Daniel, who runs the Botany Photo of the Day blog through the University of British Columbia Botanical Garden, sez: "thought you might enjoy this pic of autumn leaf colour in vine maples with explanation as to why there is such variability."
In other words, the formation of red pigments in the autumn provides protection, preventing the too-rapid breakdown of chlorophyll which could occur in exposed (read: excess light) areas. As you can clearly see in the leaf in the upper right, the bottom-right corner has the pattern of the leaf above. Where the leaf above shaded this leaf, no red pigments were produced. Where the leaf was exposed, bright red anthocyanins were formed. To take this to a broader perspective, vine maple trees in shaded forests and under low light conditions have little need to produce red pigments, as the breakdown of chlorophyll can occur at a modest pace. However, vine maples in exposed sites turn flame orange and red, so that the pigments produced will slow the rate of chlorophyll breakdown. The leaves in this photograph are from trees that are partially exposed, hence the attractive blend of colours.scp
(Thanks, Daniel!)
