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Moment of Nature - Aug. 23, 2013

Root damage: a slow killer

Posted: August 22, 2013 1:53 p.m.
Updated: August 23, 2013 5:00 a.m.

“Out of sight, out of mind” applies very well to the root systems of trees. The parts of a tree within the upper portions of soil are vital to tree health, but hidden from the human eye. The causes of root damage are many, the effects are significant and treatment options are limited.

Symptoms of root damage include a gradual dieback on the outer extremities of the crown, small and discolored foliage or sudden death during extremely hot weather. A slow death, with gradual dieback in the crown, is the most common symptom of root damage. Trees do not always show symptoms above ground, however. Sometimes, the only clue that there’s a problem is the sudden uprooting of the tree. This can occur during storm events of rain, wind, ice. Less common, are tree failures on a calm day. Needless to say, a large tree falling without warning can result in property damage, injury or death.

Contrary to popular belief, most trees (at least in this part of the world) have very shallow root systems. Roots are opportunistic, and grow wherever they have space, water, oxygen and nutrients. The level of oxygen in the soil is the primary factor (of the four listed) which restricts root growth to the top few inches of soil. Feeder or fibrous roots need oxygen for respiration and growth; the farther down in the soil profile, the less oxygen occurs. Where deep, rich, porous soils exist and drainage is good, some roots may be a foot or so deep, but such conditions are rare in our state. The roots of most trees extend far beyond the “drip line” or canopy edge to as much as three times the height of the tree.

Unfortunately, it’s easy to do serious damage to a tree’s roots. Activities such as grading during site preparation for building construction or even slight grading removes the fibrous roots and has a detrimental impact on the tree in the years to follow. In addition, soil compaction from vehicle traffic, material storage or foot traffic not only crushes roots, it also reduces pore space in the soil, discouraging the re-growth of roots. Excavation, trenching and even roto-tilling for landscape purposes can do enormous damage to root systems. Installation of irrigation systems is a common tree killer, due to root damage. A less obvious killer of roots is a change in drainage. Drying out a site can dry out and kill roots. Conversely, over-watering or saturated soil conditions, much like what we’ve got going on now, can drown roots and kill them. Some trees, like dogwoods, don’t like “wet feet” and are more susceptible to insect pests. In the past few weeks, at least four dogwoods along our street rights-of-way have died as a result of the soil conditions. Lastly, “fill dirt” gives the same effect as drowning. The roots are deprived of oxygen and cannot vent carbon dioxide from respiration, so they die. Even a few inches of soil fill on top of a tree’s root system is enough to kill large trees.

Depending on the extent of damage to the root system and the size and condition of the tree, death may result after a long and slow decline over the course of many years to a decade. Root damage deprives the leaves of water, a basic raw ingredient used in photosynthesis (the food-making process for green plants); it disrupts growth by removing growth regulators manufactured in the roots; it removes stored food; and it creates wounds, causing the tree to reallocate resources for defense. Wounds on damaged roots provide opportunities for harmful fungi (root rots) to enter. A tree with damaged roots may become unstable and subject to strong winds or may even fall over of its own weight on a calm day.

Root rots are caused by fungi, most of which enter a root system through wounds. Wounded roots occur in nature, but root damage caused by human activity is generally on a large scale and is accompanied by other factors that stress trees and make them less able to cope with a fungus infection. Root rot fungi are present everywhere in the soil, but need a root wound and a weakened tree to be harmful. The most commonly found root rots in South Carolina are inonotus, armillaria, ganoderma and phytophthora in hardwoods; and leptographium, annosum and polyporus in softwoods. Even though this may be all Greek to you, the bottom line is these root rots are serious and sneaky – sometimes taking decades to degrade and under-mind a tree’s root system.

When trees suffer serious root damage, treatment options are limited. Trees can regenerate lost roots, but only if a satisfactory environment for root growth exists. A well-aerated soil with a good layer of composted mulch will encourage root growth and such conditions can often be provided for smaller trees. The extensive root systems of large trees make soil amelioration difficult on a scale large enough to be of much benefit. Since the immediate need of a root-damaged tree is water, irrigation can be of great help. Be careful though, over-watering can create boggy soil conditions and encourage phytophthora root rots, so the watering schedule should allow for the soil to dry out between applications. Soil aeration can also be very beneficial for root regeneration. Fertilization of root-damaged trees is not recommended, since fertilizer will increase a tree’s need for water and cause it to reallocate resources needed to fight off disease and grow new roots.

“An ounce of prevention is better than a pound of cure” applies well to the problem of tree root damage. Where soil disturbance is to occur near trees, it is best to identify the critical root zone (CRZ) and then protect that area from any soil disturbance or compaction. The CRZ is easiest to establish by means of a radius of at least 1 foot per inch of tree diameter. For example, a tree 10 inches in diameter (measured 4-1/2 feet above the ground) would have a CRZ in a 10-foot radius around the tree. This area should be fenced with a sturdy fence, identified with signs and zealously protected from any activity until construction is completed.

Root protection is simple in concept, but difficult in execution. The basic principle is, stay far away from the trees! The difficult part is convincing others that the mere act of walking, parking, storing materials, grading, filling, trenching or digging may do irreparable harm to a tree’s roots and result in its slow death from disease or starvation. Healthy root systems are vital for healthy trees.

If you have any questions regarding an upcoming construction project or home landscape improvement that will impact the soil and a nearby tree, please feel free to contact me (before the project begins!) at the Camden Public Works Department (425-6045).

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