|The common misconception among most people is that the green in the leaves 'turns' yellow and orange. But the reality is that the yellow and orange were there all along. Once the leaf is cut off from the water provided by the tree the production of chlorophyll ceases. As the green chlorophyll already present in the leaf degrades the yellow xanthophyll and orange carotene that were always there will slowly start to show through.
As the process progresses there is another color that may or may not show up in the leaves. That color is red. The red is anthocyanin. Unlike the yellow and orange carotenoids that have been there all along the anthocyanin is produced after the leaf is cut off from the tree and the glucose is trapped in the leaf. It is the glucose that may eventually turn red. In order for the glucose to change to anthocyanin there must be bright sunny days and cool, but not freezing nights.
If youre viewing the colors on the Markagunt Plateau above Cedar City in Utah you may notice that there seems to be a kind of patchwork of colors in the forest. Its not your imagination. In the picture below youll notice that there are stands of Aspens that all seem to be the same color, and that next to them will be another stand with a different color. The reason for that phenomenon is because the stands are in fact clones of one tree. The trees in the stand all have the same genetic makeup, and therefore all have the same coloration.
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