| Following
hurricanes Katrina and Rita, initial assessments of Louisiana’s
coastal ecosystems indicated extensive marsh losses and
damage to the coastal environment. Satellite photos are
showing that more than 13,000 square acres of coastal wetlands
and a number of offshore barrier islands in the Gulf of
Mexico have disappeared entirely.
While
assessing the actual land losses and damage and its economic
impact to the state is difficult, what’s more difficult
is estimating the long-term effects to the health of the
coastal ecosystem.
Louisiana’s coastal marshes are in a continuous state
of evolution. They change over long periods time. In most
instances, so slowly, that the changes are barely noticeable.
Since
plants are the primary producers in most ecosystems, they
provide the first indication of ecosystem metamorphosis.
Scientists call this change plant succession. Plant succession
is the process in which plant communities replace one another
over time until they reach what is called a climax community.
For example, the series of changes which take place from
a few small grasses growing on bare rock to the establishment
of a forest may take many decades or centuries. Plant succession
in Louisiana’s marsh ecosystem happens much more quickly
than that.
The
first stage is shallow, open water which receives some water
exchange through drainage flow or tidal movement. These
water movements carry sediments and nutrients necessary
for plant growth. When water clarity allows sunlight to
penetrate the water column, submerged aquatic plants will
sprout and begin to grow. Once these plants grow thick enough
to trap enough sediments and organic matter to form mats
which reach the water’s surface, grasses will grow.
The grasses mat up and form larger, semi-aquatic land areas
where larger emergent plants grow and eventually evolve
into woody plants and trees.
This
is a long, slow process and in many areas of coastal Louisiana
was occurring in reverse order of the natural succession
described here, thus causing land loss.
It
is important for coastal landowners and managers to recognize
where their marshes were in this succession process in order
to assess damage and make management decisions for remediation
and recovery after the hurricanes’ damage. In the
most extreme cases, healthy, vegetated marshes were reverted
to open water. Scientists refer to this as setting back
succession. Setting back succession is sometimes not a bad
thing and actually promotes increases in production.
Landowners and managers sometime initiate setting back succession
under controlled situations through saltwater introduction,
herbicide applications or burning. It is a method used to
maintain and promote productivity of coastal marshes. However,
the 2005 hurricanes have done this for us on a large scale
and the effects will be measured for years to come.
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