Heavy objects driving over their roots, particularly close to the trunk. Root zones can extend out 2-3 times larger than the crown, the leafy diameter of the tree.
Lawn sprinklers that are constantly making the lower trunk and root flare wet.
Transplanting too low.
Regrading that buries the root flare and part of the trunk. Death may result.
Bark injury due to string trimmers or lawn mowers
Permanently tying wires around trees that limits the flow of nutrients as they grow.
Leaving certain types of baskets, cages and balling products on when transplanting.
Killing off the microbes in the soil.
Too much compost piled up around the truck.
Digging in the root zone, particularly close to the trunk. Cutting off or damaging a large support root may be equivalent to removing an arm or leg from a human being.
Excessive pruning - no more than 1/3 of the crown.