Shade trees in landscapes and parks throughout Wisconsin are often in decline as a direct result of preventable human actions. Knowing just a few key tree biology facts and guidelines when working around trees goes a long way to keep trees healthy.

Two key structural systems are essential for proper tree function and growth. First, the root system. Most tree roots used for uptake of water and nutrients from the soil are shallow, typically only 12 to 18 inches deep, and require oxygen to grow. In addition, tree root systems extend in area out as far as the branches (to the dripline) and beyond.

Tree root systems are sensitive to changes and disruptions around them. Examples include digging and directly injuring roots, compacting soil over root systems with equipment use, adding soil fill over root zones, changing overall drainage patterns around trees, and misuse of chemicals. Tree decline usually is not immediate when these events occur and often may not show until years later. Use extreme care when doing any work around trees and protect the entire root zone, not just the area close to the trunk.

The second key structural system of trees is vascular tissue. Vascular systems include xylem tissue, to transport water and nutrients up from the roots, and phloem tissue, to transport food products (energy) within the tree. Since this vital network is located just under the bark, it is prone to injury from digging or using power equipment near trees, lawn mowers and trimmers, being struck by vehicles, and chains or clothes lines tied around trunks. In most cases, this injury is preventable.

Mowing and trimming equipment damage leads the list of preventable causes of tree damage. Use care when mowing and trimming near trees this season. Consider eliminating grass adjacent to the trunks of trees, mulching the area instead.

When dieback and thinning areas appear in up tree canopies, the first place to look for clues as to why should be down to the base of the trunk and area over the root zone. Injury to root systems and trunks typically results in dieback of the upper portions of the tree. Examine the trunk for wounds such as from sources listed above, with wood rot fungi often developing after wounds occur. Also look for a natural flare where the trunk enters the soil. Trunks going straight into the ground like telephone poles could spell problems such as soil fill.           

Work cautiously and consider protecting both entire root zones and trunks of trees. Taking a little time to do so helps ensure healthy trees for years to come!