October 28, 2022
As the days become shorter, trees (like the rest of us) prepare for winter. They begin to seal off the veins that transport nutrients to and from the leaves. Like battening down the hatch on a submarine, they cut the leaves off from the rest of the tree. If they didn’t, the moisture in the leaves would freeze and leave the tree vulnerable to injury.
The leaves have pigmented enzymes which help the tree turn sunshine into sugar - a process known as photosynthesis. The green color of leaves comes from chlorophyl, which starts to break down as the veins begin to clog, causing the green pigment to fade away.
Also in the leaves, but masked during the summer by the green, are carotenoids. These are the same enzymes that give corn its yellow coloring and make carrots orange. As the green chlorophyl breaks down in the dying leaf, the orange and gold of the carotenoids become visible.
With the warm sunny days and cool nights of autumn, trees make an over abundant supply of sugar. Anthocyanin, a reddish water-soluble pigment, is found in the leaves in response to the excessive sugar. When the tree seals the leave’s veins, some sugars and the red pigments are left behind, turning the leaves red.
The oranges and the yellows in our fall foliage display remain fairly consistent from year to year. What changes most is the amount of red. Warm sunny days followed by cool crisp nights produce lots of sugar and creates the most vibrant colors of red. If the days were cooler or the nights warmer and more humid, the colors would be more muted.
Once the veins become completely sealed, the leaves begin to drop.
The falling leaves are a critical food source for all the microbes in the soil of the forest floor - just as they are for our lawns and gardens.
Our sheep love to eat the leaves as they begin to drop, and they fight over the first few to hit the ground. They prefer the falling leaves to what’s left of their still green pasture. I wonder if they can taste the different colors. Do the gold leaves taste anything like corn? And the orange leaves, do they taste like carrots? Can they taste the sugary reds? Are some years sweeter than others? Do they compare notes with each other on the flavors of this autumn compared to last?
This past summer’s drought was so intense I worried about our trees. I thought that the leaves might all just turn brown and drop. But they didn’t. They gave us another tremendous show - and that technicolor sweetness just never gets old.