“Every tree whose trunk is growing on the boundary between adjoining lands is the common property of the owners of the adjoining lands.” Ontario Forestry Act (Section 10.2.)
If you live in Ontario and have a tree on your property and its trunk extends across your property-line, then according to the Ontario Forestry Act you have a boundary tree. The tree is therefore “common property.” The important issue: it is the “trunk” which must extend across the property line. The roots and canopies of trees can also cross property lines, but in this case, it is the trunk that is key. In 2013, the Ontario Superior Court provided a legal definition of a tree’s trunk. It is everything between the following two points:
1) from the root-collar to 2) where the first branch appears.
Note: the root-collar is where the roots begin. These may be above ground as well as underground and therefore may not be fully visible. If any part of the tree’s trunk from root collar to first branch—whether it is visible or not—crosses the property line, then it is a boundary tree. A tree’s trunk does not have to cross the property line at any particular point—it just has to cross at any point between the root collar and first branch.
Photos of boundary trees are also available here and can help you discern whether or not your tree is a boundary tree.
The 2013 legal definition of a shared tree is not based on a percentage. Even if 99% of the tree’s trunk grows on one side of a property line, the 1% growing on the other side of the property line still means the tree is a boundary tree and is therefore co-owned.
If a tree grows close to the property line and a property-owner wants to protect or cut it down, he or she should have a professional survey done to clearly establish where the trunk is in relation to the property line. This is not always something that is obvious or visible. It is a potentially expensive legal mistake to claim that the base of a tree (as it appears to the naked eye at ground level) is the determining factor. Once again: it is important to remember that if ANY part of the tree’s trunk crosses the property line it is co-owned.