ISA Certified Arborist Practice Exam 2025 – All-in-One Resource for Comprehensive Exam Success!

Trees play a vital ecological role in forests through various functions that support both the environment and other living organisms. Providing habitat is fundamental, as trees offer shelter and nesting sites for numerous species. They also contribute significantly to nutrient cycling, as through processes like leaf litter decomposition, trees help return nutrients to the soil, which in turn supports other plant life.

Moreover, trees influence water cycles and stabilize soil, meaning they help regulate water retention in ecosystems and prevent erosion by anchoring soil with their root systems.

The option referring to increasing atmospheric CO2 levels does not align with the beneficial roles trees play. Instead, trees are known for sequestering carbon dioxide from the atmosphere through photosynthesis, thus helping to mitigate climate change rather than contributing to increased CO2 levels. Their role in reducing atmospheric CO2 levels is crucial for maintaining ecological balance, making this the correct choice for what is NOT an ecological role of trees in a forest.