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Branch Collar - The branch collar and trunk collar are collectively called the branch collar. Where branches meet the trunks of most trees, there will be a series of collars. Each year two new collars will form. One collar is a trunk collar and the other a collar which is made up of branch tissues. Collectively we call them the branch collar. These collars are what support the astronomical weight of the branch (cantilever). Note, when looking at a tree from the outside, the two collars are often spoken of as the branch collar, e.g., “do not remove branch collars when pruning”

NOTE: This is a pull apart diagram of three growth increments. The collars are actually tight against each other. 1,2 and 3 represent growth increments. A in growth increment 1 represents the branch tissues. The tissues do not end abruptly as drawn, but they mesh with the truck tissues below the branch. B in growth increment 1 shows the trunk collar that envelopes the branch collar. (SHIGO 2002)

SOME MYTHS ON COLLARS from (SHIGO, 1993). Myth 22. THERE ARE NO SUCH THINGS AS BRANCH AND TRUNK COLLARS. Branch collars and trunk collars are shown on left in paper birch. The collars are collectively called branch collars. Anyone who has split wood has seen thousands of the collars, yet some people say they do not exist. Some people have seen the pull-apart diagram of the collars (above) and thought that that is the way they are in the living tree. Not so! In the tree the collars join and overlap as shown here. (See SHIGO, 1991 86-90) (See SHIGO, 2002 for top quality images)

See the top quality book "A World Wide Pruning Guide".