Can trees predict the weather?

“Oak before ash, we’ll have only a splash. Ash before oak, we’re in for a soak.” This saying claims that if oak trees come into leaf in spring before ash trees, then there will be less rain in the summer. Oak and ash trees do come into leaf at different times, because leaf growth in oaks is triggered by temperature, whereas ash trees use longer days as their signal. But there’s no evidence that a warmer spring results in less rain that summer. Pine trees do close their cones in humid weather, though, which can indicate that rain is on its way.