ISA Certified Arborist Practice Exam 2025 – All-in-One Resource for Comprehensive Exam Success!

Defoliation refers to the loss of leaves from a tree, which can occur due to various reasons including pests, diseases, environmental stress, or seasonal changes. When trees lose their leaves, they experience a reduction in their ability to photosynthesize, which is the process by which they convert sunlight into energy needed for growth and health.

The loss of leaves can significantly hinder a tree's overall health, as it affects its energy reserves and limits its ability to produce the sugars necessary for vital functions. Additionally, defoliation can make trees more susceptible to other stressors, including drought or disease, further complicating their recovery. In situations where a tree undergoes substantial or repeated defoliation, it may weaken its structural integrity and lead to longer-term health issues.

The other options do not align with the biological and physiological impacts of defoliation on trees. Trees do not generally improve in growth following defoliation, nor do they experience an increase in fruit production as a result. Furthermore, defoliation clearly affects trees, rather than having no effect at all. Thus, the impact of defoliation aligns with the understanding that it hinders tree health and recovery.