ISA Certified Arborist Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

When trees experience drought conditions, one of their primary physiological responses is to close their stomata, the tiny openings on the leaves responsible for gas exchange. This closure is a crucial adaptation to conserve water. By reducing water loss through transpiration, trees can maintain their internal water balance even when external moisture is limited.

Stomatal closure is part of a broader set of strategies trees employ to cope with limited water availability. While leaf drop is a common response as well, it often comes into play in more extreme situations or prolonged droughts after the initial protective mechanisms, such as stomatal closure, are no longer sufficient. Root expansion can occur, but it typically happens when water is available in deeper soil layers and is not a primary response during acute drought. Increased photosynthesis is also unlikely during drought because the closure of stomata limits the intake of carbon dioxide necessary for this process; hence, photosynthesis might be reduced rather than increased.

Overall, the response of stomatal closure is significant because it effectively seeks to minimize water loss and sustain the tree's life functions during challenging environmental conditions.