It is one of the most beautiful times of year in State College. The cool crisp air, the holiday season approaching and the crunch of the falling leaves as you walk from class to class. But what is causing them to change and fall?

Going back to our bio classes in high school we need to know about the composition of a leaf in order to fully understand what is occurring in the leaves during the autumn. According to the USDA Forest Service, the green color of most leaves in the summer is do to the Chlorophyll in the leaves. This is arguably the most important part of the leaves because it is necessary for photosynthesis to occur and create the sugars for the trees food. But, there are also two more pigments in the leaf that are generally not seen until the autumn even though they are present in the leaf for the entire season but are masked by the green chlorophyll. Carotenoids produce the yellow, orange and brown colors in plants such as bananas, carrots and corn as well as leaves while anthocyanins are a water soluble pigment that gives plants like cranberries, apples, strawberries and leaves a vibrant red color.

 Onward State

Throughout the entire season chlorophyll is constantly being produced and used in order to maintain a healthy growing plant but as days become shorter and there is less sunlight available for photosynthesis this process slows and eventually stops all together. When this occurs the cells stop producing chlorophyll causing it to eventually all be used up and destroyed. This causes the tree to begin to seal off the connection to the leaf so that when it falls it does not create a wound to the tree. Doing this causes the glucose in the leaf to be trapped instead of circulating as it usually would. The cool nights and short days of the autumn in turn changes this glucose to more brilliant red pigments. This allows the pigment that has been hidden for the entire season to become visible as well as add more red pigment to the leaf creating the vibrant red and orange colors we come to look forward to in the fall.

As you can expect there are a lot of other factors more than just the pigments that go into the time the leaves change every year and the vibrance of the colors. According to The Forest Service as well as The National Oceanic and Atmospheric Association (NOAA) the vibrance of the leaves every year depends greatly on the weather. Exceptionally dry conditions in the late summer can cause the leaves to begin “breaking their ties” with the tree earlier than usual an cause them to fall sooner and with less intense color. Also, temperatures that are too warm or too cold can cause the leaves to fall before reaching their full potential of color. For the leaves to reach peak color they must have shorter mild days we receive in the fall and cool nights but if the temperature drops too low and reaches the frost point, the trees like most other plants, have the possibility of dying. In the trees case the tree itself will not die but the leaves will fall prematurely. 

At the time of this posting on October 22nd The Foliage Networks most recent color report shows that state college is right around the high color to peak color range on the map to the right. So get outside and try to catch a glimpse of the vibrant colors before it is all gone until next year!