The art & science of trimming for safety, structure & design.
The primary goal of proper trimming is not to prevent breakage, but to try to avoid major failures. In other words trees trimmed and maintained properly and periodically, should be self pruning without major breakage or uproot. The obvious solution to the tree butchers, especially in the not so distant past, was to just cut everything. If the tree was falling apart, just cut all the limbs off, or cut the tree down. Believe it or not we still have essentially the same problem. In most communities now they have tree programs that prohibit butchering. However, hazard trees are even more of a problem because trees trimmed improperly are often more dangerous than if they were left alone. Inevitably, mature trees reach the stage where they start to break down. It's only natural. Consequently, most are terminated simply because of the absence of any evidence of the true science of arboriculture and\or anyone capable or knowledgeable enough to perform the right kind of maintenance. Any one can cut a tree down. The only requirement is a stump. How many things get broken or people killed in the process, is just an after thought.
So, we want to look at the very basic principles of tree safety, structure and design.
First, it has to be Natural. Nature is the best teacher. "Never does Nature say one thing and wisdom another."
Second, we need to understand all the dynamics of wind and snow and ice.
Third, we need to understand all the various aspects of the structural integrity of the tree. The type of wood, limb formation, defects, etc.
Fourth, we need to know how everything around and within the tree affects the way it grows and responds. Every cut you make has a short and a long term affect. No matter if it's in the tree or near the tree.
Then you need to be aware of anchorage. How well is the tree anchored now and later.
Now, let's look at this a little closer.
What is Natural? Obviously, there are many grand specimens that have never been trimmed. Except by Mother Nature! What are the key factors?
Number one. Preserve and promote the lower limbs. The most common assault on trees these days is ravaging the bottoms of the trees. It's only human to cut the lower limbs. Not only is this unnatural, it creates serious issues. The lower limbs stabilize the tree and deflect the wind over the top. If a tree looks top heavy, "it is!" If a tree can retain it's canopy right down to the ground and dominate it's space, it will be tremendously stronger, healthier, safer, live longer, and be more productive. The lower limbs shade the root zone, and eliminate the competition. Trees are the answer, not shrubs, and turf, and yard ornaments, etc. So many times I've seen trees neglected. [A lot of times just because people didn't know there was any such thing a proper care and maintenance.] Only to be cut down and replaced with shrubs and turf and decorations and more air conditioning. All high maintenance. We need to keep the lower branches where we can. This will do more than anything to keep our arboriculture standard high.
Number two. Is the tree shaped for wind and lightning resistance? As we just stated. The lower limbs deflect the wind. As you will see. All these things are interrelated. However, now we want to look at how to train the top of the tree. Is it natural to top trees? As we just said, "Cutting the bottom limbs is unnatural." The worst thing that is happening. Mother Nature will often top trees. This is natural. Anything that grows straight up is vulnerable to wind and lightning. The best strongest specimens that survive, spread out with a low profile.
Number three. Identify and adjust structural defects and malformations. If trees are trained from the beginning with a natural strong design in mind, you would never need anything more than a hand saw. Some of the best survivors have never been trimmed. The large majority though need help. Most tree failures are predictable. Often times serious defects are neglected beyond the point of saving the tree.