Last week the fall colors were optimal here in Charleston, SC. They were the most beautiful I’ve seen here since I moved here 16 years ago. You Northerners may not know that we have such beautiful colors here. I didn’t when I lived in Ill. But we have deciduous trees and most of them change colors, except for a few like the live oak.
My question is why were they so beautiful this season? Did the frost we had two weeks ago augment the colors? I know that some colors are there all the time, masked by the chlorophyll, and when the chlorophyll disappears, they can be seen. But other colors, and the more vivid ones, are chemically produced this time of the year, by chemical reactions with the various sugars and other organic compounds. Would a frost cause the chemical reactions to produce more vivid colors? We’ve also had a drought for the last year. Would that be a factor?
The frost probably served as a trigger for the leaves to lose their chlorophyll.
The depth of the drought, the precise timing of any rain you may have had, as well as the temperature profile all contribute to the color development.
Too cold or dry -> leaves fall too soon
Too wet -> poor color development
Under normal circumstances trees also move a lot of the carbohydrates and more valuable nutrients from the leaves before they shed them. This is done by breaking down the compounds the minerals are bound up in. I imagaine a frost would rupture enough cells to prevent these compounds being removed form the leaves, as well was accelerating the speed at which the leaves are ‘shut down’. This leaves a lot of compounds in the leaves that would normally be absorbed, and these then break down into colourful pigments.