1. When any lands have been so classified the classifications shall be continued as long as proper forest conditions and practices are maintained and continued thereon, and for such periods of time as do not exceed the provisions of this chapter.

2. Use of such lands for pastures, destruction of tree-growth and failure of owner to restore forest conditions, removal of tree-growth and use of land for other purposes, or any changed condition which in the opinion of the commission shall show that the requirements of this chapter are not being fulfilled, or the use of such lands for pasture in violation of any regulations promulgated by the commission shall be sufficient ground for the cancellation of such classification. If the commission find the provisions of this chapter are not being complied with, it shall forthwith cancel the classification of such lands, sending notice of such cancellation to the assessor, the county clerk of the county in which the land is situated and to the owner of such lands. Such lands shall thereafter be taxed as other lands.