(1) The department shall assess land as forest lands according to the following basic determinations.

(a) Forest lands are:

(i) contiguous land of 15 acres or more in the same ownership that is capable of producing timber that can be harvested in commercial quantity;

(ii) land that is producing timber or land in which the trees have been removed by man through harvest, including clear-cuts, or by natural disaster, including, but not limited to fire;

(iii) land that is not classified as nonforest land. Nonforest land is used for agricultural, nonqualifying agricultural, industrial, commercial, or residential purposes.