Hi, I’m Debbie Smith, Chief of Historic Landscapes Program at NCPTT.
Today I’m going to discuss ways to protect your trees before a storm and how to recover after a disaster. Storm effects that I’ll be covering include: Flooding, lightning strikes, and primarily wind damage.
To prepare for a disaster, you need to know your trees and how to protect your resources. And by “resources,” I mean not only features that would be adversely affected by falling limbs or trees, but also the trees themselves. The first thing you should do is inventory to identify both significant and hazardous trees. Trees can be designated significant in a number of ways…They may be historically significant to a town or to a property, their size can be considered significant, such as a large tree that is listed or eligible for state or national recognition as a Champion, or a mature tree that adds beauty to a site and may provide important shade.
A tree may also be culturally significant, such as this oak tree that was a Native American meeting place in Bureau County, Illinois. A tree might also be personally significant as a favorite tree. Unfortunately, no matter how significant a tree is, it may also be a hazard. How do you know if you have a hazardous tree? To be a hazard, a tree needs to have a significant structural defect and there needs to be a target, something that a falling tree can potentially hit. Hazardous trees are among the most likely trees to be damaged or destroyed during a storm and to cause damage to other features.
As depicted in the image on the left, there are two targets…the person and the building. And although the tree on the right has major structural defects, it’s not considered hazardous because there’s not a target. To determine if something is a potential target, you need to define the target zone. The zone should include 360 degrees circumference around the tree and a radius that equals the height of the tree plus 10%. So for a 50-foot tree, the target zone should extend 55 feet from the trunk in all directions.
When assessing potential targets related to a hazardous tree, you need to be aware of both stationary targets, such as the building, fence, plantings, pathway and picnic table depicted in this image, and also moving targets such as the children in this image. The potential for moving targets is greatest in high-use areas where people typically gather such as backyards, parks, picnic areas and playgrounds.
As part of your inventory, check your trees for visible obvious structural defects. Types of structural defects that may create a hazardous condition include weak branch unions and cracks, a tree with a deep crack, or a crack that extends completely through the trunk as depicted in the tree on the right is likely to fail.
Cankers are sinking or missing bark… The presence of a canker increases the chance of breakage near the canker. Trees with decayed wood are prone to failure. The seriousness of the decay is based on the ratio of the healthy wood to the decayed wood. And dead trees and large dead limbs in the proximity of a target should be removed immediately.
Trees especially prone to blow over in a storm are those with roots confined in small spaces or with roots that have been severed as there is not a healthy spread of roots to anchor the tree. But keep in mind, a tree with a serious defect is not a hazard unless it’s within striking distance of a target.
Before a disaster, consult a certified arborist to professionally evaluate your trees for potential hazards. An arborist can also perform preventative pruning to remove deadwood and broken and hanging branches, to correct structural defects, and to reduce the canopy mass to allow more wind movement through the crown during a storm. Cabling and bracing may also be installed to add structural strength to individual limbs or to an entire tree.
Despite preventative measures, some trees will remain hazardous. If this is the case, you will need to decide if the value of the tree is as significant or more significant than any potential targets. If the tree does not have significant value or if the value of the target is greater, the tree should be removed.
For some significant trees, such as this 800-year-old oak in Scotland, extreme measures may be taken to protect both the tree and potential targets. One way is to restrict access around the tree such as the fence in this image. Other possibilities are to reroute pedestrian traffic away from the hazardous tree or to move a target such as a bench or a picnic table. For all trees that you want to preserve, identified as hazardous or not, there are things you can do to protect their structure and health, making them better prepared to withstand a storm.
One thing to consider is the installation of lightning protection. Although an expensive procedure, it may be appropriate for highly significant trees, such as the tulip poplar depicted in the image on the left that was planted by George Washington at Mount Vernon. If you look close, you can see the copper cable running down the side of the tree, which is then grounded within the tree’s roots. Visible to the tree on the right is damage caused by a lightning strike. While some trees can withstand a lightning strike, for others it’s fatal. Lightning damage may be more harmful to the tree than its outward appearance indicates as damage can extend down into the roots.
During a construction project, tree roots need to be protected against soil compaction, as most roots are located in the upper 6 to 12 inches of soil. The area around the tree canopy should be fenced off to prohibit truck traffic, parking and the storage of materials under the canopy. This is an example of what not to do. The tree depicted in the image will be a major asset to the park under construction, yet little thought to its welfare was considered during the construction project.
In some cases, construction may need to occur within the tree canopy. This is often the case during installation of underground utilities or sprinkler systems. The best practice is to work as far away from the tree trunk as possible and to tunnel between the roots instead of trenching through them. Trenching close to the trunk as depicted in this image severs major roots that lead to smaller feeder roots needed to draw water from the soil. Here is the same tree one month after construction, and then four months later. Trenching so close to the trunk hastened its death.
For particularly significant trees, you might consider taking cuttings to grow a replacement tree so that following a disaster you can replant with the same genetic stock. After the storm, recovering includes both immediate concerns and long-term concerns. And there may also be ways to receive financial recovery through compensation for lost trees. The most immediate concern is personal safety. Trees that are unsafe or trees that have become hazardous should be addressed first. Never attempt to remove a tree or tree limbs that have fallen on power lines. To assess tree damage, ask yourself the following questions:
Is the tree basically healthy other than the storm damage?
Is the leader branch, or the vertical branch at the top of the trunk, still intact?
Did major branches survive the storm?
Is at least 50% of the crown or the canopy still intact?
And, are there remaining branches that can form new branch structure?
If you answer “yes” to a majority of these questions, there’s a good chance the tree will survive. Uprooted trees are often unnecessarily removed. Young trees, generally 10 inches in diameter or less, and planted within seven years, can sometimes be saved. Straighten these as soon as possible and the trees will often recover. Support the newly reset trees with stakes for about a year so they can reestablish a strong root system. Freestanding larger trees should not be attempted without the advice or assistance of a certified arborist.
Tension caused by the roots remaining in the ground can cause the tree to snap back. Removal of trees in archaeologically sensitive areas should be done in consultation with an archaeologist so that resources embedded in the root mass are either preserved or properly removed. One method is to cut the trunk several feet from the base and reset the root mass back into the ground leaving any archaeological artifacts embedded in the root mass. Another option is to hand excavate, water flush, or air spade the root mass to inspect for artifacts before removing the tree from the site, then backfilling the root pit after applying a layer of clean sand into the opening. The sand provides a layer of differentiation between the undisturbed soil and the soil examined for artifacts.
For severely damaged trees, dramatic pruning may be necessary to retain the tree. This is best undertaken by a certified arborist. To prevent damage to adjacent resources during tree work, use resource protection methods such as the plywood A-frames covering the headstones depicted in this image. Mechanical injuries associated with debris carried in floodwaters or by wind may put the health and structural integrity of a tree in jeopardy. While these injuries may not at first appear serious, they may pose structural and health issues for the tree over time.
Trees that sustain prolonged periods under floodwater are susceptible to a number of long-term problems, including a loss of soil around the root system caused by rushing waters, decreased oxygen available to the root system, and changes in the soil pH. Trees associated with flooding should be monitored for up to two years for flood-related symptoms. These symptoms include limb dieback, wood decay and wood rot, increased insect damage and disease. A final consideration is financial recovery. Check to see if your property insurance covers the loss of trees in addition to any structural damage caused by fallen trees.
One insurance recovery method is based on the value of the tree before the storm. This is calculated on its size, species, pre-storm condition and location. A tree’s significance is not included in this equation. A second method is based on the cost and clean up and repair of the tree. In some cases you may be able to take an itemized deduction on your personal Federal Income Tax for trees lost during a storm. Basically, the deduction is calculated by figuring the loss in property value after the storm and subtracting any insurance payments received plus $100 plus 10% of your adjusted gross income. Keep in mind, even if a building is not damaged, a major loss of trees might account for a significant loss in property value.
To conclude, it’s important to remember that trees can be both a landscape asset and also a liability.
Keeping both of these points in mind is necessary when preparing for and responding to major storms.