It is that time of year. As the other pigments are drawn back into the plant, the red, orange and yellows of the anthocyanin compounds remain.
The leaves of the dogwood (Cornus sanguinea) were once as green as the oaks.
The intriguing thing from a natural navigation perspective is how this effect doesn't happen uniformly across the plant.
We should expect differences between species, they each come into leaf and drop them according to their own phenological schedule. But differences within the same plant points to something more interesting.
If you look at the image below you'll see some very green leaves from the same dogwood plant (and even within the same leaf). The more exposed leaves seem to display this effect earlier and more dramatically.
There also appears to be a correlation with exposure to the sun, and therefore direction.
This is certainly true in summer and well before autumn in the 'copper' species (see this page for more).
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