Home > Tree structure basics > Strength of different parts > Junctions > Branch unions dissected
Branch unions dissected
Unions
on branches that remain small compared to the trunk develop overlapping wood
collars (collars do not form on codominant stems). The result is a strong connection
between the branch and the trunk. The photo on the right shows a union where
trunk wood was entirely decayed away. The ridges of wood are the annual branch
collars that formed around last year's trunk wood. There are about 11 collars
clearly visible with several older collars decayed away and missing. I often
use the analagy of a lag screw inserted into a piece of wood to illustrate branch
connections. In this analagy the branch is the lag, the collars are the threads
of the lag, and the trunk is the piece of wood. Just as it is difficult to pull
a lag out of a piece of wood without unscrewing it, it is difficult to pull
a branch from a trunk that is small compared to the trunk. Note that there are
no collars present in the union below; that is the reason it pulled out of the
trunk. Unions with bark inclusions fail in
this pattern.
