Tom's Blog

Monday, November 29, 2010

Mazo Bluff buckthorn

This past Saturday morning, Kathie, Susan, and I joined Denny Connor's work party at Mazo Bluff. Denny has made great progress in opening up more of this nice prairie remnant, but there is still lots to do. The three of us were working down the side of the steep hill that faces east. The long-range goal is to get rid of all the trees and brush, at least on the upper part of this hill. Already, little bluestem is coming in where brush and trees had been cleared in previous years. But down the hill there was a forest of buckthorn!

Susan and I worked as a team. She used a lopper to cut the stems and I followed with the Garlon 4 bottle. Another volunteer, Justin, spent most of the time hauling our cut stems to a brush pile. While we were dragging our cut stems to the pile, the rest of the volunteers were on the other side of the bluff cutting pine trees, cutting them up, and throwing them down on our pile. Their goal there was to get rid of these invasive pines and open up the bluff so that visitors would get a view of the Wisconsin River valley to the west. (This is the bluff with the American flag and the star which is lighted every Christmas. It was lighted in a nice ceremony this past Sunday.)

What we were dealing with was a literal forest of buckthorn resprouts. The explanation for the resprouts was that a group of Scouts had worked in the area in years past, but were reluctant (or forbidden) to use herbicide. Yes, buckthorn does resprout when the cut stems are not treated. The cutting had been done quite a few years ago so that there has been plenty of time for new lengthy stems to develop. Take a look in Susan's photo below at the resprouts of these buckthorns. We counted as many as 25 stem resprouts from a single plant.

In addition to these previously cut plants, the steep hillside below was a dense tangle of buckthorns, all fairly large and substantial. I was interested in seeing all these large buckthorns because we no longer have anything like this at Pleasant Valley Conservancy. It took me back to those days in 1999-2000 when we were clearing our south-facing slope.

Not all prairie sites in our area have so much buckthorn. For instance, there is practically no buckthorn at Black Earth Rettenmund Prairie, and there wasn't much even before restoration work began. Why the difference?

An important factor in this Driftless Area is the nature of the bedrock. Buckthorn is a strong calciphile, and only flourishes in higher pH, calcium-rich soils. As it happens, the bedrock at Mazo Bluff consists of Prairie du Chien dolomite, whereas the bedrock at Black Earth Rettenmund is Tunnel City sandstone, except for a tiny bit of Black Earth dolomite atop the knoll.

For those who are interested in GIS, the reason I know the bedrock geology of these sites is that I have a shape file with all the Dane County bedrock formations, kindly sent to me by the Wisconsin Geological and Natural History Survey. I can overlay this file on top of the 2008 Dane County ortho-air photo, and the various formations (which are color-coded) line right up.

An interesting study would be a buckthorn survey of all the hills in western Dane County, since some are dolomite and others are sandstone. Nice graduate student thesis!


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