Cool nights and chlorophyll create colorful fall season

The chemical makeup of leaves becomes especially noticeable each fall, as the vivid reds, oranges, yellows and browns burst out in an array of colorful foliage. As an area renowned for attracting leaf watchers, the colors in southern Indiana are especially important because tourism is a vital part of the southern state's economy, and the leaves contribute to that.\nAlbert Ruesink, a senior resident botanist at IU, enjoys explaining the science behind the annual leaf fireworks display that is such a boon to local tourism and pleasure to residents. As a scientist, he hears many of the misconceptions surrounding this natural phenomena.\n"One of the main misconceptions about fall is that the leaves change color from green to either brown, yellow or red," said Ruesink. "In fact, the leaves are only showing their true colors as the chlorophyll in them begins to break down."\nAs the green chlorophyll degrades there are three primary color pigments that become the dominant spectra of the leaves, Ruesink said. One color is a "lustrous brown color" characteristic of many oak trees, and the result of tannin pigments. Another is a bright yellow-orange color that comes from carotenoid pigment. Brilliant reds and purples are the result of anthocyanin pigments.\n"Another major mistaken belief is that it is temperature change that brings about the change in the leaves," Ruesink said. "In fact, it is the length of the nights that determines color conversion."\nBarring the past rainy week, the excessive dryness of this year means that many of the plants are not healthy enough to use photosynthesis, a process of changing sunlight to energy used in plants, effectively. As a result, many of the colors will not be as brilliant as in past years. To have the most colorful fall, relatively mild days with a lot of moisture are needed, Ruesnick said.\n"If you get bright sunny days and cool nights so that the sugar is not transferred too early from the leaf, that is when the colors are really outstanding," Ruesink said. \nWhile southern Indiana as a whole is known for its forests and rolling hills, Bloomington enjoys particular fame during the fall because of the city and campus planners. On campus, for every tree cut down two additional saplings must be planted, and the trees have also been selected on the basis of their fall color schemes.\n"The planners opted to plant trees that have particularly bright changes, such as the Georgiana Maples on Seventh Street," explained Ruesink. "So when you are walking around campus, look around and appreciate the science and beauty behind nature's marvels."\nLocal color is especially important to nearby Nashville, Ind., which receives the majority of its 3.5 million annual tourists during the fall season, said Kate Mejaski of the Brown County Convention Center.\n"During September and October, Nashville averages about $13 to $16 million in monthly revenue, which is the majority of the yearly totals, so the fall season is vitally important to our economy," Mejaski said.\nBeyond the economic benefits that the leaves engender, they also make the stressful time of midterms and the fall semester more pleasant to the student population at IU.\n"The leaves are gorgeous this time of year," said senior Kristi Love. "They are the best part about living in Indiana."\nThis sentiment is echoed by senior Frank Alexander.\n"We have a dryer climate in Colorado where I am from, and while there are numerous Pines and Aspens you don't get the same variety of trees that makes Bloomington such a beautiful to go to school in the fall," he said.\n-- Contact staff writer Scott Shackelford at jschacke@indiana.edu.