Plant leaves manufacture sugar and carbohydrates that are the basic food or energy source for all plant processes – growth, root development and flower and seed production. Leaves also provide indirect benefits such as emitting oxygen, screening out air pollutants, shading the ground to moderate surface temperatures and intercepting precipitation to minimize erosion.
Defoliation, or loss of leaves, eliminates food production capability. This weakens the tree, reduces growth and results in pale leaves and branch dieback. Effects can range from a slight reduction in vigor to total death in severe cases.
When defoliation occurs early in the growing season just as leaves reach full expansion, it is most detrimental. At this time, considerable energy has been expended in leaf development but food reserves are not yet replenished. In spring, the tree is further weakened as it expends additional energy in refoliation.
Trees that receive regular care including pruning, fertilization, mulching and watering during dry periods are better able to tolerate defoliation. If a tree is defoliated, watering during dry periods is recommended to aid the refoliation process. Fertilization can also help encourage refoliation and replenish nutrients.