1) Elements of Liability

There are a number of essential elements to the tort of trespass to land. The intrusion onto the land must be direct. This requirement is common to all torts of trespass. Mann v. Saulnier [Note 108: (1959), 19 D.L.R. (2d) 130 (N.B.C.A.).] provides a good illustration. The defendant in that case built a perpendicular fence on the boundary line between his and the plaintiff's property. In the course of time and weathering, the fence leaned marginally over the boundary line and into the plaintiff's airspace. It was held that there was no liability in trespass to land because the intrusion was not direct. [Note 109: Additionally, there was no intentional act or negligence on the part of the defendant.] The element of directness diminishes the power of trespass to land to deal with some environmental pollution. Oil spills that wash onto the plaintiff's land, waste that is carried down rivers to the plaintiff's land, and herbicides, pesticides, and airborne pollutants that drift in the wind to the plaintiff's land are likely to be regarded as indirect interferences with land. Damage caused by indirect interference may be actionable as a nuisance.

The defendant's interference with land must be intentional or negligent. The burden of proof is, however, on the defendant. The plaintiff needs to prove only a direct interference with land. The defendant must then show a lack of intention or negligence. In practice, trespass to land is restricted to intentional interference because negligent interference will normally be pleaded in the tort of negligence. It is not necessary to show that the defendant intended to do a wrongful act against the plaintiff possessor. The intention to intrude on, or interfere with, land that is, in fact, in the possession of the plaintiff is sufficient. Mistake is no defence. The old case of Basely v. Clarkson [Note 110: (1681), 3 Lev. 37, 83 E.R. 565 (C.P.).] is illustrative. The defendant was held liable in trespass to land for innocently mowing the plaintiff's grass in the belief that it was his own.

As noted above, trespass to land, like other torts of trespass, is actionable without proof of damage. Every unauthorized intrusion onto the plaintiff's land, no matter how trivial or fleeting, is actionable.

The defendant's interference with the land must be physical. There is some unevenness in the cases as to what is and what is not a physical intrusion but the requirement excludes smog, chemical fumes, smoke, noise, odour, and probably vibrations. This is another requirement that hampers the tort of trespass to land from dealing with some kinds of environmental pollution. The tort of nuisance may provide a remedy.

Trespass to land does not protect title to, or ownership of, land. It protects actual possession of land. Possession is a difficult and fluid concept of property law. It is based on the idea of occupation and control of land coupled with the intention to exclude other persons. The possessor is one who exercises exclusive occupation of land, such as an owner in occupation of his land or a tenant occupying under a lease. An owner of leased property cannot as a general rule sue in trespass because he has surrendered his possession of the land to the tenant for the term of the lease. A person who only has a licence to be on the property, such as a live-in nanny, a guest in a hotel room, and the holder of season's tickets to a seat at the theatre, does not have sufficient possession to exercise trespassory remedies. The emphasis on possession rather than ownership derives from the early function of trespass to land to minimize violence by protecting the person in actual possession of the land against forcible intrusion or eviction. So strong was that policy that even a person in wrongful possession of land has the protection of the remedies for trespass to land against all intruders other than an owner who enters on the strength of his right to immediate possession. In technical language, the defendant may not raise a jus tertii (a right in a third person) in defence to an action for trespass to land.

An owner who is out of possession but who has a right to immediate possession has a number of remedies that are loosely allied to the trespass action. First, the owner may, on the strength of his title, bring an action for the recovery of land. This was formerly known as an action of ejectment. Second, if the owner can make a peaceable entry onto the land, a request may be made of the person in wrongful possession to leave and, if there is no compliance with that request, reasonable force may be used to eject that person. Third, when a person with a right to immediate possession enters the land and takes possession, he is deemed, under the doctrine of trepass by relation, to have been in possession since the right to immediate possession arose. This allows an action for damages (known as mesne profits) to be brought for damage suffered during the period of wrongful occupation, including economic loss from the loss of use of the land, damage to, or deterioration of, the land, and the costs of regaining possession.