When I was a young kid I thought Jack Frost was a real person, and probably good friends with Santa and the Tooth Fairy. I was told that Jack had a tremendous palate of colors that he used to paint all the intense shades of the autumn leaves. In my childhood home of east Tennessee he had a big job to do in those extensive forests. But here in coastal California, Jack’s got it made. Our native vegetation in the fall is not really that dramatic or colorful. Much of it is evergreen but even our deciduous oaks and maples just turn dull yellow and then brown. About the brightest color we get is from poison oak up in the hills and pickleweed in the salt marsh, both are a brilliant red right now. On our evening news we do not get a foliage report.
On the other hand in the cities and suburbs we often grow plants for their colorful beauty. Ginkos, sweet gums, Chinese pistachios, Virginia creeper, scarlet oaks, poplars, Japanese maples are all in glorious form right now. Some of the streets in my neighborhood are ablaze with arresting color.
So why do leaves change color before they drop? Well we all know that leaves use chlorophyll to photosynthesize. But there are two other important pigments in plants – carotenoids (which give carrots their color) and xanthophylls (the yellows). But since green chlorophyll so abundant it usually masks the other two. As sunlight decreases in the fall, plants form an abscission layer at the base of the leaf, which begins to cut of the water supply. Metabolism decreases and chlorophyll becomes less and less abundant and then those accessory pigments become visible. As the air temperature decreases sugars are more slowly removed from the leaf which boosts the production of yet more pigments called anthocyanins. These gives the red, blue and violet tints to some leaves. Eventually the leaves fall completely off and the only color left is from the tannic acid in the leaves – brown.
Whoa!! Way too complicated I thought Jack Frost was an easier answer.
This is Michael Ellis with a Perspective.