Gambel Oak Leaf in Fall
When fall comes the oak tree grows a tissue layer (Abscission layer) across the base of each leaf that cuts off the flow of nutrients to the leaf. Chlorophyll, which is what gives leaves their green color, is quickly broken down by the sun. That exposes the red pigments in the leaves which are normally hidden. These pigments too are degraded by the sun and the leaves eventually turn brown.
They sure are pretty for a while. Especially, in New Mexico, USA where we don’t see much red color in the fall. Nothing like the maple trees that grow in the eastern USA.
