10.29/09 EXPLAINING THE INEXPLICABLE

MOST RED OAKS ARE BROWN OR BRONZE THIS FALL
SOME RED OAKS ARE A DEEPER BRONZE
ONLY A FEW RED OAKS ARE TRULY RED THIS FALL

8:00 AM. 48 degrees, wind SW, light to moderate. The channel is crawling slightly, the sky is overcast and the barometer predicts partly cloudy skies.
I have been watching the coloration or our red oaks (Quercus rubra) and it looks like most will simply turn brown or bronze this year rather than the usual blood red. There are a few red colored oaks but they are mostly saplings. The hillsides are now mostly brown or bronze with oaks, except for a few maples and poplars with leaves, and of course the evergreens. It is still pretty but quite muted.
The fall color of our deciduous trees is determined by a number of complex factors, the foremost being shortening day length, which triggers the growth of a corky layer of cells (the abscission layer) at the base of the leaf petioles, which cuts off the flow of water and nutrients to the leaves. This causes the green chlorophyll cells to die, unmasking the other pigments of the leaf. It also makes the leaves ready to fall from the tree. The best color seasons are those in which there is a succession of cold but not quite freezing nights, and fall soil moisture also is a factor. Once the abscission layer is formed the leaves can be brought down by snow or high winds and rain, in the absence of which the leaves will hang on longer. A killing frost while leaves are still green can spoil the fall color. Each tree and shrub species has its own genetically determined leaf pigments, and even individual trees have their own genetic variations. The later fact leads to the horticultural selection of individuals for their leaf coloration and consistency, which are then propagated asexually. All in all, fall leaf color is a complex and poorly understood natural process, but none-the-less an annual event of amazing beauty. I feel as though I have just tried to explain the inexplicable. We will still have several weeks of changing and gradually diminishing fall color, until the woods are again bare.