St. Marks NWR Comprehensive Conservation Plan - U.S. Fish and ...

plants) or mobile sources (e.g. automobiles, planes, trucks, buses, and trains). There are also
natural sources of air pollution, such as fires, dust storms, volcanic activity, and other natural
processes. The Agency has identified six principal pollutants that are the focus of its national
regulatory program: lead, carbon monoxide, ozone, nitrogen dioxide, sulfur dioxide, and particulate
matter.
Air pollution causes damage to the environment and property and affects human health. Both federal
and state governments track air quality and visibility impairment, through a system of 5,200 monitors
at 3,000 locations across the United States. Florida has 227 monitors at 141 sites. Carbon
monoxide is from combustion or fire sources and is a problem mainly in cold weather climes. Lead
has not been detected above standard levels, except in places that have a smelter source. Nitrogen
dioxide is only monitored in large metropolitan areas, but Florida has never approached the standard.
Sulfur dioxide is emitted from power plants and paper mills. None of these four principal pollutants
are monitored near the refuge since they are not considered problem pollutants in this area.
The Clean Air Act provides for the protection of visibility in national parks and wilderness areas, also
known as Class 1 areas. A visibility station for monitoring airborne particulate matter was established
on the refuge in June 2000. In April 2001, an ozone monitor was also installed. From the data
collected since that time, the 85 parts-per-billion standard for ozone over an 8-hour period has been
exceeded only twice, on May 14 and 16, 2001.
BIOLOGICAL ENVIRONMENT
NATIVE VEGETATION/PLANT COMMUNITIES/FLORA
The refuge encompasses more than 43 miles of coastal salt marshes backed by hardwood swamps,
hardwood hammocks, and upland pine communities within Florida=s Big Bend region. The dominant
forces affecting vegetation characteristics are minor elevation changes, fire history and current fire
management practices, historical timber harvest, and current timber management practices.
While elevation on the refuge ranges from sea level to 45 feet, subtle changes in topography result in
substantial vegetation differences. Historically, frequent low-intensity fires burned the uplands every
1 to 8 years, resulting in a classic mosaic of longleaf and slash pine-dominated flatwoods and
sandhills on the refuge=s uplands. Prior to refuge acquisition, much of the original growth of pine and
cypress was commercially harvested for lumber. Subsequent to refuge acquisition in 1931,
approximately 1,900 acres of brackish and salt marshes were enclosed by levees and water
management structures. These areas, formerly dominated by salt-tolerant marsh vegetation, now
support a diverse assemblage of freshwater and brackish emergent, aquatic, and floating plants,
including sedges, rushes, spikerushes, cattails, water lilies, and widgeon grass.
The refuge contains examples of 24 natural communities as defined in the Florida Natural Areas
Inventory (FNAI) Guide to the Natural Communities of Florida (1990). In 2005 the refuge completed
an in-house Geograohic Information Systems (GIS) project to map the natural vegetation
communities within the refuge, based on forest stand inventory data from the Forest Management
Plan (1985) and corrected upon Digital Ortho Quarter Quad (DOQQ) aerial imagery from 1999
provided by the Florida Department of Environmental Protection. Discrete habitat units were
delineated at a scale of less than one acre (38 percent of 5,969 polygons are from .01-.99 acres in
size). Minimal ground truthing was employed during this phase, since the primary effort was to
digitize available data. Forested habitats had already been assigned habitat descriptions that were
easily matched to the FNAI’s Guide to the Natural Communities of Florida. Nonforested areas of the
refuge, primarily coastal marshes and associated habitat types, were relatively easy to distinguish
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St. Marks National Wildlife Refuge