Topping Versus Crown Reduction
To avoid harming a tree while pruning, make sure to never top it. Topping usually ends up killing the tree because it leaves large, open wounds which are easy entrances for pathogens. In addition, topping is only a short-term solution and you will soon have to top it once again. When you top a tree, you only transform it into a short-lived hat rack. Certified arborists know that instead of topping a tree, one should use the crown reduction technique. Crown reduction at a smaller spread and smaller height is the best solution, short of removing the entire tree.
Tips for Crown Reduction
For attractive and effective crown reduction, avoid heading cuts; never just lop off branches at a set height. Professional crown reduction uses drop-crotch pruning, in which you go down the branch to a lateral branch that is no less than one-third the diameter of the original limb and make the cut there. By doing this, you reduce the height of the tree because energy now goes into the lateral branch. The resulting wound has a better chance of compartmentalizing and forming callous tissue if you do it where there is another lateral branch.