Which characteristic may NOT be essential for assessing a tree's overall health?

Tree height is not considered an essential characteristic for assessing a tree's overall health because it does not directly indicate the physiological condition or structural stability of the tree. While tree height can provide context about the species and age of the tree, it does not assess how well the tree is functioning or if it is experiencing health issues.

In contrast, growth habit is crucial as it reflects the tree's adaptability and how it responds to environmental stresses. Leaf color is an important indicator of a tree's health, signaling nutrient deficiencies, water stress, or disease. Root system health is vital since it underpins the tree's stability, nutrient and water uptake, and overall vitality. Thus, focusing on these aspects provides a more comprehensive understanding of a tree's health status compared to simply considering its height.