Abiotic disorders in trees.

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" Abiotic disorders affect the normal growth and development of a tree. They may disrupt water and mineral uptake or other vital functions, which sometimes causes a domino effect of physiological dysfunction within the tree.

Many agents of abiotic disorders are primary stress factors that can become the first stage in a spiral of decline. Each successive stress that follows contributes to this decline, which can further reduce the possibility of reversing the trend.

Signs of abiotic disorders may be difficult to recognize. Learning the history of the site and of the tree often provides the biggest clues. Knowing about temperature or moisture extremes in recent years, for example, can help. Unfortunately for the diagnostician, it can take a long time for the tree to react to the primary stress factors. Because of this, the link between cause and effect is often lost.

A common mistake in diagnosis is to carefully examine the trunk and crown of the tree while overlooking the root condition. Root-related problems are often difficult to diagnose due to their limited accessibility. Symptoms observed in the upper portions of a tree often result from poor root health.

If a transplanted tree declines or dies within the first year, the most likely cause is either a lack or an excess of water—which may be related to planting depth, soil compaction, or poor species selection. If the tree’s root ball is too small or if a saturated condition restricts new root formation or water absorption, the tree will suffer from the lack of water and reduced nutrient uptake. 

Every species of tree has optimal levels of light, water, soil conditions, and growing space. Trees that are planted in sites that do not provide adequate levels will be stressed. Poor tree and site matches are the basis of many tree disorders.

Another common site problem is soil compaction. Without sufficient pore space, water and oxygen will be limited. Root growth and water absorption will decrease, causing the tree to decline or die. Beneficial biological activity in the soil can also be inhibited by the lack of water and oxygen.

Soil samples and tissue analyses can help determine whether a mineral deficiency is present. A soil analysis will give the pH as well as the levels of many of the essential mineral elements in the soil. Certain mineral toxicities, such as aluminum, are associated with low-pH soils. Changing the soil pH, however, is not always practical.

Decay near the place where the root system and trunk join, the trunk flare, or in the structural roots can be a serious flaw that can lead to tree failure. 

Some indicators of decay in the roots or trunk flare include dieback, abnormal leaf color, fungal fruiting bodies, and uneven form. Excavating soil near the base of the trunk to expose buttress roots can help an arborist locate decay.

To properly diagnose a problem, it is important to understand the difference between physical injuries and physiological disorders. Physical or mechanical injuries, such as lightning, lawn mower damage, and vandalism, occur suddenly, while physiological disorders develop over a long period of time. 

Often, the full extent of damage due to physical injuries cannot be immediately assessed. In some cases, initial treatment should be limited until the extent of tree damage can be determined. For example, with lightning injury, it may be a year or more before the effects of electrical current passing through a tree’s tissues are exhibited. The same is true for construction damage.

Lawn mowers and string trimmers can damage trees by wounding or girdling the lower trunk and sometimes damaging surface roots, which may cause decline or even death. Trees suffering from mechanical injury may have less than ideal structural support. Mechanical injuries may take years (if ever) to become apparent in the crown.

Trees in urban areas can be damaged by cars, bicycles, pets, or vandalism. Trees with thick bark are more tolerant to damage than trees with smooth, thin bark.

Sometimes the causes of physical damage can be eliminated to prevent injury to the tree. For example, where lawn mower injury is a problem, the area around the tree should have the turfgrass removed and replaced with mulch. 

It is always preferable to prevent physical damage than to treat a tree after the event, because treatment options are typically very limited. Broken or damaged branches can sometimes be removed, but it is up to the tree to compartmentalize the pruning wounds.

Extremes in temperature, either high or low, and other weather-related problems can be damaging or even lethal to trees. Weather-related problems include moisture extremes, snow, ice or wind damage, lightning, hail, and the use of de-icing salts.

Low temperature injury can affect all plants and all parts of the plant, although injury to the roots is not as common unless the tree is in a raised planter with insufficient soil volume. Species type and time of year have a large effect on the extent of damage caused by low temperatures. 

Some species are able to withstand temperatures far below freezing, while others may be killed at much warmer temperatures. Also, plants that have not been given a chance to become acclimated or have not been hardened off are more likely to experience freezing and chilling injury.

Freezing injury occurs when temperatures drop below the freezing point. When a temperature is below the freezing point, ice crystals can form inside plant tissues, which may potentially rupture cell membranes. This often leads to dehydration and death of the tissue. Injury that occurs from low temperatures that are above the freezing point is referred to as chilling injury. Chilling injury often affects the integrity of cell membranes, causing leakiness.

Trunks and stems can develop frost cracks when temperatures drop rapidly. This temperature drop causes the outer wood and bark of the tree to cool rapidly, shrinking and cracking. Frost cracks can also form when moisture in the inner wood freezes and expands, splitting the bark. Once a tree has been damaged in this way, it will frequently be re-injured in the same place in subsequent years. Callus growth in vertical lines along the trunk is a symptom of frost cracks. 

Similar to frost cracks is sunscald, which typically occurs on the south or southwest side of trunks or branches and is due to rapid change in temperature resulting from solar heating. Thin-barked trees or trees with bark that has been suddenly exposed to sunlight (due to removal of shade) or previously injured trees are more susceptible to sunscald. Young trees are also more susceptible to sunscald.

Trees are often broken from the heavy load of snow or ice. Ice can add thousands of pounds of weight to the branches of a tree. Ice damage can be particularly devastating, as it often damages almost all of the trees in an area. Tree failures can lead to loss of life, power outages, and millions of dollars in economic losses.

High temperatures can also place stress on trees, especially when combined with drought. In urban settings, reflected heat from pavement and buildings can add to the heat load on the plant and lead to wilting, leaf scorch, sunburn, and tissue death. Plants with limited soil volume or in raised planters are especially susceptible to high temperature stress. 

Wind can break branches, tear foliage, destroy flowers, or cause tree failure. The increase in transpiration due to high winds can also cause a plant to lose excessive water, resulting in drought symptoms and leaf burn, especially if the soil water content is not high enough to compensate for the increased water demands.

Storm damage can be classified in several ways. Blow-over is when trees are physically pushed over by high winds, and stem failure is when stems fail, often at wounds or cavities. Crown twist is another example in which stem twisting magnifies weaknesses around old injuries and, during a storm, the stem may split or branches may collapse.  Root failure entails roots being pulled or snapped, causing trees to fall or lean. Branch failure happens during ice storms or downbursts where branches become susceptible to tearing downward along the stem or snapping off. 

Lightning strikes can cause serious damage or even kill a tree. A sign of lightning strike is a spiral scar running down the length of the trunk. The scar follows the grain of the wood where the bark or sapwood has exploded off the trunk. The full extent of internal damage may not be obvious. There can be structural weaknesses in the wood, and, if the cambium is killed, the tree may not leaf out the following spring. 

Hail causes immediate damage to the leaves, bark, and branches of a tree. Symptoms usually include torn or tattered leaves and broken, bruised, or scarred branches. Thicker leaves may show pitting on the upper surface. Severe hail may completely kill the bark on one side of a stem and lead to devastating defoliation of the tree. 

Salts can also damage trees by increasing the osmotic potential of the soil. This change draws water out of the roots, creating drought symptoms in the plant. Excess salts can also create metal toxicities and deficiencies by blocking certain mineral uptake channels in the roots.

Trees can decline as a result of competition with other trees and plants. Competing for sunlight is the most common form of competition between trees. Shade-intolerant trees growing under the canopy of larger trees may exhibit death of lower branches, stem curvature, and reduced growth.

Trees may also compete with turf and other plantings for available soil nutrients, water, and growing space. Tall fescue and other grasses can stunt the growth of young trees when grown over a tree’s root system.

Allelopathy is the chemical inhibition of growth and development of one plant by another. Many trees and other plants produce chemical substances that affect the growth of other plants. Allelopathic chemicals may be exuded directly from the plant or released indirectly through decomposition. These chemicals may inhibit growth, seed germination, flowering, or fruiting of nearby plants. In most cases, the inhibition is minor and not easily diagnosed. 

A few trees are considered highly allelopathic, including walnuts (Juglans), sugar maple (Acer saccharum), and black locust (Robinia pseudoacacia). Young trees and stressed plants are more susceptible to allelopathic effects than nonstressed plants or plants with large, established root systems.

Pollution (air, water, and soil) damage to trees may be divided into two categories: acute and chronic. Acute toxicity results from exposure to high concentrations of toxic compounds over a relatively short period of time. 

Chronic injury is due to long exposures, usually in much lower concentrations. Other factors that affect pollution damage are type of pollutant, species tolerance, wind, temperature, humidity, soil grade and type, precipitation levels, and the general condition of the tree.

Pollution damage is often difficult to diagnose unless the source of the pollutant is known. The symptoms may mimic other problems such as insect injury and mineral deficiencies. Most of the symptoms of pollution damage will be evident on the foliage.

Dieback or necrotic areas may appear on the leaf tips, along the margins, or between the veins. The leaves may appear whitish or silvery. There may be some stippling or spots on the leaf surface.

Although any number of chemicals can kill or injure a tree, herbicides are the most frequent culprits. Because herbicides are formulated to kill plants, they contain phytotoxins. The growth regulator herbicides, such as 2,4-D and dicamba (used to kill broadleaf weeds in the lawn), may harm nontarget broadleaf plants such as trees and shrubs. 

These materials are systemic, which means they move throughout the plant. Exposure may be a result of drift, accidental spraying, root grafting, or movement into the soil.

If a tree has been exposed to systemic herbicides, the leaves will often begin to curl and cup, and the shoot tips may become twisted. New foliage will show varying degrees of parallel venation. The foliage may appear wilted and become chlorotic before dying and falling off. Other symptoms include veinal or interveinal chlorosis, marginal chlorosis, and leaf fall. Exposure to other herbicides may cause trees to exhibit similar symptoms. Herbicide-damaged plants may recover unless exposure is severe.

Certain herbicides (nonselective herbicides or soil sterilants) have greater potential to cause serious damage than most growth-regulator herbicides, and caution should be used whenever these are used near trees or landscape plants. 

When applying any chemicals, the instructions and precautions on the label must be carefully followed. To minimize the chance of accidental herbicide injury, never use the same spray equipment to apply herbicides and to apply fungicides or insecticides. Spray only on cool, calm days to avoid drift. Using low pressure increases droplet size and reduces drift. Apply the herbicide to target plants only, and always check the product label for possible phytotoxicity to the surrounding plants. Always use great caution when applying herbicides within the root zone of trees. If they must be used within the root zone, be sure the product is labeled for such use.

When applying herbicides in turfgrass, guard against potential drift to trees and shrubs. Avoid spraying desirable plants. Sometimes, plant damage to adjacent properties can occur from crop treatments. Most of the time, the damage is not severe, and the affected plants recover. Be sure to disallow any herbicide applications under the drip line of any tree or shrub. " (information cited from ISA study material)

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