There are some very good things you can do to promote heathly, long-lived trees. And there are a number of things you will want to avoid. If in doubt, call a member of the National ARBORIST Association for advice specific to your region and variety of tree or shrub.
First and Foremost ~ Topping...Don't Do It!
Topping or stubbing are examples of removing large branches from mature trees. A topped tree is a disfigured tree and although it was intended to help the tree, the opposite is the result.
When a large amount of a tree's canopy (umbrella) is removed, the crown to root ratio is imbalanced and this adversely affects the tree's nutrition. It also exposes the tree to the sun which can result in scalding. Topped trees develop multiple branches or suckers, at or near the pruning cut. These branches generally are weakly attached and are prone to failure.
A topped tree is also vunerable to disease as the stubs have a difficult time forming protective callus and this invites invasion of fungi and insects. The location of the topping cuts may also prevent the tree's natural defense system from doing its job.
Finally, topping trees represents an unwarranted expense. A topped tree will often grow back to its original height quickly, and it will be more dense than one that has been pruned correctly. Other costs may be hidden, such as loss of property value that a well-maintained tree will encourage. There is also increased hazard from branches that have weakened as a result of the topping.
Wounds made by climbing spikes invite infection. There will be holes in the tree bark. These injuries often do not repair efficiently or effectively.
Lawn mowers and string trimmers hitting the bark of a tree can severely damage the inner bark and cambium near the soil line. This damage invites insects and fungi infestation. The best advice is to remove sod from around the base of the tree and replace with mulch.
Compacted soil is not easily penetrated by water and air, the two basic needs for strong, healthy roots. Soil compaction can be caused by heavy equipment used near a tree, concrete over the root zone, even foot traffic can cause soil compaction. Do not store items by the tree.
Take Care with New Plantings
Do not plant a new tree with a wire basket, rope, or anything that may constrict or "girdle" the roots. Girdled roots seriously affect the health and the stability of a tree. Plan where you want to plant a new tree based on its type and mature size. Be cautious when planting trees near a home foundation, patio, driveway, under power lines, or under a home's eaves.
Too much fill over a newly planted tree's roots can cause damage, and may even kill some species. Take care not to plant tree too deep.
Building foundations, driveway, sidewalk & road excavation are common events that can cause serious damage to a tree's root system. Construction damage may not be immediately noticeable, but over a period of years the health of the tree will decline as a result of root damage.
A prized tree may be inadvertently, but fatally injured when care is not taken during excavation or construction. If you are building near an existing tree, consider calling an arborist to advise on the project during the planning phase, before any work has begun.