ISA Certified Arborist Practice Exam

How does temperature influence tree leaf drop in deciduous trees?

1. Cold temperatures promote leaf growth

2. Warm temperatures inhibit leaf drop

3. Cold temperatures signal trees to enter dormancy

4. Temperature has no effect on leaf drop

The correct answer is: Cold temperatures signal trees to enter dormancy

The correct response highlights the critical role that cold temperatures play in the life cycle of deciduous trees. As temperatures decrease, they trigger physiological changes in the trees, signaling them to prepare for dormancy. This process involves the breakdown of chlorophyll in the leaves, leading to the vibrant autumn colors we see before leaf drop. During this transition, trees also begin to form an abscission layer at the base of the leaf stalk. This layer is essential for the separation of the leaf from the tree, ultimately causing the leaf to fall. The approach of cold weather acts as a natural indicator that trees need to conserve energy and reduce water loss, making it a crucial factor in the timing of leaf drop. Understanding that warm temperatures can lead to extension of the growing season and leaf retention, as well as the fact that temperature fluctuations can influence metabolic processes within the plant is important, but these aspects reinforce the primary influence of cold on initiating dormancy and leaf shed. Hence, the answer appropriately encapsulates how temperature influences this vital seasonal change in deciduous trees.