Unless there is legislation or restrictive covenants to the contrary, the current common law regime allows “each property owner, within the boundaries of his or her own property, to do as they wish. This is so both with respect to planting trees, which may tomorrow block a neighbour’s view or spill onto a neighbour’s property, and with respect to pruning or cutting the overhanging branches or roots of trees that cross a property line”. In other words, your neighbour may simply cut any part of a tree (with its trunk on your land) that crosses over the property line and overhangs onto his property.
Pursuant to the Ontario Forestry Act a “boundary tree” (a tree whose trunk straddles a property line) is the common property of both property owners and cannot be injured or destroyed without the consent of both owners. “Trunk” is not defined in the legislation but a recent case held that “trunk” should be given its ordinary dictionary meaning i.e. it is that part of the tree from its point of growth away from its roots up to where it branches out to limbs and foliage.
Every person who injures or destroys a tree growing on the boundary between adjoining lands without the consent of the land owners is guilty of an offense. The penalty is a fine of up to $20,000 or imprisonment for up to three months, in addition to any civil remedies.