By Cody Gray
January 23, 2025
What is soil compaction and how can this affect the trees growing on your property? In this article we are going to cover the “do’s” and “don’ts” during the construction process to avoid soil compaction on the property. We’ll also be peeking into soil science as well as ways to regain healthy soil composition.
Soil compaction is caused when soil particles are pressed together, reducing pore space. Think of this like making a snowball - as you take a scoop of snow and press it together, it becomes hard and dense. The previously light and fluffy snow is now firm and sheds water. The same phenomenon is true with soil. As these particles are pressed together, air and water become scarce. With reduced pore space, water infiltration is much slower, and drainage becomes increasingly poor and insufficient. In addition to the soil’s inability to move and drain water, the exchange of gases is slowed down significantly. In poorly drained soils, the composition can turn hard and arid, causing a tree’s penetrating roots to struggle in seeking water.
Wooded lots offer extremely beautiful home sites. However, if approached improperly from start to finish, what could have been a serene place to kick your feet up at the end of a long day can slowly turn into a hazardous environment full of dead and declining trees. It’s no secret that heavy equipment is used to clear plots of land for both residential and commercial purposes. These pieces of equipment are often heavy and can cause substantial damage to the soil composition when extra care is not taken. However, there are ways to protect the trees you desire to keep if you are aware of some basic tree biology. In terms of spread, a tree’s roots mostly occupy the canopy drip line of a tree. The canopy drip line of a tree is the outermost circumference of the tree’s canopy in relation to the ground. A tree’s roots occupy this entire area and often extend two to four times the radius of the drip line. In terms of depth, most tree roots can be found in the first six to twenty-four inches of soil. This is important to know because this is where long-term root damage can occur if proper preventative measures are not taken.
When selecting the building site, it is important to choose an area as far away from the preserved trees as possible. However, at times this may not be possible due to the lot layout, construction needs, etc. There are ways to improve the likelihood of saving these trees inside of the construction zone. Setting up a tree protection zone can be accomplished by protecting the drip edge of the tree you plan to save. The idea is to minimize or prevent any travel of heavy equipment over this area to protect the tree’s valuable roots. One of the most effective ways to protect this precious area is by using T-posts, zip ties and a few rolls of orange barrier fence often referred to as a “snow fence”. The first step in this process is to walk out and mark the approximate drip edge of the tree. You can use orange marking paint on the ground if this helps. Next you will need to drive a T-post every four to five feet around the circumference of the drip line. Once you have traced the entire drip line of the tree, you will begin stringing your orange barrier fence and zip-tying it to your T-posts. This process is simple yet effective for keeping people as well as machines away from the root zone. Additionally, this will help limit the potential for damage to the trunk of the tree. If access is an issue and you are unable to successfully barricade the drip edge of the tree, another option is to use some sort of matting. This can be done with many different products. The simplest form of matting is plywood but whatever solution you use, this significantly reduces ground pressure, which reduces the effects of soil compaction.
Following the construction process, it is important to do a final walkthrough to determine if the grade has been changed. Any excess fill that may have been added inside of a tree’s canopy drip line should be minimized or avoided completely. A very small amount of fill used to fill in tiny divots or to lightly level the lawn is okay and unlikely to cause serious damage. A significant amount of excess fill or grade change can cause reduced oxygen and water infiltration for a tree's roots. A tell-tale sign is soil buildup around the root flare of the tree trunk. You can also take before-and-after photos and compare. If excess soil is present, it is important to remove it as soon as possible. The effects of soil compaction are not immediately noticed and often take months or years before it becomes apparent that something may be wrong. Unfortunately, by the time you notice that a tree is in decline, it is likely too late. Some key characteristics to look for include loss of leaves and premature leaf discoloration during the summer months as well as dead and decaying branches. It is not uncommon for one of our ISA Certified Arborists® to inspect a property containing a declining tree due to construction or renovation that occurred months or years in the past. Oftentimes this is discovered through a quick conversation with the property owner or when observing soil that is either compacted or covering a tree trunk’s root flare.
There are ways to improve soil composition following compaction if it is caught quickly. One of the most effective ways is by using an air-spade. An air spade is a tool that uses compressed air to loosen the soil around the tree’s roots. An arborist will push the tool into the ground around the tree’s root system and force air into the compressed soil, causing the pore space to increase. This is a non-invasive way to expose the roots to much needed water, oxygen, and nutrients. Another simple yet effective way to help with previous soil compaction is to mulch a tree. Removing 2 to 4 inches below ground level and backfilling with porous mulch can minimize the impact of soil compaction. There are also many benefits to mulching beyond just increased pore space.
In conclusion, remember to pick a building site that requires as little tree removal as possible. If there is a tree that is in question, it is much easier to remove the tree prior to construction and it will often cost less to do so. Complete a walkthrough with your contractors, express your concerns for the trees you plan on saving, and be certain to create your tree protection zone(s). This will take a little time in the beginning of the project but can end up saving thousands of dollars over the years to come. If you follow these steps and still end up with some soil compaction, don’t fret as there are still options. Reach out to your local arborists and inquire about air spading, tree mulch ring installations, frequent watering, or other plant healthcare options that might be recommended after an inspection. I can assure you that if you take the time in the early stages of the land clearing and construction process, the survival rate of your trees will increase significantly. If you are interested in a free tree quote by one of our 20+ ISA Certified Arborists®, call us at (614) 895-7000 or visit RussellTreeExperts.com/Quote
ADDITIONAL ARBOR ED ARTICLES!
Cody Gray I Senior Division Supervisor, Russell Tree Experts
Cody Gray is our Environmental Division Senior Division Supervisor and has been at RTE since 2016. He has worked around trees since 2013. He graduated from Hocking College with a major in forestry and is certified with aerial rescue, EHAT, first aid, CPR, and OSHA30. In his free time, Cody is an avid outdoorsman and enjoys spending time with his family. His favorite tree is the white oak because of their exceptional durability, beautiful grain patterns, and longevity.