Analyses using Remote Sensing Technologies
Much of the suns energy
that reaches the earths surface is reflected back into space.
This includes not only the red through blue colors of visible light
but also nonvisible parts of the spectrum of electromagnetic radiation
such as ultraviolet and infrared energy. Since the 1970s, satellites
have been monitoring this reflected energy, forming images of the
earths surface, and returning the images to earth-based receiving
stations. The scientific discipline of remote sensing involves the
processing and analysis of these images to map, detect, and quantify
changes in the earths surface.
Satellite images, such as the
one shown below, clearly show the contrast between the forested Savannah
River Site (SRS) and the surrounding, largely agricultural area. The
predominance of forests on the SRS appears as broad areas in shades
of bright green. Bare soils, fallow fields, crops, and abandoned farmland
in the surrounding area are relatively small patches of white, faint
blue, lime green and maroon, respectively. Although the image provides
a qualitative comparison of habitats and land uses between areas on
and off the SRS, it is not as informative as the quantitative comparisons
that can result from remote sensing technologies. Such a quantitative
comparison may indicate less obvious but potentially important differences
that can affect decisions on management and steward-ship of SRS lands.
To obtain a quantitative comparison
of on-site and off-site areas, the staff of the Savannah River Ecology
Laboratory (SREL) used remote sensing technologies to analyze a series
of four Landsat Thematic Mapper (TM) images from 1997 and 1998. These
images contain measures of reflected electromagnetic radiation in
visible and infrared bands for 30-m by 30-m units of ground surface,
called pixels. The four images were selected from different seasons
to ensure accurate mapping of pines, deciduous hardwood forests, abandoned
farmland, pastures, and both early-season and late-season row crops.
A 100-km by 100-km area centered on the SRS (below) was mapped into
the following habitat and land use classes: urban/industrial; bare
soil; herbaceous vegetation such as that on abandoned farmland or
recently cleared forests; row crops; managed grasslands such as pastures,
lawns, and golf courses; short-stature scrub forests; open canopy
pine forests which are indicative of older pine forests; dense canopy
pines which are indicative of young, more recently established pine
plantations; upland forests of deciduous hardwoods; floodplain hardwoods;
swamp forests; water; and marshes such as those in Carolina bays.
Comparisons of the distributions of these habitats and land uses between
the SRS and surrounding areas indicated differences that could be
attributed to (1) initial constraints on the placement of the SRS,
(2) past management of the SRS, and (3) recent management of pine
forests on surrounding lands.
and Water are More
Abundant on the SRS
Relative distributions of habitats
and land uses on the SRS and in surorunding off-site areas.
Floodplain hardwoods are 20%
more prevalent and swamp forests are 100% more prevalent on the SRS
than off-site. This results from the regions geomorphology and
the initial constraints placed on locating the SRS. Because of the
need to use and discharge large volumes of water for reactor cooling,
the SRS was placed adjacent to the Savannah River, on land dissected
by relatively large creeks that were used to return water to the river.
The abundance of floodplain forests was further enhanced by the inclusion
of the floodplain of Lower Three Runs Creek in a narrow corridor of
the SRS. Water is twice as abundant on the SRS because of the construction
of reactor-cooling reservoirs such as Par Pond and L-Lake. Most of
the off-site water bodies are small farm ponds, Carolina bays, and
the Savannah River. The large SRS reservoirs provide important winter
habitat for migrating waterfowl.
The SRS has
More Abundant, Older Pine Forests than the Surrounding off-site Area
Pine forests are more than
twice as abundant on the SRS, which is the most obvious difference
between the SRS and surrounding areas. This difference occurs because
land management on the SRS included planting of pines in the early
1950s on areas that had been row crops, managed grasslands, and old
fields of herbaceous vegetation before the site was established. Some
managed grasslands still occur on the SRS as lawns around facilities
and as vegetation covers for waste burial sites, and herbaceous vegetation
still occurs along power lines, water lines, and on recently cut forest
Cutting of 1974 pine
forests in areas surrounding the SRS and their replacement
with newly established pine plantations.
Although this difference is
obvious, recent changes in forest management in the surrounding area
have resulted in subtle changes in the relationships between SRS forests
and those on private lands. Since
the mid 1970s, the off-site pine forests that had established on farmland
abandoned in the 1920s and 1930s have been extensively cut. By 1997,
more than 75% of the off-site pine forests that existed in 1974 had
been cut. The establishment of pine plantations on off-site areas
also increased in the 1980s.
In 1974, the SRS was mostly
young, recently planted pine forests, while the surrounding area was
mostly older pine forests established in the 1920s and 1930s. Now
the SRS has mostly older pine forests, while many of the surrounding
off-site pine forests are younger, recently planted stands. This marked
difference between the SRS and the surrounding region highlights the
importance of this 310-square mile site to the biodiversity of the
southeastern U.S. Because less than 10% of the SRS is developed or
used by the Department of Energy (DOE) for industrial sites, waste
containment, and infrastructure such as roads and power lines, the
remainder of the site is managed for timber, forest products, and
wildlife, or set aside in "control" areas that remain relatively
undisturbed. This has resulted in this site becoming a center of biodiversity
in the Southeast.
The SRS preserves not just
plant and animal species, but also large tracts containing important
habitats that have become increasingly rare off-site as lands are
farmed, harvested, or developed. Furthermore, the SRS provides for
relatively long-term, predictable preservation of these habitats.
This contrasts with the surrounding area where lands are broken up
into relatively small, privately owned parcels whose fates are often
affected by unpredictable changes in demands for agricultural products,
forest products, and space for urban expansion. As plant and animal
species and their respective habitats become increasingly threatened
across the Southeast, remote sensing technologies will continue to
be important in assessing the SRSs role in the regional management
of biodiversity and natural resources.
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