Drought

Water is a critical component of nearly every physiological process in plants; without water, trees will rapidly wilt and die. On average, trees require 1 inch of water per week. A large mature oak can lose nearly 400 gallons of water on a hot summer day through transpiration. Fortunately, trees have vast root systems that, using mychorrizal associations, can access water from the small spaces between soil particles. Trees respond to short term water shortages by closing small pores in the leaf surface called stomata and minimizing transpirational water loss. Longer periods of drought can cause wilting and browning of foliage, embolisms in the tree’s vascular system which further inhibit water translocation, dieback of the tree’s crown, and eventually death. Drought symptoms will first appear where water is lost at the highest rates (foliage) and at points farthest from the water supply (leaf tips, inter-veinal leaf tissue, and the upper crown). It may take a tree several years to fully recover from prolonged drought. Drought stress can make trees highly susceptible to secondary stress agents.