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Removing Invasive Plants Restores Habitats in Maryland
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by Marc Imlay | 2006

Sierrans tackle projects throughout the state to remove invasive plants and give natives a chance to repopulate.

Non-native invasive species of plants such as English ivy, Japanese stiltgrass and kudzu are covering the natural areas that we in the conservation movement have worked so hard to protect from habitat destruction, erosion, and water pollution.  Just as we are making progress on wetlands, stream bank stabilization, and endangered species, these plants from other parts of the world have crept over 20-90% of the surface area of our forests, streams, and meadows.  Many of us feel demoralized and powerless to combat these invaders that have few natural herbivores or other controls.

The Maryland Chapter of the Sierra Club is establishing a program to provide local groups and public and private landowners with various methods for invasive species removal. We are assisting to develop a major work effort at each site, to remove massive populations of about a dozen species over the next three to five years.  Regular stewardship projects are conducted in all seasons year-round.  A high-intensity effort is followed by lower intensity annual maintenance to eliminate plants that we missed, or that are emerging from the seed bank or migrating from neighboring areas.

 The Chesapeake newsletter announces monthly invasive species removal projects at over 30 sites in Maryland.  Almost all projects started as a result of hands-on workshops conducted by Sierra Club members in Charles and Montgomery Counties.  The Nature Conservancy has also conducted projects for many years.

The Maryland Native Plant Society (MNPS) and the Sierra Club sponsor monthly projects at Chapman Forest, Swann Park, and Greenbelt National Park.  With the Anacostia Watershed Society (AWS), they co-sponsor removal projects in Little Paint Branch Park and Cherry Hill Road Community Park in Beltsville, and Magruder Park in Hyattsville, and provide considerable assistance with other projects.

 This year, AWS brought out 1,075 volunteers at 12 parks, including three stream bank stabilization sites.  Also, AWS integrated invasives-oriented curricula components into our Watershed Explorers/River Habitat environmental education programs, involving 176 students from local schools.

 These sites serve as a visible example of what can be accomplished. Our biggest challenge is to ensure that all the successful projects continue.  Restoration of our native ecosystem is realistic but requires leadership, partnerships, and continuing commitment by volunteers ready to work.

 At least 80% of the natural areas are salvageable by applying a combination of mechanical eradication (digging, pulling, cutting) and carefully targeted chemical control.  We remove all the class 1 and class 2 exotic species, typically 5-20 species, because if you eradicate just one exotic, another may replace it.  Re-vegetation is usually not necessary.  Once the invasives are removed, the natives return on their own to recover the majority of the surface area. 

In the natural areas, we only use carefully targeted, biodegradable herbicides, such as glyphosate and triclopyr, which do not migrate through the soil to other plants.  Instead of spraying invasive trees such as Ailanthus, Norway Maple, and Chinese Privet, we inject concentrated herbicide into the tree, either by basal bark, hack and squirt, or cut stump.  Seedlings are easy to hand pull.  We wait for wet soil after a rain, then loosen the soil with a garden tool such as a four-prong spading fork, so the center of the plant rises perceptively, ready to pull.  

These methods are effective if the initial cover of non-native invasive species is less than 30% of the total plant cover, and are adequate if they cover less than 70%.  At a higher percent coverage, more chemicals are necessary to eradicate the invasives.  Native plant re-vegetation may be necessary, using native species that are not cultivars but are obtained from the wild or from nursery stocks originally collected locally in the wild. There are several mixes that include 12 to 16 herbaceous and shrub species, including nitrogen fixers.

A total of 109 individuals worked 635 hours at 800 acres in Chapman Forest last year.   At the 200-acre Swann Park, we are essentially in the maintenance phase after five years of almost completely eradicating all of the park’s 19 non-native species except for the Japanese stiltgrass and garlic mustard.

 At Magruder Park in Hyattsville, we are re-introducing native plants in order to control potential erosion on a steep slope where a monoculture of English ivy was removed. Local volunteer steward Judith Malionek has been spreading a thin layer of leaves from the site on the few bare areas, and no erosion appears evident.  It is a highly disturbed and isolated park, to which native plants will not return without assistance.  Volunteers have reduced the percentage of non-native cover in this five-acre park from an estimated 80% to 70%.

Join us at any on-going invasive plant removal site around the state. Experience, help, and learn!  Remember our five-year goal: for such invasive plant removal projects to become routine throughout the region, the nation, and the world. 


Marc Imlay is the Invasive Species and Habitat Restoration Chair for the Maryland Chapter

> 2006 Table of Contents


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