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The recent snow events on trees on landscapes have resulted in the failure of many tree branches in the southwest Ohio region. The failure if these branches is predictable and with good training and pruning practices can help reduce these type of branch failure events.
Science of Branch Failures
When a tree branch fails its the result of the tree branch being loaded with too much weight(force) that exceeds the branch load capacity. These failure points are co-dominate branches that are of equal diameter or unions in a "v" shape.
During the events like ice/snow combined with wind and the addition of leaves on the branch cause the tree branch is bent and pulled and the branch will split through the center axis of the tree branch. Many cases these failures are a direct result of poor branch taper. Keep in mind tree branches from tension wood(upper portion of branch) and tension wood ( lower branches) of the tree branch. Poorly tapered branches are more subject due to inadequate wood formation the compensate for the dynamic loading.
Preventing Branch Failures
In the field, practitioners should consider the strength of codominant stems and attachments where branch diameter is roughly 70% of trunk diameter to be roughly one-half as strong as an attachment that includes a clearly subordinate branch.
There is no way, except for complete enclosure, to protect trees from all storm damage. Trees are not adapted to worst-case storms only to our average wind climate. Listed are several things to minimize the main types of storm damage:
Let trees adjust to the wind environment. Tight staking and guying from the time of planting holds a tree in place while preventing internal adjustment to wind loading. Always stake and tie the tree loosely where the stem can move and bend in the wind. Keep ties in place for a few growing seasons to insure a well-established root system. Continue to loosen and eventually release the ties. The support stakes can be left in place to protect the stem from mechanical damage. After five to seven years, remove all tree support. The tree will continue to grow and adjust to its new environment.
Practice proper pruning techniques by cutting branches before they become larger than one inch in diameter. The branch collar should not be damaged . The branch collar is part of the stem and, if damaged by poor pruning, provides an avenue of attack into the main stem for pests. Proper pruning minimizes a number of structural problems that occur in association with new wood growth around a pruned branch.
Eliminate codominant branches. Prune forked branches and branches that arise opposite each other on the stem early. Cut one side off now to prevent losing the whole tree later if it splits in a storm. In trees with opposite branching patterns, such as ash or maple, proper branch training is essential for a long-lived, storm resistant tree.
Keep trees as healthy as possible with timely watering and proper fertilization. Healthy, vigorous trees adjust more quickly to changes in the environment, are more wind firm, and react more effectively to damage.
Do not over fertilize the tree with nitrogen or over water the soil. This can increase the crown surface area and/or decrease the rooting area. This type of biological change makes the tree susceptible to storm damage.
Eliminate lopsided crowns. Prune branches to produce a reasonably symmetrical crown. If more than 70 percent of the crown is on one side of a mature tree, consider tree removal and replacement. Guying and bracing branches are last-ditch efforts when a tree has to be saved in spite of itself.
Remove or treat pest problems, like branch cankers, to minimize potential damage. Do not over-treat tree hollows. Do not remove decayed wood from hollows unless it falls away in your hands. Cleaning hollows can lead to further internal damage. Cover the opening to hollows to allow the tree to grow over the opening, prevent animals from expanding it, and to keep water from running in.
Keep the tree growing upright with one main stem. Prune away branches that compete in height with the main stem. Eliminate branches with tight or narrow crotches.
Install lightning protection systems on historic, rare, specimen or recreational area trees. Consult a qualified arborist or urban forester to insure adequate design. Lightning protection systems are covered in detail later in this publication.
Continue to promote wind firmness by not overcrowding trees and by proper guying and bracing. A tree must always be able to move in the wind. Do not keep a tree tied into position with tight cables. In a stand of trees, slowly remove trees over a number of years to allow wind firmness to develop in the remaining trees.
For more information see this https://www.extension.purdue.edu/extmedia/FNR/FNR-FAQ-12-W.pdf