Tom's Blog

Monday, January 5, 2015

Lack of significant buckthorn invasion at Black Earth Rettenmund Prairie

Buckthorn (Rhamnus catharticus) is a calciphile and proliferates primarily in areas where the soil is rich in calcium and magnesium. In the Driftless Area of Wisconsin, soil calcium is derived mainly from underlying dolomitic/limestone bedrock. At Pleasant Valley Conservancy we have some areas with underlying dolomite and other areas with underlying sandstone. Buckthorn infestations are only found in significant amounts in the dolomitic areas. Several years ago I gave a Poster on this at the Prairie Enthusiasts meeting.

At Black Earth Rettenmund Prairie buckthorn is only found in a couple of small areas, and I was interested to see the distribution here in relation to bedrock. A few years ago geologists at the Wisconsin Geological and Natural History Survey sent me a GIS-adaptable file of the bedrock geology of Dane County. I used this in ArcMap to plot the distribution of dolomitic rocks. The map here shows the results.

Bedrock underlying Rettenmund Prairie. Only two small areas of
Black Earth Dolomite are present; all other areas are underlain with sandstone

There is a thin band (about 20 feet thick) of Black Earth dolomite that is present in two small areas of the prairie and this is where the buckthorn was found. There was no significant buckthorn in either of the sandstone areas.

The principal dolomitic rock in Dane County is the Prairie du Chien dolomite, but this is at a higher elevation and is not present at Rettenmund. However, at higher elevations, such as Pleasant Valley Conservancy or Mazomanie Bluff, this is the principal bedrock, and buckthorn is a major problem in those areas.

I haven't had time to look at other parts of Dane County, but with the bedrock-GIS file, this should be easy to do. Note that this analysis can only be done in the Driftless Area, where soil is derived primarily from bedrock. In glaciated areas of Dane County, soil calcium/magnesium will depend on the nature of the glacial deposits.


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