Last month Washington state got walloped with snow and sustained extensive tree damage as a result. Branches, stems, and entire trees were pulled down to the ground under the weight of accumulated snow and ice.

Many of our trees were not adapted to that degree of stress, especially west of the Cascades where snow is less common. This means trees that were otherwise healthy and strong may have been damaged, and yet, as we should come to expect, it is the unhealthy and/or unstable trees that broke first.

This callery pear (pyrus calleryana) had three co-dominant stems and peeled like a banana under snow load. Photo by Ben Thompson/DNR

Here in Thurston County, DNR Urban Forestry staff observed many tree failures associated with the following defects:

  • Stems or branches weakened by decay
  • Co-dominant stems or branches with narrow branch unions and included bark
  • Stems and branches with low taper extending out beyond the furthest extent of the canopy, leaving the ends more exposed

The tragic irony here is that many tree defects are often visible to the trained eye, and could have been addressed by pruning prior to the storm(s).

If whole trees came down, then removal is the only unfortunate solution. Trees with broken stems or branches may still be retained in the landscape, but some proper pruning should be done to facilitate trees’ recovery.

Stubs of broken branches still attached to the tree often have splintered or jagged ends. This leaves a lot of exposed surface area among the remaining wood fibers for airborne bacterium and fungal spores to colonize, which increases the likelihood of future decay.

Proper pruning cuts can reduce the exposed area of damage and bring damaged limbs back to a union with an un-damaged (or less-damaged) branch, or the trunk. This pruning approach to restore a storm-damaged trees and increase their chances of recovery is aptly known as ‘Crown Restoration Pruning’.

Crown restoration is considered an advanced pruning methodology and is best left to the professionals to perform correctly. Always work with an ISA Certified Arborist to ensure trees are pruned properly, safely, and in accordance with best practices.

Pruning cannot repair this failure but could have helped prevent it. Photo by Ben Thompson/DNR.

Of course, proactive pruning to remove or prevent weakened tree parts is always preferred.

Cities with established urban forestry programs should have or be working toward a regular, annual pruning cycle. Nearly all of the major utility providers in Washington use a program of ongoing and cyclical pruning to prevent tree-related outages before they happen.

As those of you who still lost power know well, pruning cannot prevent every potential tree failure. However, losses to trees and other assets can be minimized with proper and proactive pruning.