The Director of Public Properties shall have the right to plant, trim, preserve and remove all trees within the lines of all streets, alleys, avenues, lands, lanes, squares and public grounds as may be necessary to insure safety, or to preserve the symmetry and beauty of such public grounds. The Director, under the power given herein, may cause any tree which is in an unsafe condition, or which by reason of its nature is injurious to sewers or other improvements, or is affected by any injurious scale or other pest, to be removed.