The city's tree advocates and the Kentucky Transportation Cabinet are colliding head-on over rules for safer and easier-to-maintain state roadways. The dispute comes as Louisville has identified a problem with a depleted tree canopy and has encouraged the planting of thousands of trees to combat the effects of an urban heat island. An urban heat island occurs when its warmer in a city's center compared to surrounding rural areas. The heat is exacerbated by downtown buildings, parking lots, and other surfaces like roads that absorb heat. Two years ago, research by SCaRP professor Brian Stone found that the difference between urban and rural temperatures in the Louisville area was growing at one of the fastest rates in the country. He is now studying how to reduce urban heat in Louisville.