Shedding that stale air

Can trees be recognized by the sound made by their leaves? For poplars, the answer is "yes". Their flat petioles anchor the leaves in a more flexible position, and are sensitive to the slightest breeze. This unusual adaptation is not meant to make the leaves "sing", however, but to allow them to move more easily.

When they move, leaves rid themselves of some of the layer of air that clings to them. This thin film of stagnant air surrounding the leaf, the boundary layer, interferes with photosynthesis by reducing gas exchange between the leaf and the air around it. So for a poplar, a thinner boundary layer improves the process of photosynthesis.