- Author: Robert J Keiffer
We all have experienced the lovely red, orange, and yellow colors of autumn oak leaves and most of us look forward to this annual reminder of the fall season. Leaf colors basically come from four pigments that are naturally produced by leaf cells .... chlorophyll (green), carotenoid & xanthophyll (yellow,orange, and brown), and anthocyanin (red). Environmental factors influence the amounts of each pigment in the leaf and can therefore alter leaf color.
Chorophyll, which is usually present in large quantities and reflects green light, can diminish during periods of less sunlight, lower temperatures, higher sugar levels in the plant, and changes in water availability. When this occurs, the chorophyll no longer can "mask" the lesser amounts of the other pigments. One of these... anthocyanin, is a water-soluble pigment that occurs in cell sap, the molecules reflecting the red wavelengths of light (thus showing red color tot he human eye).
Occasionally at the UC Hopland Research & Extension Center in southeast Mendocino County, we find oak seedlings during the springtime that portray these red leaf colors. These seedlings are usually in areas of fairly high shade and tree canopy coverage. This photo of a young Black Oak (Quercus kelloggi) seedling was taken on May 7th.