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: a short list of vines and shrubs that arrived as ornamentals or wildlife plantings and 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, hold their leaves weeks later, and 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, and barberry thickets shelter the mice and ticks that carry Lyme disease. Birds carry the seed to every fence line for a mile around.

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. 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.

Methods

• Cut-stump treatment. Cut the stem low and flat, and 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. The best season runs 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, because the flow pushes the treatment back out. Follow the label exactly, keep the product off the bark of trees you are saving, and check your state’s rules, 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.

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, American hazelnut, blackhaw and the other viburnums, elderberry, witch-hazel, and seedlings of whatever trees make up the canopy. 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.

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.