Among the many threats to eastern forests is Buckthorn. In many ways Buckthorn is the most insidious of threats. It does not kill Oak trees the way Oak wilt does. It does not out-compete the Oaks for sunlight like Black Cherry or Box Elder might. Instead, it stops the reproductive cycle while eliminating other less obvious native species such as sedge and woodland wildflowers, often replacing them with pure stands of Buckthorn.
Buckthorn is comprised of two species in southern Wisconsin, glossy and common. Glossy Buckthorn typically grows in wetter areas and common grows almost everywhere else. Both species were introduced from Europe as landscape shrubs. In Europe, they tend to be fairly inconspicuous. In this country however, they have some distinct advantages over the native species with which they compete. Along with invasive honeysuckle, they are the first plants to leaf out in the spring. Ordinarily, Oaks leaf out in early May giving the spring wildflowers ample time to grow, bloom and set seed. When Buckthorn takes over, these plants are quickly shaded out.
Buckthorn also seems to have an allelopathic effect. Studies have shown that germination of native species is significantly reduced when Buckthorn leaf litter is present, suggesting a chemical in the leaves is the cause. As Buckthorn begins to dominate, many other species disappear. As it takes over, native shrubs and young trees will be affected. Eventually, regeneration of Oaks and Hickories will be greatly disrupted. As the mature Oaks die, there will be no young Oaks to succeed them and eventually the woodland will revert to a brush wasteland dominated by Buckthorn, Honeysuckle and a few straggling Elms, Box Elder, and Cherry.
Wildlife such as deer and song birds typically do not use a Buckthorn-dominated woods for various reasons. While a Buckthorn thicket may look dense and healthy to us, to a coyote it looks like an umbrella. Under the canopy is bare soil. Deer make very little use of Buckthorn for food as it is generally unpalatable. Only a few species of bird are known to nest in Buckthorn.
Luckily, several techniques have been developed in the restoration industry to push back the invasion of Buckthorn. The first step is to remove or kill it. This can be done in several ways. Hand removal with a root wrench is the most labor intensive, but has the benefit of not requiring herbicide application. It can be cut with a chain saw, piled and burned. After cutting, an appropriate herbicide, usually containing Triclopyr, can be applied to the stump. This also is very labor intensive, but very effective especially in less dense infestations where workers can move around more easily. It is also possible to kill Buckthorn where it stands by applying herbicide to the bark. This however, has the obvious disadvantages that come with having possibly hundreds of small trees to deal with.
The most effective method for larger scale and fairly dense infestations (greater than 1 acre or so) is to use a forestry mower. These machines quickly cut and shred Buckthorn leaving only wood chips and sticks behind. After the Buckthorn re-sprouts it can be sprayed with a Triclopyr-based herbicide. This will result in a very dramatic and quick reduction of Buckthorn density. It may also be necessary to remove other trees and shrubs, including native trees such as Black Cherry, Box Elder, Ash and Elm if too much shade still remains.
Once the Buckthorn is removed it is critical that native ground cover vegetation be restored. Otherwise, Buckthorn and many other weeds will quickly re-colonize. In some cases, native ground covers may be present and may come back on their own. In other cases, installation of native woodland grass and sedge seed is the quickest route. If broadcast in the fall, germination is usually pretty reliable in the spring. But the following spring, you may have enough fuel to conduct a prescribed burn.
Fire is an essential tool for maintenance of all woodlands, savannas, and prairies in southern Wisconsin. For thousands of years our native ecosystems developed adaptations to fire. Without occasional prescribed burning, these native plants cannot thrive. Buckthorn seedlings will not tolerate fire. And once native ground covers become established, keeping Buckthorn at bay is relatively easy.
After a few years of burning and killing any Buckthorn that survived initial efforts, native wildflowers can be introduced. The end result can be quite stunning in its beauty, diversity, and habitat value.
Methods and Estimated Costs for Buckthorn Removal
Hand Cutting: $1,500 - 3,000 per acre
Stump Herbicide: $150 - $250 per acre
Burning Piles: $500 – 2,000 per acre
Forestry Mowing: $350 – 500 per acre plus a mobilization charge
Herbicide Re-sprouts: $150 - 250 per acre
Seeding: $300 – 600 per acre
Prescribed Burning: $1,500 for a typical 20 acre site