How to Assess Risk in Your Trees
Trees close to homes always carry some level of risk. Trees are large, living beings that can weigh several tons. If not taken care of properly, the risk present in trees can increase over time due to decreased health and structural weaknesses. Therefore, regular assessment of the risk your trees is part of proper tree care.
Having a Certified Arborist inspect your trees regularly is a good idea. However, there are several steps that you can take as a homeowner to assess your trees on your own. Performing such an assessment can help you decide when you need to seek out professional assistance.
There are five basic parts of the tree that you should examine to assess risk:
1. Trunk
When examining the trunk, you should be looking for wounds, especially those larger than a few inches in diameter. Cracks, especially horizontal ones, can indicate a structural weakness and impending failure. A cavity is a sign of structural weakness and of possibly internal decay.
A lean, especially a new lean, can be an indication of impending failure. While a tree can adapt to a lean over time, if a lean is new it can be an indication that the tree is starting to fail. Soil lifting often accompanies a new lean. Poor taper is signified by a stem that remains virtually the same diameter throughout the extent of the tree. Such taper can be indicative of a tree that is more prone to wind failure than others. Codominant stems and included bark are signs of structural weakness as well. They are indicative of a tree that may be more prone to splitting or large branch failure.
Cavities, such as the one at the base of this sycamore, can be a sign of internal decay.
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A leaning tree is not necessarily a problem, especially if the lean is not a new occurrence.
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2. Branches
The branches, or crown, of the tree can indicate tree health, while presenting a potential risk if large portions fail. Dead branches, especially those over an inch in diameter, can cause property damage or personal injury if they fail. However, a significant number of large branches can indicate poor tree health or internal decay.
An unbalanced crown and/or overextended branches can occur because of crowded growing conditions or genetics. If not corrected, such characteristics can lead to large branch failure. Codominant limbs are a sign of structural weakness, and can increase the likelihood of significant branch failure.
Cracks in branches, especially those over a few inches in diameter, can indicate imminent branch failure. Previous branch failures are indicated by broken or torn limbs or stubs in the crown. Such breaking points can be an entry point for organisms or decay, and can be an indication of future branch failures as well.
3. Leaves
Condition and appearance of the leaves can help determine the overall health of the tree. Health assessment is important, as healthy trees are better able to resist the spread of decay and other contributors to tree failure.
Leaves that are Chlorotic (yellowing or lighter green than normal) are indicative of a nutrient deficiency. This may be caused by a soil issue, or by an issue with the tree’s vascular system preventing the proper uptake of nutrients.
Browning of leaves often indicates a water issue, meaning that the tree is either not getting enough water from the soil or having difficulties moving the water to the leaves. Premature leaf drop can often signal a water issue as well.
Insect damage such as chewing of leaf edges, leafminers, and holes in leaves can indicate a stressed tree that is not as able to photosynthesize and produce its own food.
The branches, or crown, of the tree can indicate tree health, while presenting a potential risk if large portions fail. Dead branches, especially those over an inch in diameter, can cause property damage or personal injury if they fail. However, a significant number of large branches can indicate poor tree health or internal decay.
An unbalanced crown and/or overextended branches can occur because of crowded growing conditions or genetics. If not corrected, such characteristics can lead to large branch failure. Codominant limbs are a sign of structural weakness, and can increase the likelihood of significant branch failure.
Cracks in branches, especially those over a few inches in diameter, can indicate imminent branch failure. Previous branch failures are indicated by broken or torn limbs or stubs in the crown. Such breaking points can be an entry point for organisms or decay, and can be an indication of future branch failures as well.
3. Leaves
Condition and appearance of the leaves can help determine the overall health of the tree. Health assessment is important, as healthy trees are better able to resist the spread of decay and other contributors to tree failure.
Leaves that are Chlorotic (yellowing or lighter green than normal) are indicative of a nutrient deficiency. This may be caused by a soil issue, or by an issue with the tree’s vascular system preventing the proper uptake of nutrients.
Browning of leaves often indicates a water issue, meaning that the tree is either not getting enough water from the soil or having difficulties moving the water to the leaves. Premature leaf drop can often signal a water issue as well.
Insect damage such as chewing of leaf edges, leafminers, and holes in leaves can indicate a stressed tree that is not as able to photosynthesize and produce its own food.
Chlorosis can be an indication of a plant-soil mismatch. Source: umn.edu
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Insects, such as these hawthorn leafminers, can negatively impact tree health.
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4. Roots
Roots are a source of structural support and water/nutrient uptake for trees. Most roots occur in the top few inches of soil. Therefore, any activity close to the tree that affects the soil can have a significant impact on tree health and stability.
The root collar is the area where the tree’s trunk and roots merge. This area should be free of soil, mulch and other debris. A buried root collar can be an indication of a tree that was planted too deeply. Such a tree can suffer from many issues, such as stem decay and root suffocation.
Exposed roots, especially those with visible decay, can be a sign of poor root health. This may be an indication of a recent grade change or overland water flow, and may also be an indication that root decay is present below ground as well.
Root plate lifting and soil heaving can be an indication that the tree is beginning to fail. These signs are often present in combination with an increase in tree lean.
Soil saturation and weakness can increase the likelihood of tree failure through reduced friction and stability for roots to take hold. Soil saturation can be especially dangerous in windy areas.
Mushrooms present in the critical root zone can be an indication of root fungi. While many mushrooms do not indicate organisms that affect trees, fruiting bodies in the soil near trees are worth of further investigation.
Roots are a source of structural support and water/nutrient uptake for trees. Most roots occur in the top few inches of soil. Therefore, any activity close to the tree that affects the soil can have a significant impact on tree health and stability.
The root collar is the area where the tree’s trunk and roots merge. This area should be free of soil, mulch and other debris. A buried root collar can be an indication of a tree that was planted too deeply. Such a tree can suffer from many issues, such as stem decay and root suffocation.
Exposed roots, especially those with visible decay, can be a sign of poor root health. This may be an indication of a recent grade change or overland water flow, and may also be an indication that root decay is present below ground as well.
Root plate lifting and soil heaving can be an indication that the tree is beginning to fail. These signs are often present in combination with an increase in tree lean.
Soil saturation and weakness can increase the likelihood of tree failure through reduced friction and stability for roots to take hold. Soil saturation can be especially dangerous in windy areas.
Mushrooms present in the critical root zone can be an indication of root fungi. While many mushrooms do not indicate organisms that affect trees, fruiting bodies in the soil near trees are worth of further investigation.
Exposed roots with decay, can be an indication of a greater site problem.
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Saturated root zones, combined with construction activity, can lead to a slow decline in tree health.
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5. Surrounding Site
Conditions on the site surrounding a tree can greatly impact tree health and stability. Significant changes, such as construction and raising/lowering of grade can threaten the health and stability of trees. Many of the effects of site changes are not borne in trees until several years afterwards.
Construction activity, such as soil compaction and dumping of materials can degrade soil conditions for root growth. Compacted soils Even a few passes over tree roots by heavy equipment can cause irreparable harm. Storing of materials in root zones can cause chemicals from those materials to leach into the soil, where they are taken up by roots.
Root zone digging can sever roots, and any digging that takes place within the critical root zone could potentially have significant impacts on tree health and safety. Severe enough digging can compromise tree stability, and is cause for immediate tree removal. Grade changes, either lowering or raising the soil level, can cause significant root depth. Most tree roots are in the top few inches of soil. Raising the grade can cause suffocation of tree roots, while lowering grade can cause root severance.
Clearing of nearby trees can expose remaining trees to wind and light conditions for which they are nit adapted. Newly exposed trees may have small crowns, with vegetation only near the top of the tree.
Flooding and saturated soils can cause conditions not suitable for root survivability. While many trees are adapted to periodic flooding, if there is a sudden increase in intensity or duration any tree can be severely affected.
Significant issues with the trunk, roots and large branches can indicate a structural issue that means likely failure of a large portion of the tree. Issues with leaves and small branches likely indicate an overall health problem. While these issues may not signify imminent failure, they indicate that the tree may not be as able to prevent the spread of decay.
If you notice any issues such as those described above, please contact a Certified Arborist for further evaluation. An arborist can help develop a program to reduce or eliminate risk present in your trees to an acceptable level.
Conditions on the site surrounding a tree can greatly impact tree health and stability. Significant changes, such as construction and raising/lowering of grade can threaten the health and stability of trees. Many of the effects of site changes are not borne in trees until several years afterwards.
Construction activity, such as soil compaction and dumping of materials can degrade soil conditions for root growth. Compacted soils Even a few passes over tree roots by heavy equipment can cause irreparable harm. Storing of materials in root zones can cause chemicals from those materials to leach into the soil, where they are taken up by roots.
Root zone digging can sever roots, and any digging that takes place within the critical root zone could potentially have significant impacts on tree health and safety. Severe enough digging can compromise tree stability, and is cause for immediate tree removal. Grade changes, either lowering or raising the soil level, can cause significant root depth. Most tree roots are in the top few inches of soil. Raising the grade can cause suffocation of tree roots, while lowering grade can cause root severance.
Clearing of nearby trees can expose remaining trees to wind and light conditions for which they are nit adapted. Newly exposed trees may have small crowns, with vegetation only near the top of the tree.
Flooding and saturated soils can cause conditions not suitable for root survivability. While many trees are adapted to periodic flooding, if there is a sudden increase in intensity or duration any tree can be severely affected.
Significant issues with the trunk, roots and large branches can indicate a structural issue that means likely failure of a large portion of the tree. Issues with leaves and small branches likely indicate an overall health problem. While these issues may not signify imminent failure, they indicate that the tree may not be as able to prevent the spread of decay.
If you notice any issues such as those described above, please contact a Certified Arborist for further evaluation. An arborist can help develop a program to reduce or eliminate risk present in your trees to an acceptable level.