Remove from the property all dead trees, and maintain all weeds and other vegetation at a height of no more than three inches, except as otherwise provided therein, if such weeds or other vegetation are within 100 feet of a building or structure located on such property or on adjacent property. This requirement does not apply to the maintenance of trees, ornamental shrubbery or plants which are used as ground cover provided such do not provide a ready fuel supply to augment the spread or intensity of a fire; nor does it apply to a native shrub, provided such shrub is trimmed up from the ground to 1/3 of its height; does not exceed 216 cubic feet in volume; is spaced at a distance of not less than three times its maximum diameter, but not less than 18 feet from the edge of any other native shrub, building or structure; and all dead wood and other combustible material within 18 feet of such shrub is removed except as provided above.