Most boundary tree disagreements never reach a courtroom. Three published Ontario decisions each turned on a fact a homeowner could have documented in advance: where the trunk sits, the tree’s condition, and the cost of damaging a tree that was not yours.
For the statute and common-law framework these cases sit inside, see our guide to neighbour tree disputes in Ontario.
Hartley v Cunningham: A Trunk Can Cross the Line Above Grade
Ontario’s Forestry Act (R.S.O. 1990, c. F.26) makes a boundary tree the common property of both owners under section 10(2), where the trunk grows on the property line itself. Section 10(3) makes it an offence to injure or destroy that tree without both owners’ consent. Hartley v Cunningham settled what counts as the trunk, a question the statute leaves open.
The court read the word broadly, covering the whole stem from the roots up to where it branches into limbs and foliage, rather than only the point where it meets the ground, and the Ontario Court of Appeal upheld that reading in 2013 (2013 ONCA 759). A tree with a base sitting entirely on one owner’s side can still be common property if the trunk leans or forks across the line higher up.
Section 19(1) sets the penalty for injuring or destroying a boundary tree without consent at a fine of up to $20,000, imprisonment for up to three months, or both. Deciding a tree is “clearly” on one side based on where it enters the soil, without checking where the trunk sits further up, is the kind of assumption Hartley v Cunningham shows a court will not accept.
Freedman v Cooper: A Documented Hazard Beats a Refusal to Consent
The Forestry Act’s consent requirement assumes both owners agree before a boundary tree comes down. Freedman v Cooper tested what happens when one owner refuses and the tree is dangerous: a boundary Norway maple lost a third of its canopy in an ice storm, two separate arborists reported a continuing risk, and one co-owner still would not consent to removal.
The Ontario Superior Court held in 2015 that nuisance law, not the Forestry Act’s consent requirement, governs a hazardous tree, and ordered the objecting owner not to interfere with removal (2015 ONSC 1373). The consent requirement still exists. Once the hazard was proven, a different legal test displaced it.
It took condition reports from more than one arborist to establish the risk, and a court application to enforce it. A neighbour’s opinion that a tree looks unsafe does not carry the same weight as a written risk finding. A TRAQ-based tree risk assessment is that kind of written risk finding.
Murphy v Mullen: What Damaging a Tree Costs
Murphy v Mullen sets what a court awards once a tree has been damaged. It is not a boundary ownership case. The Ontario Court of Appeal’s 2021 decision put the number in six figures once replacement, restoration, and lost screening value were counted (2021 ONCA 872).
The common-law self-help right to prune back an overhanging branch or root has two hard limits: no stepping onto the neighbour’s property to do the cutting, and no cutting that kills the tree or leaves it structurally unstable. Murphy v Mullen shows the cost of crossing that second limit. A dispute over a few overhanging branches is a pruning question with a defined boundary. Removing or seriously injuring a tree that turns out not to be entirely yours costs far more, whether it is a true boundary tree under the Forestry Act or grows on the other side of the line.
Document the Tree Before a Dispute Starts
Before a dispute starts, get a condition assessment and a risk report from an independent arborist, and take dated photographs of the trunk’s position relative to the fence line. A lawyer asks for that record first.
Document the tree before construction too. A tree protection zone is measured outward from the trunk, not from the property line. If that zone overlaps a construction disturbance area across the fence, the tree belongs in the project’s protection plan, a scope question our guide to trees you don’t own covers in more detail. A construction arborist report maps that before a design is finalized rather than after equipment shows up.
If a neighbour has already sent a lawyer’s letter, or a tree has caused property damage, hire a lawyer. An independent arborist report gives that lawyer, or the neighbour, a written finding in place of two conflicting opinions about the same tree.