Vegetation Classification and Mapping Project Report - USGS

USGS-NPS Vegetation Mapping Program
Colonial National Historical Park
herbicide application). Since the species can germinate following early-season removal, removal
two or more times a season to more quickly deplete the seed bank has shown promise as a
technique for discrete, high-priority sites (The Nature Conservancy, Maryland Field Office,
Invasive Species Biologist, Mary Travaglini, pers. comm. 2007). Twelve species of fungi and
eight arthropod species are reported as natural enemies of Nepalese browntop in Asia, but no
biological controls are currently available in the United States (Zheng et al. 2006). Eradication
of the species from large sites where it is well established is not a realistic goal with the tools
now available. However, reducing populations to manageable or non-invasive levels, especially
in rare habitats and vegetation types, should be a high priority for the National Park Service.
While not a long-term solution, keeping Nepalese browntop in check while more effective
biological controls are developed is the best strategy available at present and is critical to
avoiding drastic declines in biodiversity and forest health in the near future. Both mechanical
and chemical controls may be used to combat infestations of common reed. Mowing, flooding,
and prescribed fire in combination with successive herbicide treatments have all been shown to
be effective against this invasive perennial grass (Thompson et al. 1984, Caffrey 1996, Kay
1995, Monteiro et al. 1999). European insects that feed exclusively on common reed are being
evaluated for their potential as biological control agents, but any practical tools are years away
from being available (Tewksbury 2002). Herbicides that contain glyphosate or imazapyr, applied
to actively growing plants, are the most effective method for controlling extensive invasions of
common reed. Both chemicals are available in formulations that are approved for use in wetland
habitats.
Small patch communities occurring over fertile, calcareous substrates are the most susceptible to
exotic species invasions. Coastal Plain Calcareous Seepage Swamp, Coastal Plain Mesic
Calcareous Ravine Forest, and Coastal Plain Dry Calcareous Forest are some of the rarest natural
communities in the mid-Atlantic region and should be targeted for monitoring and control of
invasive, nonnative species. Future invasions may be controlled by ensuring that there are
adequate, undisturbed woodland buffers surrounding occurrences of these communities.
The significant wetland community at Green Spring is saturated by groundwater discharged from
the base of slopes on the north edge of the wetland. Maintenance of requisite habitat conditions
requires protection of upslope hydrologic recharge zones and sufficient buffer to ensure the
quality and quantity of both groundwater seepage and surface water. Clearcutting, site clearing,
road construction, and other development actions are potential sources of groundwater
perturbation, erosion, run-off, and siltation which could threaten this community Protection of
the land upslope of this community and south of Monticello Avenue should be a priority for park
managers. Nepalese browntop was observed with low cover in the Non-Riverine Saturated
Forest at Green Spring. Monitoring and control of this invasive grass should be a priority in this
rare and threatened wetland community.
84