When the seasons change in places where deciduous trees grow.
Oaks, dogwoods, black tupelo and some maples tend to turn red, brown or russet because they produce a lot of anthocyanins.
Mar 23, Why do leaves fall off trees in autumn? The short answer is that leaves fall off trees when they aren't doing their job any more. A leaf's job is to turn sunlight into food for the tree. The simple answer is this: Leaves fall off trees so that the trees can survive the winter.
The precise timing of the color shift apparently is genetically controlled.
But the word “fall” is a bit misleading. It implies that the trees are passive this time of year, when, in fact, they are actively “pushing” the leaves off their branches.