My tree got leaves really early this year. The trees started flowering and budding in late Februrary. So, my maple tree is running out of chlorophyll and starting to change colors even though it is still summer. I used to think that the leaves changed after the first frost, but our coldest temp was last weekend at 65 degrees, well above frost temps. In areas with long growing seasons, like here in the Southern U.S., some trees will run out of chlorophyll long before autum actually arrives. In fact, we are just starting into hurricane season here. Autumn usually doesn't arrive until after hurricane season.
