Vegetation Classification and Mapping Project Report - USGS

USGS-NPS Vegetation Mapping Program
Colonial National Historical Park
association in this group, Inner Piedmont / Lower Blue Ridge Basic Mesic Forest
(CEGL006186), is known from steep rocky sites of sub-montane landscapes in the western and
northern Piedmont and on lower slopes of the Blue Ridge. All associations in this group have
high soil fertility relative to all other upland forest types (Appendix F), but even within this
group, soil nutrients have a strong influence on vegetation pattern. Axis one of the joint plot
(Appendix G, Figure G13) is highly correlated with the joint plot vectors representing pH,
calcium:magnesium ratio, and fertility index. In the context of this ordination, plot samples
representing the calcareous forests at Colonial National Historical Park are correlated with the
highest soil fertility values and lower values of Topographic Relative Moisture Index (TRMI).
Coastal Plain Dry Calcareous Forest is known from steep, usually south-facing, erosive ravine
slopes that have cut down into deposits of shells and limesands. Plots classified as this
association have the highest average soil pH values (6.5) and soil calcium (4707 ppm) of any
upland forests in the study (Appendix F). A compositional summary of the association is
presented in Appendix H, Table H7. The six plot samples from Colonial National Historical
Park are compositionally representative examples of Coastal Plain Dry Calcareous Forest. This
association is also found at George Washington Birthplace National Monument, but is not at any
of the other parks included in this study (Appendix D). A compositional summary of Coastal
Plain Mesic Calcareous Ravine Forest is presented in Appendix H, Table H6. Coastal Plain
Mesic Calcareous Ravine Forest occurring on shell substrates may be confused with Coastal
Plain Dry Calcareous Forest, and the two forests types may intergrade on the landscape. Coastal
Plain Mesic Calcareous Ravine Forest is distinguished by the closed forest canopy, the lush forbdominated
herb layer, and by the presence of mesophytic species. The single plot from Colonial
National Historical Park is very representative of the association, with all of the nominal species
and many of the most-constant species. Coastal Plain Mesic Calcareous Ravine Forest has a very
restricted range, known only from four counties around Colonial National Historical Park and the
City of Suffolk in southeastern Virginia. The association is not in any other parks included in
this study (Appendix D).
Classification results for the seepage wetland group are presented in Figures G14-G16 of
Appendix G. Plot samples from 72 seepage wetlands cluster into three compositionally distinct
groupings in both the dendrogram and the two-dimensional ordination (Appendix G, Figures
G14 and G15). Axis one of the joint plot (Appendix G, Figure G16) is highly correlated with the
joint plot vectors representing pH, calcium:magnesium ratio, base saturation, and fertility index,
while axis two is significantly correlated with percent cover of boulders. Together these axes
represent 86% of the variance in the data (Table 10). The only seepage wetland present in
Colonial National Historical Park is Coastal Plain Calcareous Seepage Swamp (CEGL006413).
Plots classified as this association have the highest average soil pH value in the group and very
high levels of base cations (Appendix F). A compositional summary of the association is
presented in Table H8 of Appendix H. The three plots from the park are very typical of the
association, with all the nominal and most of the constant species. Coastal Plain Calcareous
Seepage Swamp is restricted to the bottoms of highly calcareous, central Virginia Coastal Plain
ravines that have cut into Tertiary shell deposits. This association is not found in any of the
other national parks included in this study (Appendix D). The remaining two seepage wetland
associations, Coastal Plain / Piedmont Acidic Seepage Swamp and Southern New England Red
Maple Seepage Swamp, occur at opposite ends the soil fertility gradient (Appendix G, Figure
G16). All three seepage wetland associations are considered either globally rare or uncommon
in the state of Virginia (Appendix D).
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