so dense as to
favor too
many
muskrats, causing an "eat out", which only a dry summer can restore.
Careful
management of water levels here may prevent extremes of water depth,
cattails, or muskrats; but timely moderate gradual fluctuations
are
healthy. The survival of each species depends on the improved
adaptation made possible by continual replacement in each population
of
individuals.
Can you
see
a
muskrat house from where you stand?
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