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What is Buckthorn?

The Buckthorn Menace: The only tree without a reflection

by Myles Bakke, Manager of the Cowling Arboretum

In the past sixteen years, since my position as Arboretum Manager was created, I have spent most of my time dealing with the control of invasive exotic species on our land. The list is extensive and grows longer as new threats appear on the horizon every year. Buckthorn is the most visible of the exotics to invade the Arb woodlands, but is not the only one that we spend time controlling. Honeysuckles, Siberian elm and garlic mustard are all problems in our forests, at least in certain locations and to various degrees.

It is widely believed that buckthorn was introduced as a landscape ornamental and hedgerow planting from Eurasian origins early the twentieth century. I would not however, discount the rumor that it arrived here as seed in soil layers covering the floors of a shipment of caskets from Transylvania.

There were, I’m sure, a number of buckthorn established in locations along fence lines and field edges throughout the Arboretum as early as the nineteen fifties, spread to those sites by birds. In the mid-nineteen sixties, when the college stopped ranging cattle on hillside pastures along the Cannon Valley and other locations in the Arb, buckthorn exploded in those disturbed areas unchecked and for the most part unnoticed. It is a small tree, usually no more than twenty feet in height, but is a nearly perfect invader that crowd out under story plants almost completely. By 1991, when I began to cut these trees, I found some with trunks over a foot in diameter. We began by killing these older trees to get rid of the seed source, but within two weeks found a ground cover of thousands of new seedlings sprouting from the seed bank in the soil. With the canopy removed and sunlight hitting the soil again, we increased our population by multiple orders of magnitude. Eradication was clearly not a one step operation. We pulled and poisoned, cursed and excoriated it, but did not eradicate it. I began to think of buckthorn as the floral equivalent of the antichrist. Our methods now are a bit more heavy handed, but far more effective. In areas flat enough to use equipment on, we uproot the cut stumps and seedlings, and disrupt the soil with a special grubbing blade on a Bobcat skid loader. We still have to knock the dirt from the roots since the tree will continue to grow and reestablish itself even lying on its side. The shallow root system, that allows for easy removal, is the only positive aspect of this pernicious exotic.

Buckthorn, like other evils, is here to stay. At present there is no known biological control, so we need to rely on angry villagers brandishing shovels and axes if we are going to affect any measure of restraint on this menace in our neighborhoods and our wild places. The Buckthorn Menace Art Project is a great step toward raising public awareness and involvement, and I’m excited to have the Carleton Arboretum included as a site for the installations.