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

The presence of mushrooms growing at the base of a tree is a strong indicator of a fungal infection. Fungi often thrive in decaying wood or weakened tissues, and the appearance of mushrooms, which are the fruiting bodies of the fungi, suggests that there is internal decay occurring within the tree. This can be due to a variety of factors including root rot or heart rot, which may not be immediately visible without further inspection.

Mushrooms can emerge from both live and dead trees, but their presence often signifies that the tree is compromised in health. They can also provide clues about the type of fungus present, which can help in diagnosing the specific issues affecting the tree. Understanding the relationship between mushrooms and fungal infections is crucial for tree care, as identifying and managing these infections early can help prolong the life of the tree.

The other options may not specifically indicate a fungal infection. Yellowing leaves can be a sign of various issues, including nutrient deficiencies or environmental stress, while peeled bark might suggest mechanical injury or environmental factors rather than a fungal presence. Falling branches can indicate structural issues but not specifically confirm fungal infections without additional symptoms. Thus, the growth of mushrooms at the base is the most definitive sign of a fungal infection in the context provided.