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

Soil compaction refers to the process where soil particles are pressed together, leading to decreased void spaces or pore spaces within the soil. This phenomenon directly affects the soil's ability to hold water and air, which are vital for tree health. When soil is compacted, the reduction in pore space limits the amount of air that can reach the roots, which is crucial for respiration.

Additionally, less pore space means that water is less easily retained and may not percolate through the soil as effectively. This results in reduced water availability for tree roots, which can lead to stress, hindered growth, and even decline in tree health over time. Trees rely on the soil not only for nutrients but also for adequate moisture and air, making compaction a significant factor in tree care and management.

The other options do not accurately define or relate to the process and effects of soil compaction. While soil can change over time and fertilization can benefit roots, these concepts do not address the core issue of how compaction impacts pore space. Similarly, while aeration and drainage are important for soil health, compaction generally impairs, rather than improves, these characteristics.