False fall, drought

The Birch leaves are fooling us again. They're beginning to show a smattering of yellow, which, in a normal year—assuming anything is normal anymore—would be a sign that autumn is starting to make its presence known. But it's mid-August and the height of summer. There hasn't been so much as a touch of fall in the hot and humid air, so what gives? It's that D word... as in, Drought. Birch leaves are exquisitely sensitive to more than just the inevitable decline in daylength—they're not happy when the soil moisture disappears, which it most certainly is doing in these rainfall-less times. In response to drought, the leaves turn color early and fall to the ground. This is how the birches cut their potential losses, trading off the possibility of continued photosynthesis for the risk of dying from thirst. Trees can take the long view, the wait-until-next-year view well known to dendrologists and fans of the Boston Red Sox (particularly this year... alas...)