Senescence: The Change of Autumn

By Timothy J. Palla, NJSOC AmeriCorps Member

The chill is back in the air. We all know that means the end of summer and the beginning of our most colorful season, autumn. This season brings us one of the most glorious transformations in nature. The leaves change color and this transition is called senescence which is a natural process trees go through when dropping their leaves. As trees prepare to drop their leaves they change color due to natural chemical reactions.

Here in the northeast we have several tree varieties that change color as autumn approaches. Many of these trees have colors specific to them as in; Oaks turn red, brown or russet; Yellow-poplar, golden yellow; Beeches turn light tan and so on. Species of trees can have slight variations like the maple: Sugar maple, orange-red and red maples turn bright scarlet. So your own backyard may become a beautiful mixed display of these variant colors.

The only trees that go through senescence are broad-leaf deciduous trees. They go through this change for defense since their leaves are not protected from the damage that freezing can do. The change is triggered by many factors like temperature, rainfall and food supply. The most important and unvarying factor is the length of days and the increase in nighttime. As night increases the plants stop producing chlorophyll which allows two other chemicals to show their colors, carotenoids and anthocyanins. Carotenoids produce the yellow, orange and brown colors seen in leaves and anthocyanins produce the variable red colors. The different balance of these two chemicals is what gives each tree its unique fall color.

The fall change begins in New England around September and moves south to Connecticut in October. This small window of change adds to the popularity of seeing the leaves change. “Leaf-peeper”, is the term used for people who travel from all over the world to experience this incredible transition. It is a time where everyone can revel in the beauty of nature.

So, rather than running away from autumn nipping at our heels this year, we should embrace the change and watch this event unfold as it has for thousands of years. Since every year can be different than the one before take pride in seeing something that has never been seen before.