We don’t often think about the roots of trees until there is a problem.
A forester friend of mine called it a “fencepost mentality.” Being underground, roots are often out of sight, out of mind. However, without well-functioning roots, tree health begins to decline.
When asked to draw a picture of tree roots, many folks often draw something that looks like a carrot, with a taproot and small, branching roots coming off the taproot.
The root system of a tree looks more like the base of a wine glass, with roots growing horizontally. As a tree’s canopy grows, the roots grow along to supply the leaves with enough water and nutrients to thrive.
When we see a decline in the tree canopy, it is usually a clue that something is going on with the root system.
Root damage due to construction activities is one of the largest contributors to tree decline. In many cases, fill material is placed over the root systems. This reduces the amount of oxygen getting to the tree’s roots. As roots are starved for oxygen, they die or become targets for disease.
Construction can sometimes mean cutting roots. Arborists generally warn against cutting any root within five times the diameter of the tree trunk.
Soil compaction also can reduce root health. In healthy soil, 50% of the soil volume is filled by water and air. This allows roots to absorb water and breathe. If the soil is compacted, there is less room for air and water.
Vehicles parking on soil, heavy lawn mowers traveling on the same path and foot traffic can compact soil enough to inhibit root growth.
We want our trees to have enough room to grow roots that can anchor the tree. Often, a large tree planted in a restricted root space will either not be as vigorous as hoped, or the tree may not have enough room for anchoring in high winds.
A recent study by the United States Department of Agriculture shows the average lifespan of an urban tree is only around 23 years. One reason for the short lifespan is the lack of adequate root space.
Assuming a soil depth of at least 3 feet, a small maturing tree needs at least 100 square feet of rooting space; a medium-size maturing tree requires at least 400 square feet; and a large maturing tree needs at least 900 square feet.
As we strive to create a more livable urban environment that includes trees, we need to consider roots and how our activities can affect how they function.
If we do a better job of creating and managing healthy tree root systems, we can have healthier trees that increase the quality of life in our communities.
For help with horticultural questions, contact your county extension office. Note that staff may be working outside offices during COVID-19. For extension information, visit ffl.ifas.ufl.edu.