Every autumn, millions of deciduous trees undergo a noticeable transformation: their leaves change color and then fall, preparing the tree to face the harshness of winter.
But how do these trees "know" that it's time to start this seasonal transition? This phenomenon is actually a clever mix of environmental cues and internal biological processes.
Illustration image Pexels The key factors
Trees primarily respond to two natural factors to trigger leaf fall: the length of the day and the drop in temperatures.
The duration of daylight, also called photoperiod, is one of the key triggers for leaf shedding. As autumn progresses, the days grow shorter, sending a signal to trees that winter is approaching.
Trees have specialized light-sensitive receptors that measure daily exposure. When the days get shorter, these receptors send a chemical message to the rest of the tree, informing it that it's time to begin preparing for dormancy.
Once the tree "understands" that winter is near, it starts producing specific hormones, mainly abscisic acid.
This hormone signals leaf cells to form a layer called the "separation layer" at the base of the petioles (the small stalk attaching the leaf to the tree). This layer gradually cuts off the supply of water and nutrients to the leaf, causing the color change and, eventually, the leaf's fall.
But why?
One reason trees lose their leaves is to conserve resources during the winter. When temperatures drop and water becomes less available in liquid form, it becomes more difficult for trees to maintain their leaves, which require a lot of energy to sustain.
By shedding these "energy consumers," the tree can focus its resources on protecting its roots, trunk, and branches.
Finally, losing leaves helps the tree survive winter conditions. Without leaves, there is less surface area exposed to cold winds and snowstorms. Trees are better protected from the risks of breakage or water loss.