Trees and shrubs can suffer injury from mechanical error; everything from paving to weed whacking can cause damage to a tree. The best way to prevent damage is understand your trees growth habit.
The root zone of the tree spreads a little further than the canopy of leaves or needles above (also called the drip line). Placing heavy equipment or items directly over the root system can cause soil compaction and damage to the root (which may lead to tree decline or death over time).
Be careful not to push mowers, weed whackers or other maintenance equipment into trees as it will cause damage to the trunk which may, over time, cause the trees decline.
Driving a vehicle over the root zone of bumping the tree with a vehicle will cause significant damage.
Wrapping the tree with plastic, metal, heavy cloth, wire or other non-biodegradable material will result in girdling (the trees continued growth - deforming as it encompasses around an object - which can restrict water and nutrient flow throughout the tree).