Water deficit develops as a normal phenomenon in plants when water loss by transpiration exceeds the rate of absorption from soil. Chronic injury results from long-term exposure to low water supplies (e.g. in areas with poor soils) and is expressed by growth loss and increased susceptibility to parasitic fungi and insects. Acute injury occurs under extreme water deficiency and is expressed by significant growth loss or death. Symptoms of drought damage include wilting, discoloration of foliage and premature leaf fall. Progression within the crown is from the top down and outside in, and the roots are usually the last portions to die. Symptoms can be similar to those of trees suffering from root disease, except that with root diseases, the roots die before the foliage. In the Southwest, drought symptoms have been observed in many trees including aspen, ponderosa pine, piñon, and soapberry.

Winter drought is particularly harmful in Southwestern upland forests and can render large areas vulnerable to bark beetles and wildfire.

References:  83, 93

Figure 282. Western soapberry with branch dieback following dry spring.

Figure 283. Aspen branch dieback during summer drought.