Trees add beauty and value to a property, and paving over their roots can put them at risk. A tree's roots provide it with all of the nutrients and water the plant needs to survive, as well as air, so burying them in concrete or tar will impair the tree's health substantially, or even kill it. Several options give you a chance to both save your tree and put in a beautiful driveway.
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Most of the root system the tree needs to survive is located along the drip line, an area directly below the branches of the tree. Protecting the drip line area is the first step in maintaining a healthy tree while paving. According to the University of Minnesota, 90 to 95 percent of a tree's root system exists in the top three feet of soil with more than half in the top one foot, making excavation in preparation for paving detrimental to the tree's health.
Problems and Consequences
Once pavement is installed over a tree's roots, the tree loses some of its ability to get water and air, since most pavement is nonporous and will seal the roots away from the aeration and rainfall the tree needs. In addition, the tree roots are liable to push up the pavement as they grow, resulting in damage to driveway. The roots may also cause a tripping hazard as they push through the pavement. Once the tree becomes less healthy, it may blow over in a windstorm, or the tree may simply die from its inability to get water and air.
Avoiding the Roots
The University of Minnesota says that a paved driveway may cover up to half of the distance from the drip line to its trunk without significantly harming the tree. Better yet, if space allows, consider redesigning the route of your driveway so the paving project stays away from the tree's roots altogether. You may want to put a bend in the driveway to avoid paving over the roots. If you can get by just cutting one or two roots, neatly cutting them with a hand saw helps them heal properly. Cutting multiple roots of the tree is not an option, since the health of the tree will likely decline and the tree may become structurally unstable.
Pavers offer a beautiful option in place of concrete or tar paving since they do not show cracks from roots invading the pavement. Pavers allow water and nutrients to reach the roots. If the roots continue to grow, it's easy to lift the pavers and regrade the area. Another option includes the use of permeable paving, also known as permeable concrete. Permeable paving offers an effective way to allow water and air to seep into the ground around the roots of your tree. Another advantage to permeable paving includes its ability to collect rainwater while reducing stormwater runoff and erosion.