One, by reducing the height from the tree you're reducing its over-all weight, and, therefore, reducing gravity's efforts to tug it down the hillside.
Several such companies provide services in mountainous regions or areas which are highly prone to tornadoes, hurricanes or storms.
This is essentially a cleaning process, it involves the taking out the unhealthy branches.
Another thing to give thought to whether you'll find law issues protecting the tree or not. These excesses are carefully marked and take off.
Dormancy is often a period where there isn't any active growth of your plant in reply to adverse conditions. One such disease that may be mistaken as oak wilt is oak anthracnose. This can leave the exact property owner legally and financially responsible for just about any damages.