Tom's Blog

Wednesday, August 10, 2011

Anatomy and significance of a buckthorn root collar

My interest in buckthorn growth and survival continues. Eventually this knowledge should lead to better understanding of how to eradicate this exceedingly undesirable plant.

At Pleasant Valley Conservancy I have been following buckthorn growth in one small test area for the past dozen years. The big plants were cut and treated or basal barked (both with Garlon) in 1999-2000. The area has been burned annually ever since.

Buckthorn shoots have continued to arise each year. Where are these shoots coming from? The seed bank had been long exhausted. Were they shoots that had been missed in previous years, or were they new growth from underground stems or roots?

To attempt to get a handle on this problem, last year I very carefully killed every visible buckthorn shoot in this test area. I made sure there were no visible buckthorn plants by returning every few weeks to kill any new shoots that might have arisen. At the end of the growing season in October, I did a final canvas to make sure there were no living buckthorn plants visible.

At the end of July this year I did another survey of this same area. Imagine my surprise to discover 71 small buckthorn plants! Where are they coming from? I dug one of these plants and carefully cleaned all the soil off. The photos below show the result.

Despite the fact that this was a fairly small shoot, it was attached to a surprisingly large root mass. The root itself, and the root collar, was thick and woody. Further, arising from the root collar were thirteen shoots, each of which must have been part of some previous year's growth. Remember, the site has been burned each spring.

My interpretation is that this and the 70 other plants I found, have arisen from dormant root masses, which remained lurking underground waiting for favorable growth conditions.

It looks to me that without some heroic measures, eradication of buckthorn seems pretty unlikely. Areas cleared of buckthorn must be followed up in future years, and new shoots treated with herbicide. This must continue until all the underground dormant root masses are gone.

This situation is not unique to Pleasant Valley Conservancy. I have seen a number of sites in Dane County where large buckthorns were removed a few years ago and not followed up. These sites are now full of buckthorn regrowth. (I'd be happy to send anyone interested a list of these depressing sites.)

Fortunately, not all sites at Pleasant Valley Conservancy have such a large storehouse of dormant root masses. Many of our sites are now in fairly good shape, although almost every such site has to be canvassed in early summer for small buckthorn plants that need to be herbicided.


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