Vegetation Classification and Mapping Project Report - USGS

USGS-NPS Vegetation Mapping Program
Colonial National Historical Park
The regional analysis of alluvial forest sample plots is illustrated in Figures G17-G19 of
Appendix G. Plot samples cluster into three compositionally distinct groups in both the
dendrogram and the two-dimensional ordination. Plot samples segregate along axis two, which
represents 77% of the variance in the data (Table 10). The joint plot (Appendix G, Figure G19)
shows the correlation of soil fertility variables with axis two of the ordination, suggesting that
soil nutrients have an important influence on vegetation patterns within this group. The 48 plot
samples representing the only alluvial forest association found at Colonial National Historical
Park, Coastal Plain / Piedmont Small-Stream Floodplain Forest (CEGL004418), are at the low
end of the soil fertility gradient (Appendix G, Figure G19) and have the lowest averages in the
group for soil variables indicative of fertility (Appendix F, Table F2). Coastal Plain / Piedmont
Small-Stream Floodplain Forest develops over acidic soils along small streams in the Coastal
Plain of Maryland and Virginia and west across the Virginia and North Carolina Piedmont to the
Cumberland Plateau and Ridge and Valley. Piedmont / Mountain Alluvial Forest
(CEGL006492) is found on small to medium sized streams over more fertile alluvium, while
Piedmont / Mountain Floodplain Forest (CEGL006217) is found on the large floodplains of
major mid-Atlantic rivers over the most fertile alluvium (Appendix F). A compositional
summary of Coastal Plain / Piedmont Small-Stream Floodplain Forest is presented in Appendix
H, Table H9. The single plot sample from Colonial National Historical Park is representative of
the association, with all the nominal species and many of the constant species. This association
is found in four of the seven national parks in this study (Appendix D).
The classification of 70 swamp forest sample plots is illustrated in Figures G20-G22 of
Appendix G. Plot samples cluster into two compositionally distinct groups in the dendrogram
and into two less distinct groupings in the three-dimensional ordination (Appendix G, Figures
G20 and G21). The joint plot shows strong correlations of soil fertility variables with axis three
of the ordination, suggesting that soil nutrients have an important influence on vegetation
patterns within this group (Appendix G, Figure G22). Plot samples classed as the only swamp
forest association present at Colonial National Historical Park, Coastal Plain / Piedmont
Floodplain Swamp Forest (Green Ash - Red Maple Type) (CEGL006606), are at the high end of
the soil fertility gradient (Appendix G, Figure G22) and have the highest averages in the group
for soil variables indicative of fertility (Appendix F, Table F2). These forests also tend to have
longer hydroperiods and deeper flooding than forests classed as Coastal Plain / Piedmont
Floodplain Swamp Forest (Mixed Oak - Red Maple Type) (CEGL006605), although these
variables were not measured directly. The two plot samples from Colonial National Historical
Park are compositionally typical of the association (Appendix H, Table H10), with all nominal
species and many of the constant species. In this study, Coastal Plain / Piedmont Floodplain
Swamp Forest (Green Ash - Red Maple Type) was only found at Colonial National Historical
Park.
The nonriverine forest group is presented in Appendix G, Figures G23–G25. Plot samples from
62 nonriverine forest plots cluster into four compositionally distinct groups in the dendrogram,
the two-dimensional ordination, and the three-dimensional ordination (Appendix G, Figures
G23–G24). In terms of species composition, the associations show the greatest separation along
axis two of the ordinations (Table 10; Appendix G, Figure G25). Ordination scores were not
significantly correlated with available environmental data; however, as a group, these forests
have low values for soil chemistry variables, indicating acid soils with low fertility (Appendix
F). Three of the four associations occur at Colonial National Historical Park, Coastal Plain
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