Why Leaves Change Colors In The Fall
Jack Frost is not to blame for the yellow blanket of trees that color our valley. Chemical changes within the individual leaf are what creates the beautiful fall change.
Most of the food sources necessary for a tree's growth are manufactured within each leaf. The cells that help produce this food contain chlorophyll, which is what gives the leaf its green color. Leaves also contain a yellow and orange pigment, but they are masked by the higher amount of chlorophyll. In the fall, when the trees stop or slow down their food-making process due to temperature and sunlight changes, the yellow colors become more visible. Less chlorophyll = less green.
Trees with higher exposure to the sun during the day, with chilly night temperatures, are more likely to turn red. This is because the chlorophyll creates sugar for the tree, but the cool nights (temperatures below 45) stops the sugar from moving out of the leaf. This is why the colors can vary from tree to tree, depending on where the sunlight hits each one. Weather conditions will also vary from year to year, creating unique fall looks each year.