You may prune your tree, but you cannot damage your tree. Under the tree management bylaw, trees on private property are protected from being ‘damaged’ in a way which creates hazards for the homeowner and the community. Improper pruning practices such as ‘topping’ or ‘pollarding’ is considered damage and the homeowner may be subject to fines from the City.
If you wish to prune your own tree, consult the Best Management Practices (BMP’s) of the International Society of Arboriculture (ISA) first to ensure no damage comes to your tree. To ensure proper pruning methods, hire an ISA certified arborist to ensure its health and longevity while training the tree to grow to a desired form.