Invasive vines and shrubs are what is killing your woods

People worry about the wrong invaders. Insects and diseases get the headlines, but on most eastern woodlots the damage that can be prevented, and reversed, comes from plants. It is the work of a short list of vines and shrubs that arrived as ornamentals or wildlife plantings. They now change a forest more than anything short of a bulldozer.

Why vines and shrubs do the most harm

The vines climb. Oriental bittersweet, English ivy, Japanese honeysuckle, porcelain berry and the Asian wisterias, with kudzu across the South, all reach the canopy of a mature tree and shade its crown from above. A tree carrying a heavy load of ivy or bittersweet goes over in the first ice storm. A twining vine strangles a young tree as the trunk thickens against the spiral. A woodland edge left to bittersweet for twenty years is a line of dead and leaning trees under a green blanket.

The shrubs take the ground. Bush honeysuckles, autumn olive, multiflora rose, privet, burning bush and Japanese barberry leaf out weeks before native shrubs and hold their leaves weeks later. They form a layer at head height so dense that almost no light reaches the forest floor.

Tree seedlings do not survive under it. The canopy looks fine, but the forest has quietly stopped regenerating, and when those trees die there is nothing to replace them but more shrubs. The soil changes too: autumn olive fixes nitrogen and fertilizes ground that was never fertile. Barberry and honeysuckle litter breaks down fast and thins the layer that native seedlings and wildflowers depend on. Barberry thickets also shelter the mice and ticks that carry Lyme disease. Birds carry the seed to every fence line for a mile around.

Telling the fourteen apart

To get a name from a photo, try the tree identification tool.

Vines

Shrubs

Common and glossy buckthorn, brought from Europe as hedging, fill fence rows, roadsides and woodland edges with thickets that shade out native shrubs and stop tree seedlings. Common buckthorn holds its leaves in pairs or nearly so, and its twigs often end in a short thorn, while glossy buckthorn has no thorn and its leaf edges are smooth. The native Carolina buckthorn, alderleaf buckthorn and lanceleaf buckthorn carry finely toothed leaves singly along the twig, and a broken Carolina twig smells of almonds. Pull seedlings from moist soil, since a pulled seedling does not resprout. A cut stem does, so treat the stump at once, best from late summer through fall, then plant the gap from the refill list below.

“After buckthorn control, many sites will benefit from replanting of desirable tree, shrub, and herbaceous species. This will minimize bare ground which is often colonized by invasive species.” (Minnesota Department of Natural Resources, Buckthorn management)

The order of work

Start with what is killing trees, not with what is most visible from the road.

1. Free the canopy trees. Cut every vine climbing a tree in two places, at knee height and at shoulder height, and pull out the section between. A poison ivy vine takes the same cut, with gloves, as poison ivy and its look-alikes explains. Two cuts make the gap easy to see next year, keep the vine from bridging it, and leave a stump to treat. Do not pull the vine out of the crown; it will die and drop in pieces over a few years, and yanking it brings down branches and tears bark. Treat the rooted stump of every big bittersweet, wisteria or ivy, or it will come back from the roots.
2. Then the shrubs. Cut them at the base and treat the stumps, or pull them while small. Work outward from the best parts of the woods, where native seedlings are still coming up, rather than starting in the worst thicket; that protects more forest per hour.
3. Then the seedlings, every year. The seed bank and the birds overhead will keep supplying new plants for years. An hour or two each season pulling seedlings while small keeps the ground you cleared.

“Do not pull the cut vines from trees; this can further damage host plants and pose safety risks. The dead vines will shed their leaves, dry, and decompose over time, so the weight will no longer be an issue.” (Penn State Extension, Oriental Bittersweet)

Methods

Cut-stump treatment, in order:

1. Cut the stem low and flat.
2. Within a few minutes, dab the outer ring of the fresh cut, the living tissue just inside the bark, with a systemic herbicide labeled for cut-stump use. The plant carries it to the roots.
3. Work from late summer through fall into the dormant months, when the plant is moving sugars downward. Early spring, when sap is rising, is the worst season, because the flow pushes the treatment back out.
4. Follow the label exactly and keep the product off the bark of trees you are saving.
5. Check your state’s rules first, since applying herbicide near water or on land you do not own often requires a license.

Bush honeysuckle, privet, autumn olive, multiflora rose and bittersweet all resprout hard from an untreated stump, so cutting alone mostly makes more stems.

• Hand pulling. Seedlings and shrubs under an inch thick pull cleanly when the soil is moist, roots and all. Barberry and honeysuckle come out more easily than they look; multiflora rose fights back, so wear leather gloves. A lever-style pulling tool handles stems up to a couple of inches.
• Repeated cutting with no herbicide can wear a plant out: cutting the regrowth several times a season for several years exhausts the roots of honeysuckle, privet and bittersweet. It is real work, and most people give up before the plant does.
• Disturb the ground as little as you can. Bare, churned soil is a seedbed for the very plants you are removing. Pull small plants, cut and treat large ones rather than digging them out, tamp the soil back where you have pulled, leave the leaf litter alone, and keep machines off slopes and wet ground.

Whether you need a license turns on three things: the product, the place, and whose land it is.

“If you are considering using a restricted use herbicide, applying herbicides on property you don’t own, or applying herbicides in aquatic areas (such as a wetland or swamp), you may need a pesticide applicator license.” (University of Wisconsin–Madison Division of Extension, Managing Invasive Plants)

Patience

Count on several years of real work and then a lifetime of light maintenance. Seed of multiflora rose and honeysuckle stays viable in the soil for years, and birds keep bringing more. The first year looks like a wreck. The second year the natives you planted start to show. By the fourth or fifth year the woods look like woods again, with seedlings coming up on their own under a canopy no longer wearing vines. Take stock in late fall: bush honeysuckle holds its green leaves after everything native has dropped, so a November walk shows exactly what is left to do.

Refill the gap with natives

An opening cleared of honeysuckle refills with honeysuckle unless something else gets there first. Plant natives into the gap the same season or the next:

• Spicebush, for shaded stream banks.
• American hazelnut, for a sunny edge.
• Blackhaw, for a dry edge.
• Arrowwood viburnum and nannyberry, for fall fruit.
• Black elderberry, for the wettest spot.
• Witch hazel, for moist shade.
• Seedlings of the canopy trees.
• The natives above: put the seven on a request list and we reply with what is ready and current pricing.

The tree finder will match that list to the ground you have just cleared, and the Shade Understory Pack gathers understory natives for that gap in one order. Blue Whale Trees grows those understory shrubs from seed, so a dozen seedlings are a dozen different plants going into the gap instead of a dozen copies of one. Then protect them from deer; deer eat native seedlings and leave barberry and bush honeysuckle alone, one more way the invaders get their edge. Once a native canopy and shrub layer close over the ground, the sun-loving invaders lose most of their advantage and the woods start doing the work for you.

Common questions

How do I get rid of oriental bittersweet?

Cut every vine climbing a tree in two places, at knee height and at shoulder height, and treat the rooted stump within a few minutes of cutting, because bittersweet comes back hard from the roots.

Should I pull the dead vines out of the tree?

No: a cut vine dies and drops in pieces on its own over a few years, and pulling it down tears bark and brings branches with it.

Can I clear invasives without herbicide?

Yes, by cutting the regrowth several times a season for several years until the roots are exhausted, which works on honeysuckle, privet and bittersweet and takes more seasons than most people expect.

How do I get rid of bush honeysuckle?

Pull young plants from moist soil, roots and all, and cut larger ones low and treat the stump within minutes, best from late summer through fall. Cut and left untreated, it resprouts into more stems.