Most shade trees do best with a single dominant trunk. When side branches grow rapidly and become almost as large as the main trunk, they should be shortened or removed. If the tip of the original main leader or trunk becomes damaged, leave one upright growing branch to become the new leader and shorten or remove all others which are trying to become leaders.
No more than one-fourth to one-third of growth should be removed with any single pruning. Any pruning that requires a ladder should be reserved for a licensed, certified arborist, especially if utility lines are nearby.
Allen Wilson is a Vancouver gardening specialist. email@example.com