This maple leaf is red due to the presence of anthocyanin, a pigment that can also create purple colors in leaves
This maple leaf is red due to the presence of anthocyanin, a pigment that can also create purple colors in leaves
Montgomery County is closing in on peak fall color – that time of year where the majority of deciduous trees are displaying their most vibrant colors. We are just a bit behind schedule from our average peak color time, which tends to fall in mid-October. But how fun that we get to enjoy near-peak color during Halloween and early November!
The factors that drive color change in trees include the length of our days, daytime and nighttime temperatures, and autumn rainfall. Color change occurs in trees when they sense the right combination of factors, like shorter days and cooler nighttime temperatures. Those two factors in particular signal to the tree that winter is coming and that it is time to turn off photosynthesis for the year.
Usually we see green leaves on trees because they are chock full of chlorophyll, the molecule that drives the process of photosynthesis. Photosynthesis is the way plants make food from sunlight and carbon dioxide. Chlorophyll molecules don’t last forever, however, so trees must manufacture chlorophyll throughout the year to keep the photosynthetic factory working at full tilt. When fall weather starts to roll in, trees begin going dormant by halting production of the chlorophyll molecule. Since no more chlorophyll is made, the chlorophyll still present in tree leaves breaks down and leaves only pigments behind, which gives us our brilliant fall foliage. Eventually, trees shed the leaves entirely. In order to shed them safely, without opening up any wounds on the tree that would expose the bark to disease, a process called abscission takes place. Trees form a layer of special cells at the base of each leaf stem, or petiole. When this layer is fully formed, leaves fall away from the tree leaving a small scar behind. This is the leaf scar, which is distinctive from tree to tree. Leaf scars are one of the most important characteristics used to identify trees in the winter.
Before we make it to winter, however, we have a lot of colorful foliage to enjoy! Weather plays a role in whether fall foliage looks beautiful or turns prematurely brown and crunchy. Here’s what a few different situations can do to fall leaf colors:
• Early frost – if we get an early frost, cold temperatures can cause still-green leaf tissue to die. This will turn leaves brown and crunch around the edges.
• Dry conditions – if we have too little rainfall during autumn, tree colors will be less vibrant.
• Summer drought – if we have too little rainfall during summer (think the drought of 2012), almost no fall color will show through. Trees may lose their leaves prematurely during drought years.
• Cold, but not freezing, overnight lows – Overnight lows near freezing produce physiological changes that make more pigment accumulate in leaves, resulting in brighter colors.
Now that we know how leaf color appears and what can make it the most vibrant, why do different kinds of trees have different leaf colors? The simple answer is that each tree species has a distinctive combination of pigments. Anthocyanins cause purples and reds, carotenoids cause oranges and yellows, and the mixture of the two (plus broken down chlorophyll molecules) can cause a very wide variety of beautiful colors.
This weekend is the perfect time to plan a trip to Shades or to take a walk through Sugar Creek Nature Park. Other beautiful views can be found at the Lane Place Arboretum, Bachner Nature Reserve, and throughout Wabash College’s campus. Take a few moments to enjoy this brief but brilliant foliar show!
Ashley Adair is the Extension Educator for Agriculture & Natural Resources at Purdue Extension – Montgomery County. She can be reached at (765)-364-6363 or holmes9@purdue.edu.