Tree repair or, formerly, tree surgery is a mechanically assisted method of reinforcing weak trees or putting split trees back together so that they will have added years of life.
The splitting action usually occurs where the main trunk breaks up into multiple stems. The key factor is how the crotches are formed; tight V-shaped crotches are usually the culprits. This type of crotch, sometimes called codominant, does not form with a naturally strong, fully formed branch collar, but exhibits included bark. Where the collar would have been has now been included inside the tight V-crotch along with a pocket of bark, sometimes severely impairing the crotch's holding power.
When the tree receives heavy wind or snow loading, these potentially weak crotches can open up very easily and split the trunk below the crotch, sometimes for several feet.
An early snowstorm in September 2012 had severe consequences for many mature trees in Calgary.
Usually what we see on first inspection after the storm is one part of the tree still standing while the other is lying on the ground, revealing the fresh white inner wood of the trunk, which is never supposed to be seen. The broken section will usually be bowed over and how and where it lies is a crucial determiner as to whether it can be repaired or not. You can safely say that a tree wears its heart in its skin — the bark.
So many important tissues and connections are in the bark that the easiest way to kill a tree is to girdle it (i.e. remove a wide strip of bark from all the way around the trunk). A bark inspection is the first thing we do to determine weather the tree can be saved. The bark tissues are very flexible and as long as they have not been crimped, folded and thus cut, a successful repair can usually be performed.
The size of the fallen split section is crucial; if it is too heavy, it may split the remaining bark attachment at the trunk when lifted. If you prune too many branches away to lighten it, you may impair that section's ability to feed itself; too much leafy branch loss means not enough energy production.
After all this has been determined, it is now time to raise the fallen section. I do this with a come-along secured about ⅔ of the height of both the split section and the remaining standing trunk.
Many times it is amazing, especially if the repair happens as soon as possible after the split, to see a near perfect fit, as if it hadn't been split.
Once the split section is back in place, I usually secure it with a rope in case anything happens to the come-along. I now have a second back-up holding line.
The next step is to decide where to drill through both sections so that a bolt or piece of threaded rod can be installed, permanently securing the split sections back together. The bolt should be as close to the top of the split as possible; installing it lower leaves some play in the system that could eventually get loose. The bolt should be placed dead-centre in the middle of the trunk. Now it is time to drill the hole through the trunk; for shorter holes you can use a brace, but for anything over a few inches long it is much better to use an electric drill. I use a ½ inch Milwaukee which has lots of torque. For smaller jobs up to approximately 1 foot I use ⅜ inch rod and bit diameter. For anything longer I use ⅝ inch rod and bit.