Construction Damage Kills Trees
Construction Damage is any injury that occurs to a tree during or because of any construction process including demolition, site preparation, or building.
Trunk and Canopy Damage
Trunk and canopy damage is evident and promptly noticed by the property owner. In some extreme cases, construction damage is severe enough trees may die almost immediately. Broken branches or scrapes/missing bark on the trunk are telltale signs of past construction activity (Figure 1). Usually trees will recover from these types of injuries if they are small, however, each wound allows microscopic decay organisms to enter the tree creating a potential for future problems. Construction equipment striking the tree and damaging the cambium layer on more than 50% of the tree can be a cause of rapid death.
Prune back broken branches to speed the recovery process and increase aesthetic appeal. Trunk wounds cannot be fixed once they occur, but they should not be painted with wound paint because this will actually cause more harm than good.
Construction damage most often occurs to the roots of trees and is hard to diagnose. Most damage goes unnoticed and causes slow decline over many years (5 to 10). Symptoms manifest slowly so property owners don’t draw the connection to the construction.
- A common misconception about roots is they are located deep in the ground, but 50% of tree roots occur within the first foot of soil.
- An astounding 90% of all tree roots are located in the top 3 feet of soil.
- Roots extend 2-3 times past the drip-line of the tree.
- More than 60% of the fine absorbing roots occur outside of the drip-line.
Let’s dig a little deeper into root damage.
Trenching and digging equipment will sever roots, as will lowering the soil grade. The closer to the tree roots are cut, the less likely a tree is to recover. Large roots cut inside a distance of approximately 4-5x the DBH (diameter of the tree at breast height) are structural roots. When multiple structural roots are cut, trees become unstable and unsafe. These trees should be considered for removal since the anchors have been cut (Figure 2). For example, if a tree measures 22 inches in diameter the structural root zone will be around 8-10 ft radius. Roots cut in the structural root zone greatly increase the likely hood of tree failure.
Impact of cutting Roots
- Expect recovery when less than 20% of the root zone is impacted on healthy trees.
- Cutting 20-40% of roots typically causes dieback.
- Cutting roots higher than 40% will usually cause tree death.
Recovery and survivability are dependent on the tree species and the condition of the tree before the damage occurred.
Fill and compaction suffocate tree roots.
Fill soil is material brought in to change or level grade after construction. This alters the soil respiration rate. Most tree roots are in the top 12 inches of soil because the gas exchange is better closer to the surface. Fill and grade changes limit gas exchange with the atmosphere and can suffocate roots. The structure and composition of fill can also change the hydrologic components of the soil (Figure 3).
Even temporary piles of soil can smother roots under the tree. Remove fill located around trees and return the soil to original grade to the drip line of the tree. (Figure 4)
Soil compaction happens when people, equipment, and supplies compress the pore space of soil (Figure 5). Healthy soil is roughly 50% pore space. Compacted soil dramatically reduce pore space reducing fine root development, and limit the amount of water available to the tree. Compaction also reduces the respiration rate of the soil. Reduced respiration causes stress on the tree, but the process is usually slow so damage will not show until years later. This is problematic because the time gap between construction and damage makes it hard for homeowners and contractors to draw a connection between the construction and the tree decline. Most contractors are unaware of the damage they cause.
Some soils compact more easily than others. Wet soils and soils with a high clay content are more susceptible to compaction.
Prevention is imperative
Prevention is the best way to keep trees healthy during and after construction. Wellnitz Tree Care can help you develop plans based on the tree species, age, condition, etc. to protect your tree from construction damage. We follow the American National Standard Institute guidelines (ANSI A300 part 5) to help establish tree protection zones and proper construction procedures around trees. Our practices help minimize damage and mitigate damage after the construction if encroachment occurs around tree protection zones. We work with contractors through the process from the planning phase through the post construction and landscaping.
Construction Damaged Trees
Wellnitz Tree Care helps trees previously impacted by construction activities as long as the damage is not too severe. Our certified arborists can alleviate soil compaction with an Air Spade or by vertical mulching. Products such as Cambistat can aid in fine root regeneration if roots have been severed. Unfortunately some trees we just can’t help. If this is the case we can remove the trees and grind stumps. Wellnitz Tree Care can even help you plant a new tree.