Tom's Blog

Friday, April 11, 2014

Burn-induced mortality of a mature bur oak

Bur oaks are very resistant to damage by fire. However, they do age and the trunks do get hollow, opening them up to fire damage.

In our savanna burn of last Sunday, one of our largest oaks (Tree #720 in our database; located in Unit 10), caught fire internally. Although alive, this 21.8 inches diameter oak had a large hollow trunk. In addition, there was a large knot about 8 feet from the bottom, also hollow, and this hollow connected to the main trunk. During the savanna burn, wind must have swept sparks into this open knot and started a fire, which spread into the middle of the tree. The upper part of the tree was leaning and its weight, as the trunk was weakened by the fire, pulled the whole tree over. (See photos)

Tree 720 down the day after the savanna burn

Close-up of the trunk and bole of tree 720

Just before the burn in Unit 10. Tree #720 is nearby. The fuel here is predominantly Indian grass.

After the burn. Parts of Tree 720 can be seen at the right.
Although this was the largest oak that fell as a result of the burn, there were about 10 other smaller oaks that came down.

Although the loss of large oaks is sad, it is inevitable in a fire-controlled savanna. In fact, this is one of the ways the canopy stays open. And if the canopy were not open, warm season grasses such as Indian grass could not flourish.

The oak savanna of Pleasant Valley Conservancy is not a backyard garden, where every tree is protected, but a natural landscape!


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