If you were like me as a kid, you spent this time of the year after school running in and throwing up tons of red, yellow and orange leaves in your backyard or neighbourhood park….It was a time of great happiness as the steady downpour that came off the trees found their way to the ground where some adult piled and stuffed garbage bag after garbage bag of crinkling (or sometimes soggy) leaves and twigs.
While how we treat the fallen leaves has changed (I mow them with my mulcher-mower and return the nutrients to earth) the vibrancy of the reds of the maples, the yellows of the poplars and the oranges of the hickories really has not. What a beautiful kaleidoscope before the dullness of the late Fall gives way to the white blanket of a cold, beautiful Canadian winter….
Yet how many of us stop to wonder exactly how these leaves turn these wild shades? What is the mechanism that makes this happen? And how come these colours aren’t seen any other time? Well, the answer is relatively easy and yet also complex (much like nature itself).
Who would have guessed that all those wild colours are present in the leaves themselves all year but are simply overpowered by the omnipresent GREEN produced by the chlorophyll of the leaves? Here we go back to Grade 12 Biology for a brief flash…trees actually don’t eat food like animals…they actually manufacture it themselves. Or as the Church Lady would say, “How Convenient”….That’s right the chlorophyll pigment which is produced as a result of photosynthesis (CO2 + water + nutrients = O2 + carbohydrates (sugars)). The sugars keep the tree growing and are also sent to the roots to be stored to initiate photosynthesis the following Spring.
As the days get shorter (and cooler) the tree senses this and cork cells develop, blocking the uptake of water and nutrients by the leaf so that it slowly dies and abscises (sorry, falls off). But before it falls, the chlorophyll dies showing the brilliance of the gold or yellow or orange beneath. The yellow pigment is given a fancy name – xanophylls while the orange hues are called beta-carotenes. The red pigments (called anthocyanins) that we find in the oaks and maples is much more interesting. They are manufactured in situ as the leaf is dying and half the chlorophyll has died….Very interesting.
Some feel that the anthocyanins have allelopathic qualities – that is they act as a natural herbicide, preventing the growth of some trees this providing a competitive advantage to maples and oaks in the forest…..Again, how convenient!
Then there’s global warming –although the tree depends principally on shorter days to figure out when to shut down, the warmer temperatures seem to be pushing the date later and later…Who knows – maybe one day we will be playing in those piles of leaves while we celebrate the Winter Solstice….I hope not! Have a great, wonderful Fall!
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