Our urban woodlands are suffering from foreign invaders that choke out native vegetation and eventually dominate the entire forest floor. The four most common invaders are bush honeysuckle, Japanese honeysuckle, wintercreeper, and garlic mustard. Seeds of these plants can be brought into a healthy woodland by birds that snack on the berries and then fly to a new area and poop, or flood waters picking up seeds from infested areas upstream, and even on our hiking boots as we are out enjoying parks.
Bush honeysuckle commonly invades a woodland from the edge, slowly creeping in a little more each year. The shrub shades out all small trees trying to germinate in the understory leaving only the aged trees alive. Then come the vines, Japanese honeysuckle and wintercreeper, climbing the trees up into the canopy, overwhelming the upper branches. The tangle of invasive shrubs and vines can make a woodland impenetrable to the people who would like to care for it. Even if the shrubs are cut down, the vines persist on the forest floor, exploding with growth from the increased light available. Removing the shrubs and vines often causes erosion of the topsoil since there are no other plants to hold it in place. Garlic mustard joins the gang traveling in with flood waters and on boots, traveling deep into the heart of the forest. The mustard forms dense stands and spreads seeds that will last for years in the soil.
Once a woodland plant community has been displaced by these invasives its ability to regenerate is impaired. Topsoil is lost from erosion where the ground is not covered. The monoculture of non-native plants destroys the soil’s natural biome; the community of fungi, microbes, and insects that process nutrients. Seeds from the native plants have tried to germinate but the competition for resources was too fierce. The seed bank becomes entirely made up of the invader’s seeds to resprout year after year disrupting restoration efforts.
We are noticing these four horsemen invading our parks and yards. Early detection of the invasion is the best way to fight them. Woodlands will recover more quickly if they still have a wide variety of native plants to recolonize the area. Healthy soil with a rich microbiome can bounce back after restoration faster and fully. Help to save us from the apocalypse, don’t let the invasives get established.