Vegetation Classification and Mapping Project Report - USGS

USGS-NPS Vegetation Mapping Program
Colonial National Historical Park
Heritage exemplary natural community occurrence because of its large size and overall high
quality. Areas representing the other 11 natural communities mapped in Colonial National
Historical Park do not meet the criteria to be considered Natural Heritage exemplary natural
community occurrences, but these native plant associations are an important part of the park’s
natural resources and should be targets for conservation and management.
Invasive nonnative plant species are one of the main threats to the native vegetation associations
at Colonial National Historical Park. Thirty-eight nonnative plant species were noted in the
quantitative plots and accuracy assessment observations. The fertile, eroding soils of Coastal
Plain Dry Calcareous Forest supported the greatest diversity of nonnative plant species, where 16
nonnative species were noted. Of the other map classes, wetlands and transitional vegetation had
the highest cover by invasive, nonnative species. The most common and problematic species
include Japanese honeysuckle (Lonicera japonica), Nepalese browntop (Microstegium
vimineum), and common reed (Phragmites australis). Japanese honeysuckle and Nepalese
browntop are particularly troublesome because of their shade tolerance and aggressive growth
habits. These species can be opportunistic invaders of the older, more intact forest communities,
getting a foothold where roads, trails, tip-up mounds, downfalls, and other gap-disturbances have
disturbed mineral soil. Once established, colonies are able to more easily expand or spread into
nearby microhabitats. Common reed is an aggressive, invasive perennial grass that invades tidal
wetlands.
Japanese honeysuckle is especially destructive to native vegetation because of its rapid, twining
growth and dense, semi-evergreen foliage that shades out competitors. The vines frequently
strangle shrubs and tree saplings, and over-grow more delicate herbs in a variety of settings.
Nepalese browntop is the fastest spreading, most problematic exotic everywhere in Virginia
today. Within the past two decades, it has abundantly invaded moist, openly shaded habitats
throughout the mid-Atlantic region, forming monospecific carpets of tangled culms that tend to
crowd out competing herbaceous species (Tu 2000). A recent study strongly suggests that
Nepalese browntop responds to forest canopy disturbances with a sudden increase in biomass
that impedes woody regeneration and lowers overall species diversity and stem densities (Oswalt
et al. 2007). Other studies have demonstrated that once established, Nepalese browntop overruns
native herbaceous competitors and leads to dramatic declines of herb richness within a few
years (Barden 1987, Hunt and Zaremba 1992). Common reed (Phragmites australis) is an
aggressive wetland invader that out-competes native plant species, eliminates diverse wetland
plant communities, and provides little food or shelter for wildlife. It grows in dense singlespecies
stands and forms a thick mat of roots and rhizomes, spreading by seed and rhizomes.
Common reed becomes established in areas where soil is exposed through natural (storms, wave
action) or anthropogenic disturbances (construction, ditching).
Other highly invasive, nonnative species noted in the park include tree of heaven (Ailanthus
altissima), autumn olive (Elaeagnus umbellata var. parvifolia), and Chinese lespedeza
(Lespedeza cuneata). Species noted that are considered moderately invasive by the Virginia
Department of Conservation and Recreation (VADCR 2003) include English Ivy (Hedera helix),
golden bamboo (Phyllostachys aurea), princesstree (Paulownia tomentosa)Canada bluegrass
(Poa compressa), rough bluegrass (Poa trivialis), white poplar (Populus alba), curley dock
(Rumex crispus), and Chinese wisteria (Wisteria sinensis). Species considered occasionally
invasive include orchardgrass (Dactylis glomerata), and common periwinkle (Vinca minor).
82