Maples along the Tamanawas Trail began their transformation as early as September. Contrary to popular belief, leaves do not change as a result of cooler temperatures. Leaves change due to a lack of light, according to sciencemadesimple.com. Green is the color of chlorophyll, the chemical trees use to transform sunlight, water and carbon dioxide into glucose, their food source. Trees need sunlight to manufacture chlorophyll. So when the sun tilts toward the southern hemisphere, trees go into a sort of hibernation during the winter, subsisting off the glucose they produced during spring and summer.