CRIMSON MAPLE

This iteration of the common Sugar Maple (Acer saccharum) only appears in the autumn of the year. As you know, the red pigment anthocyanin ( an antioxidant which protects the leaves) is in the tree all year long. Green chlorophyll is in such great abundance at the same time that it masks the reds and yellow pigments (xanthophylls) that are already there.

Most people do not know that UV light actually destroys green chlorophyll and the leaf continually manufactures it in greater quantity than what is being destroyed by the sun so it stays green all summer.

In autumn, in order to prepare the tree for winter's dehydrating effects, an abscission layer forms across the barrier between the tree and a leaf. It's a barrier that inhibits nutrients and water from entering the leaf. Therefore, as the sun slowly destroys the chlorophyll trapped in the leaf, the other non-chlorophyll pigments present are allowed to show through. 

Also, as the above process progresses, mean nitrogen in the leaf begins to fall. When that happens sugars (glucose, fructose, sucrose and stachyose) are positively correlated with brilliant expression of color......sugar content can affect color brilliance.

My speculation is that in very wet years, the amounts of those sugars may be reduced because of dilution by water....thusly accounting for years in which fall color may not be as brilliant as in other years.....dry ones. My thoughts.

Best in Large.