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

Excessive pruning negatively affects a tree's health primarily by causing stress and making it more vulnerable to pests and diseases. Trees rely on their leaves to photosynthesize and produce energy. When too much foliage is removed, it can severely reduce the tree's ability to gather sunlight and may lead to a decline in overall vigor.

Pruning also leaves open wounds on the tree, which can serve as entry points for pathogens and insects. These wounds take time to heal, and during this period, the tree may be more susceptible to infections and infestations. Additionally, the stress from losing a significant portion of the tree's leaf area can compromise its immune system, making it harder for the tree to fight off diseases and recover from any infestations.

The other options do not accurately reflect the consequences of excessive pruning. Stronger root development is more likely to occur when a tree is healthy and adequately pruned, not excessively pruned. While new growth may initially occur after pruning, excessive removal of branches can lead to weak, poorly structured growth that can further harm the tree in the long run. Healthier foliage is unlikely to result from excessive pruning, as the tree's overall health can deteriorate due to such stress.