The first day of fall began on September 23rd at 5:05 a.m. in the Northern hemisphere, suggests The Old Farmer’s Almanac. For those of you who live in the northeastern United States, you can certainly tell that fall time is here. At St. Bonaventure University we are surrounded by mountains and trees galore. For me, this is my favorite time of year to be on campus and look at the foliage in the scenery.

Devereux Hall at St. Bonaventure University.

But, what causes the leaves to change color? The SUNY College of Environmental Science and Forestry website provides us with some simple explanations shown below.

Green Leaves in the Spring and Summer. In leaves’ cells there is a chemical called chlorophyll, which makes leaves green. Chlorophyll absorbs energy from the sunlight and is used to transform carbon dioxide and water to carbohydrates.

Fall causes the Chlorophyll to Break Down. Because of the change in sunlight and temperature, leaves are unable to continue their food-making process, making the green color turn into colors of yellow to orange.  However, other colors are formed if other chemical changes occur, such as mixtures of red, purple and brown. Some trees show many colors while others only one color such as oak trees that mostly show brown. The variety of colors is due to random mixing of chlorophyll residue and other pigments in the leaf during the fall.

Why do Leaves fall from the Tree? Where the stem of the leaf is connected to the tree, the layer of cells that develops eventually begins to detach from the tissues that support the leaf. A tree “seals the cut” so when a leaf has fallen off the tree or blows away, it leaves behind “a leaf scar.”

Some leaves do not fall. Some leaves stay on a tree until growth starts again in the spring, like the dead brown leaves from the oaks. Down South is where you can find broad-leaved trees are evergreen, which means the leaves keep their green color even in the mild winters. Most conifer trees (pines, spruces, firs, etc.) are evergreen in the North and the South. Because of their constant green needle-like leaves, it is easy for them to me around all year; while individual leaves can stay on for two to four years.

Weather Affects Color Intensity. Temperature, light, and water supply impact fall leaves’ degree and duration of color. The best time to sit outside and enjoy the fall colors would be on a clear, dry and cool day.

This slideshow requires JavaScript.

Do you have any fall pictures to share? What do you like most about fall? Feel free to share your stories and photos!