Which of the following is a potential indicator of tree decay?

A potential indicator of tree decay is the presence of oozing. This phenomenon often signifies that a tree is experiencing internal health issues, which may include decay caused by fungi, bacteria, or other pathogens. Oozing can result from the sap or other internal liquids leaking out of the tree, indicating that the protective barriers of the tree have been compromised. This leakage is generally a response to stress caused by decay or infection, which diminishes the tree's structural integrity and ability to function normally.

In contrast, a nesting hole or cavity might suggest that the tree is being used by wildlife, but these features alone do not necessarily indicate internal decay. Similarly, a fruiting structure is typically a sign of fungi that could be present on both healthy and decaying trees, depending on the specific organism involved. Thus, a nesting hole, cavity, or fruiting structure may not provide a reliable indication of internal decay compared to the critical insight offered by oozing, which directly points to potential deterioration of the tree’s health.