[to the U.S.] probably every day,” Huebner says. A small number — possibly as small as 1 percent — of non-natives turn out to be villainous. Predicting which ones will be helpful and which will be harmful is a challenge of agency cooperation and research, both at the borders and in the field.
In every region where development touches landscapes, invasives follow. “Anything that’s disturbed is more likely to be invaded,” Huebner says. Natural disturbances — a tornado, a fallen limb, a natural treefall — create opportunity for an invasive seed waiting for a patch of sunlight. Human-caused disturbances, such as new trails, roads, or mowing, bring additional opportunities. In contrast, less fragmented wilderness forest tracts stand the best chance of shutting out invasives.
For these reasons, “urban and suburban areas are much more affected than rural areas,” Bergmann says. That’s because most invasives first take hold in urban regions, where vines and shrubs are introduced as landscaping or erosion control, or tracked in as seeds by hikers or vehicles. The plants then spread to nearby natural areas, where visibly distressed forests are enough to call some to arms.
Weed Warriors To The Rescue
The Capital Crescent Trail near Washington, D.C., cuts through a skinny urban forest tract under constant siege. “I don’t want to live in a neighborhood where vines pulling trees down is normal,” says Lynnwood Andrews, as she joins up with other weed warriors early one August morning. In a gorge below the urban trail, mile-a-minute weed grows over dense clumps of porcelain-berry — invasives conquering invasives — a poignant snapshot of ecological anarchy.
Weed warrior coordinator David Brooks is literally up to his waist in invasives.
For weed warrior volunteers, part of the reward is saving a sapling from a net of porcelain-berry, or seeing plots that used to drown in vines begin to host small native bushes again. They also like the fact that they can do something tangible to defend the local forests they love.
On a small scale, such labor-intensive hand-pulling can successfully keep native plants safe while getting to the root of the problem. But knowing the enemy’s seasonal schedule is key. Because of invasives’ long-lasting seed banks, volunteers must wrangle weeds before they go to seed, or hand pulling is useless until next year, when the problem has multiplied.
Though many local parks rely on volunteers to help control invasives in patches, they’re only a small part of our regional and national defense, which managers are piecing together with limited funds.
To someone looking out over an acre cloaked in leafy vines or carpeted in alien grasses, ecological ruin seems imminent. But researchers, foresters, and ecologists are figuring out how to halt the enemy advance. Prevention, they agree, is our best defense.
In Wisconsin, Department of Natural Resources Invasive Plant Coordinator Kelly Kearns is on high alert for stiltgrass, which hasn’t yet spread to that state. She’s implored residents to report any sightings of the invader, so that they can be eradicated immediately. So far, she has been successful at keeping stiltgrass out of state lines.
For a preventive strategy to work, education is key. Teaching homeowners and landscapers how to identify local invasive threats and the risks of planting invasive species (such as barberry, winged burning bush, and English ivy) would help slow the invasives’ advance. Keeping problem plants from spreading also requires careful cleaning of forestry and firefighting equipment, especially tire treads, to prevent spreading seeds to other natural areas.
The second line of defense involves early detection and rapid response. Weed warrior volunteers, cooperative weed management groups, hikers, and hunters can be invaluable in bringing attention to new infestations. At that point — when the invasion is small — hand-pulling can be effective.
This mid-Atlantic forest has been spot-treated with herbicide.
When a nuisance plant becomes established in thick stands, however, agencies and land managers must resort to treatment, which can include integrated pest management techniques, annual mowing, or chemical treatment. For infestations of some species that gain a foothold — such as cogongrass — herbicides are the only option. The most common herbicides, like glyphosate (Roundup) or triclopyr (Garlon), kill all that’s green, but new grass-specific herbicides target just the grasses and leave other plants alone.
During treatment, the biggest mistake that forest managers can make is to remove invasives but ignore the next steps: re-treating an area in subsequent years, and replanting the native species. “You may end up in a money pit or make the problem worse,” says Huebner, unless you stick with treatment for years. Over time, infested acres can be returned to their natural state.
Still, we’ve much to learn. How to stop invasive plants from spreading is a topic that the U.S. Forest Service and other agencies are grappling with, Miller notes.
Better laws would help. Some states, such as Washington and Oregon, have state noxious weed laws, which require the removal of certain problem invasive species on both private and public properties. Better cooperation between landowners would strengthen our defenses, too. There’s often a gray area regarding who has responsibility for marginal lands bordering highways and railways, where invasives tend to thrive.
Meanwhile, anyone who cares to defend local forests can join the invasive-fighting ranks by learning what enemy plants look like, gearing up in leather gloves, and squelching local invasive uprisings.
– Carrie Madren writes from Olney, Maryland, and can be reached at firstname.lastname@example.org.
Read More: Kudzu’s Climb To Infamy
This article was published in the Winter 2011 issue of American Forests magazine.