If you want to make a tree be the best it can possibly be, it takes a little work every year. As much as nature helps, no such thing as a naturally perfect tree. The concept that it's best to let nature take care of it isn't accurate. I'll explain more about that specifically in another post.
ISA standards are proudly followed by the best pruners and arborists, but there's a lot more to it than that. In some cases, you have to break the rules for the greater good. Knowing when to do this is an art. Since most pruners see it as a job and not an art, they usually fall short of the best results, usually by a large margin. It sometimes can be worse if a client dictates that they want things a certain way, or want a more conservative or aggressive approach than what is really the best long-term need
As far as what I strive for in pruning a tree perfectly over the long term, these are the goals:
HIDE THE EVIDENCE
The ultimate goal of any pruning undertaking should be to conceal all evidence that pruning ever took place. Overcoming this paradox takes great long-term planning. I once saw a Beech tree at a show that was renowned for its great balance and taper and lack of visible scars. It was as flawless as Grace Kelly. The tree was probably about 2 feet tall and at least 20 or 30 years old. This nearly perfect, natural-looking tiny tree was the result of meticulous, frequent, strategic pruning. Removing or pinching back a branch at just the right time will reduce or eliminate obvious scarring. Ideally, branches should be cut when they're small enough to heal/seal over within 2 or 3 years, or at least a relatively short time. Any branches over about 1-1/2" in diameter will leave scarring for years, maybe forever. However, if you cut back or remove branches too early, this can reduce tapering and induce sparse branching. This timing and balance is difficult for most pruners to achieve or even understand.
STRONG, TAPERED TRUNK
A thick, tapered trunk will reveal some history, strength and permanence. The trunk by virtue of its texture, shape and bark may also be the most interesting feature a tree has to offer. Careful long-term planning and pruning is needed to achieve a terrific trunk. Just like how our torsos are more important than our arms and legs. But thick isn't necessarily good for us. I have a ratio in mind, of between 20-to-1 and 30-to-1, of the height of the tree in relation to its trunk diameter near the base, tapering to zero at the top. This is good taper. Very young trees won't have this ratio unless you work really hard at it, but mature trees can almost all achieve this with the exception of some naturally stubborn skinny species. But even those species can be optimized. Older trees take on a ratio that may be more like 10-1 or less, which is really solid.
LACK OF DEATH, DISEASE, DAMAGE AND DANGER
Wouldn't we all like this? For various reasons, all trees have branches that just die. Some we can prevent, others we can't. Some branches get diseased or damaged. Some pose an imminent danger of breaking or otherwise causing destruction. We need to remove these as soon as possible. If we don't, the wind and gravity might do it for us, or disease can spread the branch itself. Removing death, damage, danger and disease should be the first step each time you prune. For whatever reason, real or perceived, a living branch can't exist if there's a dead one in the way. Removing dead wood tends to invigorate a tree.
WELL-DISTRIBUTED, TAPERING BRANCHES
This is where almost everyone misses the mark. Too often, you see a whole bunch of branches emerge from the same point about 6 to 8 feet off the ground, grow with inadequate tapering, proportion and angle, bypass important intermediate branches (ramification), and finish with a burst of most of the branches and foliage at the outer edges. Frequent, proper pruning will promote better distribution and balance, creating a far better-looking and healthier tree. Having this ramification is also important so that there is a replacement branch fairly close by in case another branch dies or otherwise has to go, thus reducing bare areas like in Charlie Brown's Xmas tree. Snoopy and Linus can't fix that problem. Only time and spiffy actions can, best case.
AVOIDING WHORLS AND REDUNDANCY
Whenever you see whorls (more than one branch coming out of the trunk or another branch in one spot), it's redundant. A trunk or branch should extend a bit before another branch emerges. Whorls create ugly bulges and eliminate attractive, staggered branching patterns that are much preferred. Some species naturally produce whorls, and in cases where the specie is naturally symmetrical, like a blue spruce or Auracarias, for example, you respect that look. In most other cases, like Japanese Maples, this inherent whorl pattern can and should be reduced or eliminated in the big picture for a more pleasing look.
TRUNK TO BRANCH SIZE RATIO
Simply put, the thickness or length of a branch should not "compete" with the trunk. The trunk is king, The ratio may be hard to target, but generally a branch should be no more than half the diameter of the trunk where they meet and depart. Length is harder to pinpoint. The closer you get to the top of the tree, the less dominant a branch should be. I frequently see White Birches where 3/4 of the way up, a branch emerges just way too thick and long. While this attribute in people might well excite their friends, once you start noticing it in trees, it will gnaw at you like a stain on a necktie, and may be where your eye goes first. In the case of a co-dominant leader, the trunk is nearly equally split in two, either from pruning an existing trunk to become two trunks, or from a branch getting a little too cocky and showing up the boss. More often than not, one leader is better than two. Japanese Maples are frequently trained to have two leaders primarily to increase their real or perceived width.
PROMOTING HORIZONTAL BRANCHING
Most trees look better and are stronger with a more horizontal rather than vertical branching pattern. Certain species, such as White Birches, tend to be more vertical. Even in these trees, doing what you can to enhance a more horizontal pattern is a good thing.
ELIMINATE OVERLY-STRAIGHT BRANCHING
The most interesting trees, aside from super-straight species like Coast Redwoods, have branches that curve or twist, a little or a lot. Valley oaks are most notable for this curvy growth pattern. Branches that keep going straight for a long distance tend to indicate under- or over-pruning, and it's just not very interesting. Proper pruning will promote some curvature, as well as good taper, strength and ramification. And vertical water spouts/sprouts, so often mentioned in my posts, are to be avoided at all costs once they get bigger than about a pencil.
BALANCE FOLIAGE DENSITY
This is a really hard ratio to pinpoint. It can depend on the specie, age, size, or preference. Essentially, you want enough foliage distributed throughout the tree, not just at the very outside, to avoid large voids, but also to allow light and air to penetrate. Japanese Maples are known for having a delicate, airy texture, with the branching being a large part of the appeal. Waterfall-type maples generally have more dense foliage, especially at the edges. Even in those cases where they look great, it would be better for the tree to be opened up a bit and retain some inner branching.
AVOID BLUNT BRANCH TIPS
Nothing is more obvious in pruning than when someone cuts the end of a branch tip off so that it's larger than about the thickness of a pencil, and in smaller or more delicate trees, less than that, perhaps 1/8 or 3/16". Now, during restorative pruning, some of this is unavoidable, but it's better to make it a long-term goal to keep all the branch tips tiny. FYI, cutting the tip off a branch is called a "heading cut". Some pruning guides discourage heading cuts, but they're not bad in all cases, and quite beneficial or even necessary in some cases. You just have to know when.
AVOID POLLARDING, TOPPING, LIONTAILING, MURDER
OK. In case you haven't caught my other articles, I frequently mention "Crape Murder". You need to have a good understanding of this, or you really won't understand good pruning at all. What this term refers to is when the branches are cut off very bluntly at the very outside, with the additional removal of most inner secondary branches. In the spring following this dastardly treatment, the tips of each of the blunt branches explode into multiple, up to a dozen or more, mostly vertical shoots that grow so quickly, long and skinny, that they can't support the weight of the coming flowers or even their own wood and foliage, and they flop over like a sad wet green and magenta noodle. This process is repeated year after year, and each year the tree looks a bit worse until it's utterly hideous. And the removal of all the inner branches over time left nothing to take over in case you want to remove some of these stocky branches. People prune other trees this way, but it's especially common in Crape Myrtles and Mulberry trees. Whatever convinced someone to prune this way, it's never a good idea and can't be justified in the long term. Liontailing refers to removing all inner branching and foliage so that all of it's on the very outside. Not good. Now, once you have this problem with your trees, it'a long process to repair with very diligent, thoughtful pruning that itself won't look great for a few years, but it's like heart surgery, cleaning your garage, or repainting a car. It gets a bit uglier before it gets better. At this point you can't take a conservative approach, and pruning and pinching several times per year is required to get things back on track until it recovers. Luckily, Crape Myrtles, Mulberries, and other vigorous trees that people torment this way are great at recovering from aggressive rehabilitation, even to the point where some trees are cut down to the ground to start all over.
Thinning is the most common cut. You take it a branch entirely or back to a point where a lateral branch will take its place. Thinning will remove mass if there's too much, or eliminate crossing, rubbing, oddly-directed or parallel branches. If you're removing a portion of a branch back to a lateral/descendant branch, then that branch that becomes the new tip should be at least 1/3 the diameter of that you cut off at that point. This will help keep taper appropriate, and also vigor in a branch that's too small may not be enough to sustain the growth, or the point of cutoff actually could explode in a pollarding style and then you have a we're lot of little branches to deal with. Whenever you make a thinning cut, or heading cut for that matter, new growth will tend to occur either from that point or further inside the tree, usually some of each.
LEAVE TEMPORARY BRANCHES
Some of the most important branches are the ones that are temporary. Technically, almost all branches are temporary, until new ones emerge and develop and older ones die or lose their importance. In many cases, we knowingly let branches stick around just long enough to do a task, knowing all the while that they're doomed within a year or two. Most notably, a branch may be needed lower on a parent branch to help thicken the parent in and around that point. But if we don't like it, we cut it off when it gets to about 1/4", and nobody realizes was there or removed. But if tree branch grows into something we like, we can just leave it. We may not particularly like the look of a tempest branch, but the long-term benefit may outweigh the immediate need for beauty.
BRANCH ORIGINATION ANGLE
Branches may come out of a trunk at almost any angle. They usually come out pretty perpendicular in a left/right orientation, and usually anywhere from 90 degrees (straight out horizontal) to nearly vertical. The closer to vertical it is, the weaker it will be, since the nearly parallel wood to the trunk can split easily. It's best to have an angle at least 30 degrees from vertical, and 45 is better. 90 is a bit much to ask for in certain trees. Many, if not most conifers have more horizontal branching. Though you can't do a lot to determine the angle a branch comes out, you can decide which branch among others close together has the best properties, and remove others that may be a problem. For pruning purposes, you can nudge the branch in a certain direction over time, but the origination angle is pretty well set in wood. Some trees that tend to naturally have more vertical branching, like European white birches, maybe the best you can do is just go for the branches that have a few degrees difference, provided all other deciding factors are equal. Bark inclusion is also a consideration. I'll go into that in another post, or you can research that subject on your own.
CHANGE THE SIZE OR SHAPE
You'll often be told that you shouldn't try to limit the size of a tree, but plant a tree that fits the space. That's mostly true, but you know we all prefer to pick a tree we like and live with the consequences. This happens more with shrubs than trees, so we shear them or cut them back so they don't rub against she house, etc. Trees will tolerate some of this, though shearing isn't usually practical or pretty. So then what? Well, you can control the size to a good degree, at least until it gets old. Then it becomes a lot harder and you should give up. If there's something that can be fixed, great. If not, don't butcher it, cut it down if it's a problem. But controlling the size has to start early in its life, or you'll end up with all sorts of proportionality and growth pattern problems. You simply can't wait until a tree is 20 years old, that you want to hold it to that size forever. There may be some exceptions to this, but it's not a good plan.
More to come............