While an insurance broker, Scott McEachern founded and managed TREESURE, a national insurance program customized specifically for tree workers and consulting arborists. During this time, Scott frequently provided risk management consultation to tree workers and arboriculture consultants while also gaining in return knowledge of many tree risk concerns facing the arboriculture profession as well as general property owners as the owners of trees.
Although trees are extensively found throughout our urban and rural landscape, we often take the value of trees for granted. We also often fail to fully appreciate the potential for legal issues to arise from incidents involving tree ownership or tree management. Among other things, legal issues may involve border trees, hazard trees, healthy trees, or nuisance trees.
Owners of trees, or others responsible for such trees (such as hired maintenance contractors), generally face liability only when it was known, or constructively known, that a tree failure risk was present and the owner (or others) failed to properly tend to the tree. In this way it can be thought that the injury or damage was a result of the delay in caring for the tree rather than the result of the risks inherent in a tree. Essentially, the negligent 'failure to maintain' is a man-made risk rather than a natural tree risk. On the point of liability for failure to maintain trees, the Superior Court of Ontario (Divisional Court) said in Hallok v. Toronto Hydro Electric System Ltd., 2003 CanLII 8519 at paragraph 14:
It would appear to be common ground that a property owner, such as Park Lawn, cannot be held responsible for damage resulting from a limb on a tree falling simply on the basis that the limb or tree fell. If the evidence does not establish that there was knowledge on the part of the defendant, Park Lawn, of a dangerous condition of a tree or that there was a dangerous condition of which the defendant Park Lawn ought to have knowledge, a finding of negligence is unavailable as a matter of law. (See: Culley v. Maguire,  O.J. No. 52 (C.A.) at p. 1; Quinlan v. Gates,  O.J. No. 5292 (S.C.J.) at p. 2; Buttoni et al. v. Henderson et al., 21 O.R. 309 (H.C.J.) at p. 371; Doucette v. Parent,  O.J. No. 3493 (Gen. Div.) at p. 4;Gasho v. Clinton (Town),  O.J. No. 4505 (S.C.J. (Small Claims) at p. 4).
As such, it seems that knowledge, or constructive knowledge, of a dangerous condition is a requirement of liability for negligent maintenance of trees. Note that "constructive knowledge" is knowledge which the law deems a person ought to have based on reasonableness. If a reasonably diligent person would know of a dangerous condition this is "constructive knowledge" and proving actual knowledge becomes unnecessary. Constructive knowledge is often much easier to prove than actual knowledge. For example, following severe storms, property owners should reasonably be on alert for broken branches (known in arboriculture circles as "hangers") as well as other dangerous conditions. Additionally, it is important to recognize that intentionally avoiding investigation and thereby choosing to remain unaware of a dangerous condition may be deemed an act of willful blindness from which constructive knowledge may also be imposed.
Neighbour disputes involving trees often involve debate over ownership, and therefore decision making power, involving trees whose trunk rests upon the property line. A tree upon a property line is jointly owned by each neighbour and as such any decisions as may affect the well being of the tree require mutual agreement. A neighbour that makes decisions without consultation or agreement may become subjected to litigation seeking compensation for wrongful trespass. In such cases, the valuation of a tree may be highly subjective involving criteria beyond simply 'wood' value.
Hazard Trees (including attractive nuisance)
The ownership of trees brings legal risks relating to public safety as similar from other realty property ownership risks borne out of the Occupier's Liability Act.
Although hazard trees are generally presumed only as unhealthy and structurally failing trees, much can be said for serious risks posed by fully healthy trees.
The legal concept of nuisance involves interference by a person (or persons) with the reasonable enjoyment of property of another person (or persons). The list of ways in which someone can interfere with anothers property is extensive and trees are sometimes are the cause. Trees can cause nuisance by shedding debris, by invading roots, or other inherent concerns.
While tree owners should take proper care to reduce or eliminate the risk of nuisance to others, the law of nuisance is generally deemed that where strict liability applies. Accordingly, liability for damage caused by an interfering tree can arise regardless of the level of care taken by the tree owner. Furthermore, a neighbour whose property is affected by a nuisance tree may have right to 'self help' so long as no trespass occurs during the efforts to remedy the nuisance such as the destruction of invasive roots, even if the method of 'self help' results in mortal injury to the tree.
As above, the value of trees may be highly subjective. When someone has damaged or destroyed the tree of another, the tree owner often takes the position that loss of the tree involves much more than the loss of 'wood' but also loss of various benefits previously enjoyed by the presence of the tree. Valuation factors involving trees may include consideration for loss of amenities including shade, privacy, windbreak, and other intangible aspects. Arborists certified as appraisers by the International Society of Arboriculture or American Society of Consulting Arborists can provdie reasonable valuations by using professional standards such as the 'CTLA method' of valuation.
Expert Witness Report
For inspection, assessments, and valuations, on tree liability issues contact:
Richardson Tree Care
Michael Richardson, ISA Board Certified Master Arborist
P: 613 475 2877