Tom's Blog

Thursday, September 25, 2008

Hazelnut as an invasive shrub

We have always had a fair bit of hazelnut (Corylus americana; also called American filbert) in our savannas and have felt this is a "good" species to keep. The fall color, for instance, is outstanding. It is often mentioned in the surveyor's notes in the Public Land Survey for southern Wisconsin, so presumably they considered it a good plant also. It forms edible nuts, although at Pleasant Valley Conservancy the squirrels usually get them before we do.

However, in a recent survey of one of our nice white oak savannas, I noted that hazelnut has spread quite a bit. I am starting to worry about whether it might "take over" the savanna.

This savanna has a lot of good species, including cream gentian, culver's root, various savanna and prairie grasses, lion's foot, purple Joe Pye, purple and yellow hyssop, asters, and goldenrods. But since hazelnut forms an extensive rhizome system, it is forming large patches which are beginning to crowd out these good plants. Although hazelnut is fire sensitive, it readily resprouts after fire. Also, in several of our savanna areas, the hazelnut cover is extensive enough so that fire doesn't burn through. In a few years, I am afraid this shrub might be towering over my head.

In our savanna areas we have had an ongoing brush control operation, focusing on exotics such as honeysuckle and buckthorn. But we have been leaving the hazelnut. Now I am starting to worry about whether we might have allowed it to go too far.

Research at Cedar Creek Natural Area in Minnesota has shown that hazelnut can dominate the understory in oak savannas. For instance: "Our results suggest that fire-dependent ecosystems may be more vulnerable to shrub expansion, due to the resprout capabilities of shrubs after single disturbances and high light availability. We recommend monthly clip treatments during the growing season to effectively manage C. americana expansion, either with or without prescribed burning." Brian D. Pelc, Peter B. Reich, and Rebecca A. Montgomery. Universityh of Minnesota.

I'm not sure we would go as far as monthly clip treatments. I would rather contain its spread from some of the savanna areas by killing the spreading edges of the clones, enough so that they were held back.


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