Improvement consisting in the protection and maintenance of trees and plants not sown or planted by tenants and of trees and plants spontaneously grown prior to tenancy.

When the improvement consists in the protection and maintenance of timber or fruit trees or of other useful trees or plants not sown or planted by any of the persons mentioned in section 3, or of such trees or plants spontaneously grown prior to the commencement of the tenancy, the compensation to be awarded shall be the proper cost of such protection and maintenance ascertained as provided in section 11.