Man Versus Tree
by Mary Ann Buenzow and Mary Thompson

Each time a tree is wounded there is potential for infection by microorganisms.

Mower damage

When you run into a tree with a lawnmower you are creating wounds that have the potential to permanently damage or even kill a tree.  Wounds, whether done through carelessness or ignorance, draw on a tree's resources during the healing process.  The wounded tree will attempt to heal itself.  Depending upon it's overall condition and the season, the tree could be so compromised that the demands of healing could permanently weaken it and it could eventually die.      Wounded trees are prone to infection by microorganisms.  If you have no training in tree care or pruning, call an arborist or do some homework before making that first cut.  Put mulch rings around lawn trees to avoid mowing near the trunk.  (BUT:  Don't over-mulch or make “volcanos” of mulch around the trunk, where excessive moisture can cause root collar rot.)

Over-pruning

These trees appear to have been over-pruned at maturity, apparently to allow sunlight to reach the building.  The pruning has eliminated a large percentage of the crown, making it difficult for the tree to maintain it's current level of growth.  Within one growing season, these trees will be sprouting from the trunk and main limbs (called epicormic branching or water sprouting) in an attempt to recover the foliage that was removed.  Pruning should focus on improving overall form by removing multiple low and poorly-angled branches, crossing branches, and other conformation defects, a process best done while trees are young and developing their form.

Trees that are dramatically pruned, like these, may suit the homeowner's idea of a clean look , but the fact is removing over 40 percent of the canopy can do irreparable damage to the health of a mature tree.  Shaping should begin early, not at maturity or when the limbs are over 2" in diameter.

The Right Tool for the Job - or - Don't use a chainsaw to trim a tree

Chainsaws have a place in tree maintenance - usually at the end of a tree's life - when it is being felled.  These trees show extreme over-pruning - probably with a chainsaw - that will almost certainly kill them over time due to the stress of trying to recover from the wounds.  The tree on the right shows knots of heavy callus where previous large pruning wounds have healed.      When pruning the rule-of-thumb is that no more than one-third of the live branches should be removed in one pruning cycle (usually one to two year cycles on young trees).  Also, it is best to remove branches before they reach 2 inches in diameter.

Topping

These five trees are victims of "topping", a destructive pruning technique that permanently weakens the canopy and can cause death if severe enough.       People often top trees in a misguided attempt to shape the tree, to thicken the canopy or to control the height growth.       The trees shown here are sending out shoots in an attempt to create enough canopy to survive.  These epicormic sprouts are weakly attached to branches that will eventually die back to the next lateral branch below (where they should have been pruned to in the first place!).

Vandalism

These are two of five bur oaks deliberately vandalized at Magnolia Bluff park.     In an act that must have taken hours to accomplish the vandals carved “our hearts are yours” through the bark and into the wood.     The trees appear to be recovering but their future cannot not accurately assessed.  Decay fungi have probably entered and could weaken the trees over time. The wounds show callus around the outer edges of the letters, but the exposed wood is showing cracking, splintering, insect infestation, and weathering.

Not all damage is deliberate

In an act all too often found in parks and areas where people congregate, these trees were girdled with ribbons, probably left behind after a celebration.  Still strong after literally years, the ribbons are now cutting off nourishment to the limbs which may eventually die of weakness or starvation.

Think before you act

This tree is dead.  It may look alive, but it is doomed to die as the result of the grevious wounds inflicted on it by whoever cut off its large surface roots.   Apparently the person who chopped away the roots of this tree, perhaps to effect a sidewalk project, or a flower bed, didn't stop to think that the thin layer just under the bark is what feeds the entire tree.  Cut off from nourishment the tree will eventually fail and die.