Fall colors, but not all of the trees have turned yellow, yet...

The nights grow longer, the temperature continues to drop, yet the trees at #fossilatmospheres cling to their leaves. They are all beginning to turn yellow, though some of them seem as green as the day they set leaves this spring! Several of the greenest are control trees, so the stress of elevated conditions takes its toll. However, one of the greenest is at 1000 ppm. Go figure... @FossilAt @smithsoniannmnh @smithsonianenvironment