tidal hardwood swamps - Maryland Department of Natural Resources

DISCUSSION
Site Visits
During the landscape analysis for this project, 227 potential sites were identified for assessment. The
most productive method used to determine these sites was analyzing digital orthophotography in
conjunction with National Wetlands Inventory maps. Several sites were also identified through
consultation with regional ecologists and from de novo surveys. During the field surveys for this project,
approximately 158 of the 227 potential sites were visited for assessment. Approximately 79 sites were
not sampled due to heterogeneous vegetation, small size, degraded habitats, inaccurate NWI signatures,
and time constraints. After a preliminary understanding of forested tidal community types on the Eastern
Shore was established, the need to collect additional data in those types tapered. However, several
weeks were spent collecting plot data from the Western Shore of Maryland. This proved to be extremely
beneficial in understanding the statewide distribution of certain Fraxinus spp. dominated communities.
After the preliminary classification was developed, sites were visited to check this classification and data
was collected only in suspected new community types. As a rule of thumb, between five and ten
vegetation sample plots for each community type are best for an accurate classification. Since this
classification has five community types, the 86 plots are considered ample for their description.
Classification
This project yielded five forested associations found within tidal wetlands of Maryland’s Eastern Shore.
This classification is a product of untangling statistical analyses and interpreting the landscape. These
community types were determined by balancing the results of various classification and ordination
techniques on several versions of collected data with the opinions of project ecologists, regional
ecologists, and regional community classifications. One cannot solely utilize multivariate statistical
methods and expect to determine an ecologically meaningful classification. These statistics are merely a
tool, albeit an extremely powerful one, to assist in the understanding of ecological information. Often
times, these tools cannot accurately examine subtle relationships between generally similar vegetation
types and create groups based on the presence or absence of less ecologically meaningful species.
Through subsequent analyses of these data, it was determined that all of the vegetation types are
influenced by several abiotic factors. The dominant factors that determined the classification of these
vegetation types are salinity, elevation, and frequency and duration of tidal flooding.
Forested Wetland Conditions – Past and Present
Many high quality examples of tidal forested wetlands were encountered on Maryland’s Eastern Shore.
Despite these exceptional examples, several areas on the Eastern Shore suffer from significant abiotic
and biotic threats. Many of these threats have led to qualitative changes in wetland function, structure,
and composition. Agricultural runoff, coastal erosion, upland development, logging, and the spread of
invasive species such as Common reed (Phragmites australis) continue to place pressure on Maryland’s
wetlands. Recently, there has been a sharp reduction in overall wetland acreage loss due to strong
regulation of coastal wetland alterations through Maryland’s Tidal Wetlands Act and through Federal
regulations (e.g., Section 404 program, Section 10 program) pursuant to the Federal Clean Water Act
(Tiner and Burke 1995). Prior to these regulatory measures, most wetland loss was attributed to activities
such as ditching, dredging, and impoundment construction. The effects of chronic, eustatic sea level rise
in the Chesapeake Bay region has been well documented by many researchers. More recently, studies
have centered around the estuarine marshes bordering Blackwater River in Dorchester County. Although
chronic, eustatic sea level rise is thought to be the principal cause of wetland loss in certain areas,
isostatic processes such as crustal plate elevation and local events such as subsidence resulting from
groundwater withdrawal have also postulated to contribute to the phenomenon. Changes in vegetation
structure and composition such as contemporary crown stress and tree mortality due to these suspected
processes are apparent in this area and other parts of the Chesapeake Bay region. Such changes are
believed to be an artifact of salinity gradients shifting upstream in estuarine tidal river systems. This
phenomenon is visible along portions of the Blackwater River where fringing snags and stumps of Loblolly
pine (Pinus taeda) border otherwise healthy forests. On the Potomac River, similar observations of this
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