A vegetated streamside management zone shall be maintained or established adjacent to streams, ponds, lakes and marshes, except that no streamside management zone shall be required when Atlantic White Cedar is proposed to be harvested, established, restored or regenerated. The streamside management zone shall be at least 25 feet in width. Where soils are severely erodible, slopes exceed 10% or streamside vegetation is not vigorous, the streamside management zone shall be increased up to a maximum of 70 feet to buffer the water body from adjacent forestry activities;