Sue Burke writes:

The U.N. Climate Change Conference in Madrid opened on Dec. 2 by calling the climate crisis a “war against nature.” But trees have always been at war, fighting for their survival. While plants may seem passive in the environment, they can sense their environments, make decisions, and respond to threats—up to a point.

Every autumn holds terrible perils for plants. While many trees drop their leaves every year, the decision of precisely when to do so is a delicate one, as Peter Wohlleben, a German forest ranger, explains in The Hidden Life of Trees. Too soon and trees lose the chance to make food for the coming spring. Too late and an early snow or ice storm can weigh down leaves, tear off branches, and cause fatal injuries.

That decision may seem automatic to a human observer, but individual trees actually make different calls, which shows how subjective the event is. Wohlleben describes 300-year-old oak trees growing side by side. One always sheds its leaves earlier than the others. “The timing of leaf drop, it seems, really is a question of character,” he writes. “The tree on the right is a bit more anxious than the others, or to put it more positively, more sensible.” The two others are “bolder,” he writes, gambling on good weather.

Trees decide when to act based on day length and temperature, which they can easily sense. Rising temperatures mean spring; falling temperatures mean fall. “And what this proves as well,” Wollenben writes, “is that trees must have a memory.” [Continue reading…]