Denver Forestry
Drought Stress in Trees
Prolonged drought causes damage to the root systems of trees. The majority of the absorbing roots are in the top 12” of soil. These roots are very sensitive to drying out, and are the first part of the root system to be affected. When the absorbing roots die, the leaves cannot get enough water to function. In addition to the direct root damage, water stress affects the number of leaves in the buds set for the following season.
Symptoms of water stress will not generally show up until the damage has been done. Some damage may not show up until one or two years later. Symptoms include: wilting, yellowing of leaves, leaf scorch-brown and dry areas, premature leaf drop, cracking of the bark on young trees, twig and branch dieback in more severe cases. Needles on evergreen trees will brown from the tip inward. They will also shed more needles in fall than in years with sufficient moisture. Under prolonged drought conditions, trees will show a general thinning of the canopy, and twig and branch dieback. Called defensive dieback, it is the effort of the tree to compensate for root loss.