Can I Sue a Neighbour For Trespass?
A Person Can Be Sued For Trespass. Trespass May Occur Accidentally or Intentionally. An Example of Trespass Includes Situations When a Neighbour Cuts Down a Tree.
Helpful Guide to Understanding Trespass to Property (Land) as Tortious Conduct
Trespassing upon property is commonly understood as a unlawful act in respect of the criminal law, such as in the context of a 'break & enter'; however, trespass to property is a civil law tort in addition to a prosecutable offence. As a prosecutable offence, trespass to property is addressed by the Trespass to Property Act, R.S.O. 1990, c. T.21 and the cases arising therefrom and perhaps the Criminal Code of Canada, R.S.C. 1985, c. C-46 depending on the relevant nature of the trespass. As a tort, trespass to property is very broad and involves presence upon and interference with the land of another as well, technically, could arise at any time an uninvited person enters upon the lands of another, or when invited, oversteps or uses the lands of another in an unauthorized way or as occurred in the case of Gross v. Wright,  S.C.R. 214 an effort to 'steal' the space of an adjacent neighbour. The tort of trespass to property may occur in many ways including innocently and accidentally such as cases where a property owner unintentionally crosses property boundaries without any illicit purpose such as occurred in the cases of Barnstead v. Ramsey, 1996 CanLII 1574 ; Sinkewicz v. Schmidt, 1994 CanLII 5148 where trees owned by a neighbour were mistakenly cut down.
Damages for Trespass
In many circumstances calculating the extent of harm caused by a trespass may be difficult. In other circumstances, involving a technical trespass without any corresponding harm, an appropriate redress for trespass is also troublesome. Generally, where trespass occurs without harm, a very nominal sum may be awarded. On the issue of trespass damages, the Court of Appeal addressed such at length within the case of TMS Lighting Ltd. v. KJS Transport Inc., 2014 ONCA 1 wherein, among other things, the difficulty to prove damages with exactitude was mentioned and it was stated:
 It is also beyond controversy that a plaintiff bears the onus of proving his or her claimed loss and the quantum of associated damages on a reasonable preponderance of credible evidence. Further, as the trial judge recognized in this case, a trial judge is obliged to do his or her best to assess the damages suffered by a plaintiff on the available evidence even where difficulties in the quantification of damages render a precise mathematical calculation of a plaintiff’s loss uncertain or impossible. Mathematical exactitude in the calculation of damages is neither necessary nor realistic in many cases. The controlling principles were clearly expressed by Finlayson J.A. of this court in Martin v. Goldfarb, 1998 CanLII 4150 (ON CA),  O.J. No. 3403, 112 O.A.C. 138, at para. 75, leave to appeal to S.C.C. refused,  S.C.C.A. No. 516:
I have concluded that it is a well established principle that where damages in a particular case are by their inherent nature difficult to assess, the court must do the best it can in the circumstances. That is not to say, however, that a litigant is relieved of his or her duty to prove the facts upon which the damages are estimated. The distinction drawn in the various authorities, as I see it, is that where the assessment is difficult because of the nature of the damage proved, the difficulty of assessment is no ground for refusing substantial damages even to the point of resorting to guess work. However, where the absence of evidence makes it impossible to assess damages, the litigant is entitled to nominal damages at best.
See also Cadbury Schweppes Inc. v. FBI Foods Ltd., 1999 CanLII 705 (SCC),  1 S.C.R. 142, at para. 99; 100 Main Street East Ltd. v. W.B. Construction Ltd. (1978), 1978 CanLII 1630 (ON CA), 20 O.R. (2d) 401 (C.A.), 88 D.L.R. (3d) 1, at para. 80; Penvidic Contracting Co. v. International Nickel Co. of Canada, 1975 CanLII 6 (SCC),  1 S.C.R. 267, at pp. 278-79.
The tort of trespass to property is extremely broad in potential application. As a strict tort, liability for trespass may occur even when the trepass was accidental; however, in the absence of illicit intentions or harm, it is anticipated that such an innocent trespass would yield very little damages. With such said, sometimes an accidental trespass without illicit intentions may still result in significant harm.