When required. Unless specifically exempted in this section, a landscape and drainage alteration permit shall be obtained from the Commissioner of Public Works prior to the commencement of any excavating, grading, regrading, landfilling, berming, diking or the installation or modification of any drainage swale, channel or pipe of any land within the Town and prior to the removal of any trees with a diameter in excess of three inches at a point 4 1/2 feet above grade.