01. What is a certified Arborist?
02. Why hire an Arborist?
03. Do my trees need pruning?
04. What trees should I plant?
05. Why is topping a tree bad?
06. How will drought affect my trees?
07. Do I need to water my tree in the winter?
08. Do my trees need fertilizing?
09. What are humic acids?
10. What are Mychorizae?
How will the drought affect my trees?
Drought causes primary and secondary physical damage as well as physiological changes in trees. The primary physical effect of drought or dry soil conditions is direct damage to the roots and root death. Nonwoody feeder roots, usually located in the top 18 inches of soil, are particularly sensitive and are the first ones affected. Effects of drought are particularly severe on seedlings or new transplants due to root loss during the transplant process. For example, balled and burlapped trees are estimated to contain only 5-20% of their original root mass after digging. For container-grown trees, the medium in which the transplant is growing can be a major factor—many of the soilless mixes used for container stock are highly porous, dry out very quickly, and are very difficult to re-wet. This situation creates moisture stress in the rootball regardless of the availability of water in the surrounding soil. The problem often continues until the roots grow beyond the rootball. Contrary to popular opinion, it often takes woody transplants two years to become completely established in a new site. The rule of thumb: for each inch of tree caliper, one year of recovery from transplant shock is necessary. As a consequence, these trees should be given extra care and attention during extended periods of drought.
Established trees and shrubs are also affected by drought, especially those planted in marginal sites such as those with pavement over their roots, those in pockets of soil on ledges or in sandy soils, or those that have been improperly planted. Drought can exacerbate even the most subtle improper planting practices! Native plants are usually adapted to regional and seasonal fluctuations in the amounts of available water. Therefore, only unusually severe drought is likely to injure plants that are growing naturally in a given site. However, most of the trees that we deal with are landscape trees with poor mechanisms for adaptation to drought stress.
SYMPTOMS of drought:
Symptoms of drought are manifest in many different ways depending on the tree species and the severity of the water deficit. However, it is generally agreed that symptoms are often not evident until sometime after the event has occurred—even as much as one to two years later! Unfortunately, symptoms of drought stress are usually subtle, not specific, and not diagnostic. This makes accurate diagnosis very difficult. Symptoms are quite variable and include loss of turgor in needles and leaves, drooping, wilting, curling, yellowing, premature leaf or needle drop, bark splitting, and tip and branch dieback. Leaves on deciduous trees often develop a marginal scorch and interveinal necrosis whereas needles on evergreens turn brown at the tips or appear off-colored. Trees can also exhibit general thinning of the canopy, poor growth, and stunting. Many woody species exhibit symptoms of general "decline." In extended cases, drought can result in tree death.