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Farm and Forest The Effects of Drought

The Effects of Drought 

The forest continues to show stress from our continuing drought. Some areas have fallen at least 24 inches below normal rainfall over the past three years. As the water table drops, the sub-surface soil on which trees depend has been drying up. Especially in upland areas, trees have had a harder and harder time getting enough water in between rains. Over time, the stresses build. 

The tree to the left shows "epicormic branching." Branches sprout down the trunk, trying to make up for leaves lost at the top. 

Upland Red Oaks and Black Oaks, both members of the Red Oak family, are showing the worst effects. The drought weakens them and makes them more vulnerable to pests. Armillaria Root Rot, a fungus, can attack their roots. The Two-lined Chestnut Borer attacks the crowns and stems.

The fungus in the roots prevents them from taking up enough water and food. Damage done by the borer makes it hard to transport nutrients to the leaves and stems. Oaks, particularly middle-sized ones, begin to die. This means that the forest is losing a generation of red and black oaks that will never grow to become good timber. 

Another insect pest is the Red Oak Borer. It tunnels deep into the wood without directly killing the trees. This insect normally lives in the forest, but its numbers are increasing as it takes advantage of the stressed trees. The tunnels left by the borers lower the value of the wood.

Oak Decline 

Tree death is common after drought, and the death of oaks is a natural process. From time to time trees die from competition with other trees or from old age. Bare branches high in a tree's crown are signs that this is happening in red and black oaks. White oaks and post oaks are long-lived trees with high tolerance to drought, so they are not declining as much.

Ozark woodlands were often more open in pre-settlement times, with more pine than there is now. The black and scarlet oaks grew in thickly after natives stopped using fire to clear the underbrush, logging, and the deep rooting of free ranging hogs (the pioneers' favorite livestock.) We can look at the decline of red and black oaks as a return to the pre-settlement balance of a more open white oak and pine forest.

Wondering about your own woods? 

If you see a tree declining here and there, it's natural and no big deal. You may want to keep an eye on your trees, and think about cutting declining trees for firewood. If there are many, a timber sale may be in order. A forest naturally changes. Old trees eventually die, while young trees replace them. This is why it's nice to have mixed age stands, with room for some young trees to grow into the forest. Carefully managing a forest over the long term allows landowners to benefit both "naturally" and financially.

Sources: David Haenke, independent forest manager; Hank Dorst, Ozarks Forest Watchers.
The Broadcaster, Fall 2001; Missouri Forest Products Association News, May 2001.