Thank you to the Alaska Forestry Service for much of the information contained in this post, and for the graphic included.
Pruning trees to remove dead branches and other ladder fuels is just one way to make your landscape Firewise.
Proper pruning can improve the appearance and condition of a tree, however, keep in mind that every pruning cut is a wound that can alter the growth of the tree. Trees do not heal in the same way animals do; they grow over and compartmentalize wounds, which remain with the tree for the rest of its life. Making improper cuts can cause permanent damage. Trees get their energy from food they make in their leaves through the process of photosynthesis. Every pruning cut that removes live foliage decreases the tree’s ability to make food and energy to support itself and grow.
It is important that no more than one quarter of the live foliage be removed in one growing season, so that the tree can produce enough energy to close pruning wounds, defend itself against insects and disease, and carry out life processes. If you have a smaller tree from which you want to remove lower branches to allow clearance or remove ladder fuels, it may take a few years and multiple pruning sessions to achieve the desired final crown height.
The best time to prune trees is during the dormant season, or in the middle of summer. Avoid pruning during the spring when the trees are beginning to leaf out, and the fall when they are dropping leaves.
Spruce beetle adults are searching for new trees to lay eggs in during mid-May through mid-August, so do not prune spruce during that time. When removing long branches that are greater than two inches in diameter or those that you cannot easily support by hand, it is best to remove the weight of the branch before making the final cut. This prevents the branch from splitting and the bark tearing causing injury to the branch collar and trunk. Make the first cut on the underside and a third of the way through the branch eight to ten inches out from where the branch attaches to the trunk or another branch.
Make the second cut on the top of the branch, an inch or two further out from the first cut so that the branch snaps off leaving a stub.
The third and final cut is made just outside the branch collar, the swelling at the base of a branch where it enters the trunk or a larger branch. The branch collar is the tree’s defense zone against decay and should always be preserved in any pruning cut. When a proper cut is made, the collar will grow over the wound creating a circle of callous tissue and eventually seal the wound.
To reduce the length of a branch creating more space between trees and shrubs, shorten the limb back to another branch that is approximately the same size as the branch being removed. To make this cut properly you may need to remove the weight of the branch first. The final cut will be on an angle, almost parallel to the branch bark ridge (the ridge of bark in the crotch between the branch and stem). If it is necessary to remove more than half of the foliage on one branch, it is best to remove the entire branch.
Pruning can generate a lot of debris that should be disposed of properly so that it will not become fuel for a fire. It can be chipped and used for mulch or used as firewood and kindling. If you dispose of it at a trash transfer center, please learn and follow the rules for the proper disposal of green debris.