What Is Soil Compaction?
By Sherrie Ottinger (The Tennessee Dirtgirl)
Image © Andreusk | Dreamstime.com
What is soil compaction and why does it matter? Have you ever taken a shovel and tried to dig in a gravel driveway, or barn lot, or even in a heavily trafficked yard? Here in east Tennessee, you’ll often be hard pressed to get down more than a couple inches. Yes, we have clay, and clay is dense, but that’s not always the problem.
When I owned/operated a landscape service in Knoxville, compaction was a big problem, especially with new construction. The land would have been purchased for the way it laid, its expansive views, maybe its remoteness. The homeowner would dutifully heed counsel and set up perimeters around old growth trees that they wanted to preserve, but they didn’t often consult an arborist before deciding where to sit these perimeters.
As time, and construction passed, the activities around the property included big trucks, digging machinery, passenger vehicles being parked and driven across the areas over and over. There would be a change in the plans; add a bigger patio, a sidewalk, expand the footprint of the house. Often this brought activities very close to the boundaries of the old trees, yet it didn’t seem to affect them, so on it went.
I would usually be called 5 years or so, after all this activity, because the old oak, hickory, sweet gum, or maple had been “acting poorly” the last couple years, and this year it appears to be dead. These folks were sure they’d done everything right to protect the trees.
We’d walk the perimeters where boundaries had been set and the compacted areas were obvious to me. Many times, this compaction was well under the canopy of the tree. Trying to dig shovel full of soil, told the story. The sides of the tree that hadn’t been affected, were often still clinging to life. Compaction of the soil on the roots of the trees, was the cause of death. The homeowner could’ve saved money and frustration by having the old trees cut before construction, if they weren’t going to get a true tree person involved. They might have been able to have them lumbered, and sold or made into furniture or part of the new home. The expense of cutting massive trees, close to a building, is also massive, due to liability.
What had gone wrong in the protection phase? Most homeowners mean well when they try to save those beautiful majestic trees, but they don’t understand the whole picture. A tree’s roots reach at least as far as the canopy (the farthest out limbs), and in old trees, it can be double that…or more. The feeder roots are fibrous and form a webbing, of sorts, that only go into the first foot of soil. In an ideal setting, the roots are healthy because the soil is not compacted, so water and oxygen can move in and out with minimal effort. The soil-life that the tree depends on for exchange of nutrients are healthy. When compaction occurs (remember large equipment, digging equipment, passenger vehicles, etc.?) the delicate web is destroyed. Soil spaces are smashed closed. Oxygen and water and nutrients can no longer flow freely, and the tree suffocates, or drowns, or starves to death.
Some trees are more tolerant of adverse situations, and some absolutely do not want soil disturbance. Oaks are very intolerant. So, why did they not die in the first few years? The death blow can be dealt to a mature tree, as long as ten years before it completely dies. Something as simple as talking with a TRUE arborist would’ve saved this loss, because the homeowner would’ve gotten an education on the fact that trees are much like people; they have their preferences and intolerances. Plants need the same things you and I do – oxygen, water, food, space.
Compaction occurs in many places in modern life. I’ll talk more about it next week.
The Tennessee Dirtgirl
