Certified Arborist Practice Test

The correct answer highlights common sources of mechanical injury to trees, which include lawnmowers, weed-eaters, and construction activities. These activities can physically damage the tree's bark or roots, leading to significant harm.

Lawnmowers and weed-eaters often create abrasions on the stems and branches of trees, particularly when operators are careless or unaware of the proximity of trees to landscaped areas. Such injuries can expose the inner wood tissues to pathogens and environmental stress, increasing the risk of disease.

Construction activities can be even more damaging, as they might involve soil compaction, root severing, or physical impact. Heavy machinery can crush roots that are essential for water and nutrient uptake or disrupt the surrounding soil structure, which can impede tree health.

Other options, while relevant to tree health, do not specifically pertain to mechanical injury. Girdling roots and nutrient deficiencies can affect overall tree vigor but are not mechanical injuries. Likewise, disease and pest infestation are biological threats, and environmental stressors, while impactful, refer to broader changes in climate and soil conditions rather than mechanical damage.