Sat July 25, 2009, 9:52 am

Drought Impact on Tree Growth and Survival

Last year NC experienced one of the worst droughts on record. Many landowners contacted us concerned with how the lack of water affected their trees. Lack of water reduces growth, lowers resistance to other stresses and will eventually lead to the death of the tree if the drought continues. Fortunately, trees have internal defense mechanisms to help them survive the effects of a drought.


As the amount of water available in the soil declines, trees react to minimize water loss and increase their chance of survival. They reduce transpiration by closing down the stomata (valve like openings) to reduce water loss. They will then increase fine root production to provide more root area to absorb water. Photosynthesis slows and the tree begins living on stored energy reserves. As the drought continues, biological activity further decreases. Roots stop growing, cell growth slows and new cell production ceases. Leaves shed prematurely, branches die back and roots die and shrink. All of these defense mechanisms are designed to protect the life of the tree.
 
Severe drought can affect the growth of the trees the following year. Food reserves may have been depleted during the previous year and roots may have died. The tree may need to replace these reserves and grow more roots to ensure survival, at the expense of adding new diameter or height growth. Signs of a severely weakened tree may be fewer and smaller leaves on the tree.
 
Widespread mortality is rarely seen in NC even in severe drought periods. In many locations, the recent drought has impacted the growth rate for this year, but the widespread loss of trees is not likely. Individual tree death has occurred, but it is most often associated with other stresses such as injury or poor root systems. Soil moisture in many areas of our state is not completely back to normal. Deep soils are still dry, even though recent rains have left the upper soils saturated. Assuming good rainfall this winter, soil moisture should return to normal by next spring. Increased soil moisture should also provide for a better growing season next year.
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