Every owner of any tree overhanging any street or right-of-way within the city shall prune the branches, so that such branches shall not obstruct the light from any street lamp or obstruct the view of any street intersection, and so that there shall be a clear space of eight feet above the surface of the sidewalk and a clearance of 12 feet over streets and alleys. Property owners are responsible for trees on their own property as well as trees on the public way that abuts their property.