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Invasive Plants at Thrifton Hill Park —What’s the Problem?

Here are some frequently asked questions about invasive plants at the park.

What are invasive plants?

They are plants that have been introduced from other areas of the world, and because of that, they have few natural controls, such as herbivores, parasites, and disease, to keep them in check. They rapidly take over large areas eliminating native plants and the animals that depend on them. They change the composition of the landscape destroying the ecological balance of plants, animals, soil, and water achieved over many thousands of years.  

Why are invasive plants so bad?

Invasive vines kill trees by growing up the trunk and then either blocking out photosynthesis (for a slow death) or weighing them down and making them susceptible to blowing down in winter (for a quick death).  (The picture at right shows english ivy choking trees on the 2700 block of 23rd Road.)  These vines even make it difficult for new seedlings to grow because vines like English ivy provide such a tight layer that sunlight cannot even get through.  As native plants are displaced, animal populations that rely on the plants for food and shelter also decline.  Some invasives like English ivy actually attract invasive animals like rats.  These plant are green, and green is good, right?  No way.  Make no mistake.  These invasive plants are definitely the bad guys.

Invasive plants also:
•    Reduce the space, water, sunlight and nutrients available to native species.
•    Disrupt insect-plant associations that disperse native plant seeds.
•    Reduce and eliminate host plants for native insects and other wildlife.
•    Can host plant pathogens that infect and damage desirable native plants.
•    Increase the incidence of plant disease and stress in forested areas.
•    Make animals sick.  English ivy berries, for example, for some birds vomit further spreading the seeds.
•   Replace biodiversity turning natural areas into vine "wastelands" or monocultures where only one species is present.  The east end of Thrifton Hill Park (near Lorcom Lane and Spout Run Parkway) has already reached this point with porcelainberry taking over (see below).

What invasive plants are taking over Thrifton Hill Park?

Terrible Trees -- tree-of-heaven, princess tree, white mulberry, norway maple, bradford pear
Sinister Shrubs -- bush honeysuckle, multiflora rose, wineberry
Vengeful Vines -- porcelainberry, oriental bittersweet, english ivy, japanese honeysuckle, kudzu, periwinkle, mile-a-minute
Horrific Herbaceous -- golden bamboo, mugwort, japanese (aka bunchy) knotweed, garlic mustard, chinese yam, gill-over-the-ground, oriental ladysthumb

Many of the above descriptions are from Plant Invaders of Mid-Atlantic Natural Areas by the National Park Service and the U.S. Fish and Wildlife Service.  This booklet is a great way to start learning about common invasive plants in our area.

What is the long-term plan for managing invasive plants at the park?

Since Thrifton Hill Park is so overrun with invasives, their removal will be long-term project requiring many years to get them under control.  One of the best ways to reduce invasive plants is to have a sustainable tree canopy, which shades out many highly invasive vines.  Then, moderately invasive vines like English Ivy and periwinkle can be pulled out.  Once invasive are better controlled, the park will regularly need to be monitored and have invasives removed before they spread.

Starting August 2006, Invasive Plant Control Inc. removed and applyied herbicide treatments to invasive plant species in two areas of the park -- the area to the right of the main entrance and the area along the sound wall between Fillmore and Edgewood Streets.  This is funded through a Neighborhood Conservation Grant and includes a retreatment during the summer of 2007.

The Maywood Community Association's (MCA) Parks Committee is working with Arlington County's Park Service and Invasive Plant Program to create an invasive plant control plan and a tree planting plan to remove invasive plants and achieve a better shade canopy.  These plans will be achieved through Arlington County Park Service, Invasive Plant Program, and volunteer efforts.  Arlington County Park Service expects tree planting efforts to begin in late September or in October.  Volunteer invasive removal efforts will take place during park cleanup days.

MCA Parks Committee also hopes to secure future county grants.  In May 2007, we can apply for a Park Enhancement Grant (up to $12,000) to help with invasive removal efforts.  Unfortunately, the Neighborhood Conservation (NC) program has placed a moratorium on new NC grants for two years because of past overruns.  Maywood received an $80,000 grant in 2004, so it is uncertain when we would next qualify for more funding at the park.  MCA needs to update the Maywood NC Plan and establish invasive plant control at Thrifton Hill Park as a top priority to even consider future NC funding.

What improvements can I expect to see once invasive plants are better controlled at the park?

You should see:

•    More trees.  Arlington County Park Service will be able to plant trees once areas are free of the invasive vines that could kill new trees.

•    More new tree seedlings and saplings.  With the dense cover of invasive vines removed, there will be room for seedlings to sprout, grow into saplings, and mature into healthy trees that provide shade canopy and improved air quality.

•    Healthier plants.  Once established in an appropriate area, most native plant species are hardier than exotic plantings and do not require watering, fertilizers, pesticides, or intensive pruning.

•    More native wildlife.  Native plants will have an opportunity to thrive providing wildlife with familiar sources of food and shelter.   In developed areas like Arlington, urban nature parks like Thrifton Hill Park provide essential shelter for displaced wildlife and nesting areas for migratory birds.

•    Less rats and mosquitoes.  English ivy forms the perfect hiding places for urban rats and moist habitat for mosquitoes.  Once english ivy is gone, they do not have the habitat they are looking for.

•    Less erosion.  English ivy's shallow root system increases the likelihood of erosion and slope failure.  With invasive removal, erosion is a concern since native plants needs some time to get established.  Planting suitable native plant communities and mimicing nature being allowing leaves to matt down will help secure soil and minimize erosion.

What can I do to prevent invasive plants from spreading into natural areas?

You can:

•    Keep english ivy down.  from climbing up trees, houses, walls, or other vertical surfaces where it starts producing berries that birds then spread and where it kills trees.  For practical advice on how to remove English ivy, see the brochure by Arlington's Invasive Plant Program.
•    Plant native.  Do not purchase or use invasive exotic species in your yard.  Use plants that are native to your local region or those that are not invasive.  If you are unsure of the identification of a plant, take a sample to the Nature Center or Master Gardeners.  To be on the safe side, if you don't know it, don't grow it.  Some nursery also carry  exclusively native plants, saving you the effort of researching.  Local native plant nurseries include: Nature By Design in Alexandria and Earth Sangha (plants are free, but monetary donations are appreciated) in Springfield.  For more sources, see the Native Plant Nursery Directory.
•    Control invasive plants in your yard by removing them entirely or by prevent their spread outside your property. This may include pruning to prevent flowering and seed dispersal or cutting, mowing or herbicide use to prevent vegetative spread.

Where can I find more information?

Virginia/Local:

Arlington County's  Invasive Plant Program - Volunteers and Arlington Staff work to control invasive plants at more than 30 Arlington County sites.  Learn more about the program and see work site photos at:
http://www.arlingtonva.us/Departments/ParksRecreation/scripts/parks/ParksRecreationScriptsParksInvasive.aspx

National Park Service and U.S. Fish and Wildlife Service's Plant Invaders of Mid-Atlantic Natural Areas is a great booklet describing common invasive species and native plants to use in their place.  A must have for fixing up your yard or the park!
http://www.invasive.org/eastern/midatlantic/ 

Native Plants for Wildlife Habitat and Conservation Landscaping
Chesapeake Bay Watershed is a more detailed guide to native plant alternatives with good pictures.
http://www.nps.gov/plants/pubs/chesapeake/index.htm

Mid-Atlantic Exotic Pest Plant Council 
http://www.ma-eppc.org/ 

Virginia Department of Conservation's Invasive Plants of Virginia.  They have a invasive plant species listing that ranks how invasive certain plants are (highly, moderately, occasionally).
http://www.dcr.state.va.us/dnh/invlist.htm 

Native Plants for Conservation, Restoration, and Landscaping in Virginia
http://www.state.va.us/dcr/dnh/native.htm

National/Other Areas:

Southeast Exotic Pest Plant Council Invasive Plant Manual 
http://www.invasive.org/eastern/eppc/

Silent Invaders by the U.S. Bureau of Land Management with movie clips that make it really easy to understand how invasives take over, their impact, and what to do.  Great for kids and adults.
http://www.fsu.edu/~imsp/silent_invaders/new_weeds/main_html/

“Invasive plants are killing native trees” -- look at "How invasive ivy kills" a short animation of English Ivy killing a tree
http://seattlepi.nwsource.com/local/247350_urbanforest07.html

Weeds Gone Wild Home Page                                 http://www.nps.gov/plants/alien/

Center for Invasive Plant Management
http://www.weedcenter.org/education/edu_overview.html

A good background on invasive species
http://en.wikipedia.org/wiki/Invasive_species