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

Leaf color is a significant indicator of tree health because it can provide immediate visual cues about the physiological status of the tree. Healthy leaves typically exhibit vibrant greens due to chlorophyll, which is essential for photosynthesis and overall vitality. Variations in leaf color can signify various health issues; for example, yellowing leaves (chlorosis) may indicate nutrient deficiencies, drought stress, or diseases. Observing leaf color enables arborists to assess not only the tree's current health but also its ability to photosynthesize and grow effectively.

Bark thickness, while it can contribute to a tree's overall vigor and protection against pests or diseases, is not as immediately informative about the tree's health status as leaf color is. Root depth, although critical for stability and access to water and nutrients, isn’t as easily observed and does not provide a direct visual assessment of health from above ground. The height of the tree canopy might tell about the tree’s growth potential but again lacks the immediate diagnostic power provided by leaf color in evaluating health. Therefore, leaf color emerges as the primary characteristic for assessing tree health.