Moisture stress on trees affects every physiological process adversely. The first response is the closure of the leaf stomata. This acts as a defense mechanism by reducing the transpiration of water. With the stomata closed, the curtailing of photosynthesis is the result, as carbon dioxide is not absorbed. The stoma is a pore, tiny leaf opening, found in the leaf and stem epidermis (many on each leaf) that is used for gaseous exchange. This reduction in photosynthesis limits the growth and production of carbohydrates (energy) which increases the trees susceptibility to insect pests and disease.
Water stress inhibits the production and translocation of essential materials in the plant, (listed below) and further contributes to the reduced growth and development.
- · Carbohydrate (food) production
- · Proteins
- · Enzymes
- · Growth regulators
- · Mineral nutrients
This restricted growth and energy are evident by stunted chlorotic leaves, premature defoliation, crown thinning and poor shoot growth. Trees typically require several years to recover fully from drought. As trees grow, they expend energy in creating a root system that will support them in times when water is scarce. The fine root hairs, multiple-branching, non-woody roots constitute the major proportion of the surface of the root system. Their primary function is to absorb water and minerals. Non-woody roots and root hairs are the first parts of the root system that are affected by drought. When these roots become nonfunctional or lost, a water deficit develops in the plant because these roots can no longer provide sufficient water to the top of the plant.
Soil is a complex web. When soil dehydrates, the beneficial organisms drop off in population levels and yet the evil opportunistic organisms remain. Drought stressed trees are more vulnerable to disease and pests. Common pests on drought stressed trees include borers, bark beetles, and canker as well as root disease and fungi. The invasion of these pests and disease may ultimately cause death of the tree.
What can be done to help reduce the affects of drought stress on your trees?
- · Irrigate: water your trees at least 1 inch per week. Use a rain gauge to know how much to water.
- · Mulch: mulch conserves soil moisture and adds organic matter to the soil, promoting root development. Preferably, add mulch to the drip line of the tree with a depth of no greater than 4 inches and at least 2 inches from the trunk of the tree.
- · Fertilization: only a Certified Arborist should determine the specific type of fertilization needed by your tree (s). There are so many factors, which should be considered, such as soil condition, i.e. sandy or clay, and moisture content.
- · Pest Management: Drought stressed trees are particularly prone to pest infestations. Pests should be managed once detected with the appropriate treatments through biological or chemical means.
Contact your Wachtel Tree Science Certified Arborist for questions or concerns regarding drought stress and your trees.