Aker said the biggest tree-killer is, by far, root damage by the owner. And tree-maintenance is mostly for the birds. Trees generally do not require water in addition to the amount they get from Mother Nature, except in times of draught, said Aker. Fertilizer and mulch are in the same category. Prune out dead branches for safety purposes and try not to disturb the root system.
Several factors can be at the root of a root problem.
A car parked under your tree. For example, planting a cable line or new drainage line can cut into tree roots and eventually result in the death of the tree. Dicamba is one example of a root-killing herbicide that could damage a tree if misplaced. But too much mulch can cut the roots off from water and oxygen. Though several factors can disrupt a tree's root system, one of those things is not other trees.