Stresses in trees may be caused by natural factors and conditions or through the activities of man or animals. These factors may be chronic (recurring and lasting for a long time) or acute (immediate impact). Examples of chronic damage are wet soils caused by site selection, soil compaction or poor nutrition. Acute damage includes flooding, freezing conditions, severe construction damage and deer browsing.
Tree stresses may be very dramatic and obvious or not easily observed or recognized. Obvious stresses may include basal damage or storm damage. Stresses from grade changes, soil compaction or pollution are not very visible.
Trees often do not display immediate responses to stresses because of their accumulated growth habit. However, with stresses come several changes within the tree depending on the damage caused by the stress. In some cases, the process of photosynthesis, which is the primary supply of carbohydrates for all tree functions, is reduced and the tree’s stored food reserves are depleted.
When root systems are damaged by construction damage, compaction or poor drainage, they cannot supply adequate water and nutrients for the trees growth and survival. When this happens, often the tree is unable to produce sufficient carbohydrates and growth regulating chemicals.
When trunks or stems are damaged, the carbohydrates movement to where it is needed for growth and function is stopped, and may result in death of roots or other growing points of the tree. The end result of these reduced processes is that the tree, at best, operates at less than peak efficiency and in many cases it begins a downward spiral of all of its growth functions.
As stresses continue, the tree does eventually exhibit external symptoms. Annual incremental growth is reduced and becomes significantly less than normal. Leaves may be fewer in number and smaller in size. Sometimes, the tree produces excess fruit or seed as a survival mechanism. The tree may exhibit summer scorch symptoms because of insufficient water provided to the leaves during dry weather.
With continued stresses, branches begin to die, and at the same time the root system of the tree is reduced because the crown is producing inadequate food for good root expansion and growth. These processed continue into a downward spiral, usually resulting in the continued decline and eventual death of the tree over a period of 2-15 years. In most cases, once the tree has tipped the balance of not providing sufficient carbohydrates for continued growth of the tree, it cannot recover.
If the physical stresses do not kill the tree, it often will be exposed to more stresses through opportunistic diseases and insect attacks. These biotic attacks may speed up and/or complete the demise of the tree.
Much of the survival, growth and health of our woody vegetation in our landscapes is dependent on the homeowner working to prevent stress and provide the optimal growing environment for the tree. This may begin with plant selection to ensure that the selected plant will perform well on the specific site and soil.