Today I attended an Arboricultural Association workshop presented by Dr. Duncan Slater entitled Assessment of Tree Forks.
I thought I should share my take on it as I find it very important for people in my industry to consider these things.
The workshop is based on research by the above doctor and his associates. There were many points raised, but what I found most relevant to myself and I believe to anyone inspecting and/climbing trees in a commercial manner, are the uses of terms such as compression forks and tight unions to denote high risk of failure unions. It was proven that there is no compressive force pushing forks with included bark apart and that a fork with an acute angle does not necessarily mean that it is weak or without a branch bark ridge/with bark inclusion. Weak forks are most often formed when little or no pressure is exerted on their apex/top but this is usually because they are supported higher up in the canopy by crossing/rubbing branches or/and actually fused branches. A weak fork will not fail if it is supported.
What this means in practical terms is that one should think twice about crown cleaning crossing branches despite the commonly accepted practice to remove crossing branches because they can lead to branch failure.
This also means that if supporting branches decay, the fork must build sufficient reaction wood before it is subjected to a force strong enough to make it fail. The period before it has done this is when such forks are at the highest risk of failing. Some forks with included bark will never be able to reinforce themselves sufficiently, but these types of forks can be identified.
It is important to know your forks when working with trees and this has helped me be more confident in my tree assessments.
For all the references, you will need to attend the workshop as there are too many for me to cite here at this time