Tom's Blog

Thursday, May 20, 2010

Bur oak resprouts after fire

The upper part of our south-facing slope is a fine savanna with some nice large bur oak trees that are completely fire tolerant. They produce acorns, of course, which tumble down into the prairie remnant below. Some of the acorns germinate and make seedlings which are top-killed by our controlled burns. However, an important characteristic of oaks is the ability to resprout after fire.

What happens to these resprouts? They are killed again by the next fire, etc. etc. Will they ever turn into large trees? Eventually, one or more of these small seedlings may escape fire. If that happens a few years in a row, they may get large enough so that they become fire resistant. Bur oaks are noted for their thick, corky, fire-resistant bark.

Yesterday, I surveyed the south slope for resprouts of "bad" plants that needed spraying (brambles, buckthorn, honyesuckle, sumac, etc.). I was fascinated by the large number of bur oaks that were resprouting. The photo here shows an example. You can discern the corky bark even on these small plants.

An interesting thing about these resprouts is that the leaves lack the characteristic bur oak shape. They have rounded lobes, putting them clearly in the White Oak subfamily, but lack the deep indentations that are generally seen on leaves of larger bur oaks.

How old are these plants? We have been burning this part of the south slope for at least 10 years, which gives an upper limit for their age.

Although fire is keeping the stems of these oaks from reaching any significant size, the root system is another matter. Oaks are noted for their extensive root systems. Instead of starting over each year, as the stems have to, the roots can continue to grow and enlarge. Bur oaks in particular have very impressive underground root systems. (In 1932 the distinguished Nebraskan prairie research John Weaver excavated the root system from a small bur oak grove and published photographs of the underground network. His paper can be found in the Botanical Gazette, Vol. 94, pp. 51-85.)


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