ISA Certified Arborist Practice Exam 2025 - Free ISA Arborist Practice Questions and Study Guide

The symptoms of wilting leaves, early leaf drop, and discoloration are clear indicators of tree stress. Trees experience stress due to various environmental factors such as drought, nutrient deficiencies, pest infestations, or disease. Wilting leaves suggest that the tree is unable to maintain adequate water levels, often due to root damage or insufficient soil moisture. Early leaf drop can be a response to environmental stressors, as the tree sheds leaves to conserve resources. Discoloration, particularly yellowing or browning of leaves, can signal nutrient deficiencies or issues such as root rot, further suggesting that the tree is not in optimal health.

In contrast, the other options describe conditions that are characteristic of healthy, thriving trees. Green leaves and vigorous growth indicate a well-nourished tree; rapid growth and thick bark suggest strong vitality and resilience; high fruit production and bright foliage are also signs of robust health. These traits do not align with the symptoms typically associated with tree stress. Therefore, option B stands out as the most accurate representation of what stressed trees exhibit.