Tom's Blog

Thursday, November 6, 2008

Oak leaves, the forest floor, and fire

In my post on the North Woods burn, I mentioned that oak leaves were ideal because they carry a fire well. The photo here shows a typical forest floor in an area of white oaks. The carpet of oak leaves is typical in areas that have not been burned. This is not from Pleasant Valley Conservancy, but in an old-growth forest that has probably not been burned for over 100 years. Under these conditions, decomposition more or less matches leaf fall, resulting in a fairly constant and substantial leaf pack. You can see how the oak leaves are curled up, which is partly why they carry a fire so well.

It is my opinion that most oak woodlands in southern Wisconsin should be burned frequently, no less often than once every three years. Burning top-kills invasive shrubs as well as small tree sprouts, keeping the understory open. Because of the shade, there is no summer or fall herbaceous flora. The only forbs are those that grow in early spring, before the leaves are out. Once leaf out has occurred, it is too shady for forbs, except in small open areas resulting from windthrow or disease.

On the other hand, if there are invasive shrubs on the ground, such as honeysuckle or buckthorn, the woods should not be burned until these woody plants have been dealt with first (probably by basal bark treatment with triclopyr or equivalent).

Note that this post is about burning oak woodlands. In my opinion, oak savannas should be burned annually, because the higher light regime greatly increases the chance for development of invasive shrubs.


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