Coping with construction is the most challenging obstacle many trees will face in their lives. Given enough time to adapt, trees are extraordinary organisms that can withstand many environmental stresses; however, the rapid environmental changes wrought by construction occur too quickly for many trees to survive.
While some trees’ health may decline within days of construction-related stress, others seem to take the damage in stride.
Unfortunately, this is not always an accurate reflection of such a tree’s health, and many of these stoic specimens die a few years after construction takes place.
The only way to prevent large-scale tree losses during construction is by understanding the biology of trees and the types of stress that construction projects create. With adequate foresight and planning, many of these loses can be prevented. Additionally, by understanding which trees are unlikely to survive a given project, you can focus your conservation efforts where they are most effective.
Soil Compaction, Grade Changes and Root Health
A sample of soil is comprised of minerals, organic matter, innumerable microscopic organisms and small voids, called pores by botanists, geologists and others interested in such matters. Some of these pores hold water, while other pores contain air. These pores are very important for trees.
While the large roots flaring out from the trunks of trees anchor them to the ground, they do not absorb significant amounts of water or air. Trees leave this job to their many fine roots, located further from the trunk.
The problem occurs when construction activities compact the soil. This destroys the pores in the soil, preventing the trees from absorbing water and air. Additionally, if compacted enough, the tree’s roots can become trapped and unable to grow in a normal manner.
Many different construction activities compact the soil, such as preparing the foundation of the building, or simply the heavy vehicle traffic associated with construction projects. Even if efforts to prevent compacting the soil are taken, grade changes can just as easily doom trees.
The fine absorbing roots of trees primarily reside in the upper 12 inches of the soil. They penetrate this type of soil well, and are able to provide the tree with resources from a relatively wide area. However, when additional soil is placed over tree roots, it reduces their ability to survive. Grade lowering efforts often sever roots, which is as traumatic and destructive as it sounds.
Mechanical Trauma and Bark Damage
Perhaps the simplest and most obvious form of damage trees suffer from construction projects is mechanical damage to the trunk or major limbs.
Whether heavy equipment snaps part of a tree’s lower limbs, or laborers using hand tools rip large portions of bark from a tree’s trunk, the tree’s primary defense mechanism – the bark – is compromised, opening the tree up to a variety of pests and pathogens. If the cambium layer is affected, the wounds may be serious enough to kill the tree.
Some trees are more resilient than others are in the face of such indignities. Those trees with thick bark are better able to recover from damage to the trunk or major limbs than those with thin bark are.
With adequate tree protection zones in place, such damage is less likely to occur.
Trees that grow in the open often develop broad crowns and root systems that help them to withstand strong winds. Over time, many of these trees even produce wood in places that improves their ability to withstand the prevailing winds. However, trees that grow in forests — or where competition limits the spread of their canopy and roots — are more susceptible to windthrow.
Living inside the forest, this is rarely a problem, as the nearby trees partially block the wind. However, when trees along the edge of the forest are removed, it exposes the trees behind them.
These newly exposed trees are now at increased risk of failing, perpetuating the pattern of exposure and failure. In addition to increasing their susceptibility to blowing over, these formerly shaded trees may develop sunscald.
When considering any construction project that will take place near trees, you should secure the services of a skilled arborist to assess your trees and develop a tree protection plan. In many jurisdictions, such a plan is required before construction begins.
The arborist will help devise tree protection zones, consider the potential effects grade changes and predict how the trees will respond to changes in wind and water flow. Your arborist may also investigate the health of your existing trees to determine which measures – if any – are appropriate. For instance, trees may require supplemental watering or fertilization, prior to the onset of construction.
Dead branches should be pruned for safety’s sake, and structural pruning may be required to ensure the tree has the greatest chances of surviving the construction. Mulching is usually a good standard practice, but during construction activities, exceptionally thick mulch layers may be warranted.