Wis. Stat. § 893.30
In every action to recover or for the possession of real property, and in every defense based on legal title, the person establishing a legal title to the premises is presumed to have been in possession of the premises within the time required by law, and the occupation of such premises by another person shall be deemed to have been under and in subordination to the legal title unless it appears that such premises have been held and possessed adversely to the legal title for 7 years under s. 893.27 , 10 years under s. 893.26 or 20 years under s. 893.25 , before the commencement of the action.
Wis. Stat. § 893.30
The lowest burden of proof applies in adverse possession cases. Kruse v. Horlamus Industries, 130 Wis. 2d 357, 387 N.W.2d 64 (1986).