When Trees Wake Up

By Jennifer Hunt, Content Writer

As spring approaches, new life emerges all around us. Certain bird species begin mating and pairing rituals, perennial plants poke up out of the soil, and trees begin the complicated process of exiting dormancy. Read on to learn about a tree’s waking moments through light changes and hormonal responses.

Phytochromes (just under the tree’s bark) are activated by the increased red light associated with longer periods of sunlight. Rising temperatures, with regular periods above freezing in the spring, signal the tree to resume growth. Abscidic acid (ABA), which slows daily processes in the dormancy phase, lets go of the reins, and auxin (a plant hormone responsible for growth and development) takes over. Ethylene, another plant hormone that helps facilitate leaf detachment during dormancy, takes on another role by aiding bud breakage and rehydration in the tree. Although it once prevented water and nutrients from traveling through the entire tree, ethylene now facilitates rehydration. Ethylene influences stem elongation, can modify growth patterns, and works in balance with auxins to regulate stem and root growth.

Much of this process is invisible to the human eye, but our first clue that a tree has awakened is bud swell. Buds that formed in the summer or fall begin rehydrating and swell, which leads to bud break, the period when the buds fully open and new leaves or flowers emerge. Tiny leaves begin to unfold and expand, allowing the tree to start photosynthesis again. As the tree absorbs more sunlight, it produces more energy, fueling further growth of leaves, shoots, and flowers. Interestingly, some species, like red maple and aspen, break dormancy early, while others, like oaks and walnuts, take their time. This staggered timing helps minimize competition and protects against unpredictable spring frosts.

The awakening of certain trees provides humans with tasty opportunities as well. The warming temperatures cause sap in maple trees (a mixture of water, sugars, and nutrients) to start flowing again. This movement happens due to temperature fluctuations: freezing nights and warmer days create pressure changes within the tree, pushing sap upward. Humans exploit this daily movement by ‘tapping’ sugar maple trees, the beginning of the process of making maple syrup. While much of the visible activity happens in the branches, roots also become more active in the spring. They begin absorbing more water and nutrients from the soil, supporting the new above-ground growth. As spring progresses, trees fully leaf out, flowers bloom, and the growing season is in full swing. The tree now focuses on energy production, developing fruit (if applicable), and preparing for the next seasonal cycle.

As trees awaken from dormancy, they embark on a remarkable transition fueled by light, temperature changes, and hormonal shifts. From the swelling of buds to the unfurling of leaves, this process marks the beginning of a new growing season. While much of this transformation happens out of our sight, its effects shape the landscape around us, providing shade, oxygen, and even the sweet reward of maple syrup. As spring progresses, trees continue their journey of growth and renewal, reminding us of nature’s resilience and the cycle that sustains life.

Want to learn more about tree cycles? Read our companion piece about trees entering dormancy, Let Sleeping Trees Lie