It seems fitting to talk about color this month. While spring is aglow with verdant greens and winter features brilliant white snow, no season can equal the cornucopia of color that fall brings.
Take a stroll along the many hiking trails in the Hastings area this month and you will notice the tops of trees turning yellow or orange. In one case on Pine Street just the east side of a tree has turned vibrant orange-yellow. We all know that leaves change color at this time of year but what is really going on?
During the summer trees use their leaves as food production sites. The leaves take in carbon dioxide and sunlight. Add a little water which is brought up from the ground by the tree roots and voilÃ -the tree creates a sugar called glucose. Glucose is the food the tree uses to grow. This process is called Photosynthesis (from the Greek word photo which means “light,” and synthesis from the Greek work syntithenai, which means “to put together”) and it uses a pigment called chlorophyll to help absorb the sunlight. Chlorophyll is what gives leaves their green color.Â Chlorophyll is not a very stable substance and sunlight actually causes it to breakdown. During the summer trees continuously create chlorophyll to replace that which is breaking down. Plants need lots of sunlight and warm temperatures to make chlorophyll.
Trees also have another pigment in their leaves called Carotene (think orange-yellow colors like carrots). This pigment supplements chlorophyll by absorbing other wavelengths of sunlight. This pigment is more stable than chlorophyll and doesnâ€™t break down as easily in sunlight.
During the winter the delicate tree leaves would not survive. Besides, there wouldnâ€™t be enough light and warmth to continuously create chlorophyll all winter. In the fall the longer, cooler nights and the shorter days signal the trees to slow down chlorophyll production. As the remaining chlorophyll in the leaf breaks down the green pigment disappears, leaving the more stable yellows color of the carotenes.
But what about those awesome reds that really make fall gorgeous?
The red colors of fall are more variable year to year and they come from a third group of pigments called anthocyanins. Anthocyanins also absorb light, but they are dissolved in sap in the leaves. During the summer the tree allows glucose and water to flow freely in and out of the leaf to nourish the whole tree. When fall begins the trees produces a corky substance at the joint where the leaf connects to the tree. This corky substance inhibits nutrients from flowing in and out of the leaf. Glucose in the leaf becomes trapped. When the sugars in the leaf reach a high concentration they react and form anthocyanins which result in the brilliant red fall colors of our sumac, red oak and red maple. The temperature and moisture level of the environment influences how brilliant our fall colors are. The cool temperatures stop the chlorophyll production. If the temperature stays above freezing it helps the formation of anthocyanins. Dry weather also helps the anthocyanin production. The best weather for lots of reds in the fall foliage are long, cool, but not freezing nights and dry sunny days.
When corky barrier between the leaf and the twig is complete the leaf is ready to fall to the ground. Once on the ground it will replenish the nutrients in the soil, and provide food for many micro-organism. It is amazing to consider how much our entire planet depends on this process. Almost every living thing relies indirectly or directly on plants for a food source. Â Â Sunlight + water + CO2+green plants=Oxygen + sugar
So this fall when your toddler or grandchild leaps into a pile of leaves with a giggle-stop for a second to consider the fascinating puzzles and magical connections we find in natureâ€¦and then jump right in with them!
A few other terrific opportunities to get out and enjoy nature in the next few weeks include the Fall Raptor Release on September 25th and the St. Croix Valley Apple Fest in October.
Until next time, I hope to see you on the trails.