An arborist (also known as a tree surgeon) is a professional who maintains trees (generally in an urban environment). This includes planting, trimming, pruning, shaping, and felling trees, the treatment of disease and decay within a tree, and the excavation and removal of tree stumps and roots. This differs from forestry in that it is done generally for safety or aesthetic reasons, not for commerce.
If you can't see sky through a tree, it probably needs to be trimmed. Trees require trimming to keep them away from wires, fences and buildings, to permit people to walk and sit under them, and so that the trees can gather light more efficiently.
The best time to trim a tree is before the sap rises, in early spring. The tree is in a sort of natural anesthesia, it's past the stresses of winter, and it has the entire growing season to recover. Late fall and winter are good for a tree, but sometimes tough on the arborist.
You should call an arborist if your tree catches fire, is split by lightning, or broken by a storm. Dangling parts are a real hazard to passersby and buildings. If the tree is old or valuable, a skillful arborist can sometimes bind, glue, bolt or guy it so that it can heal. More likely, he can tell you how to trim it to be safe, and whether it must be removed.
Lastly, some arborists also install tree-house foundations. Amateur tree-houses are spiked to trees. Professional tree-houses are cabled to the trees, through steel pipes inlaid and glued in holes bored through the center of a trunk or branch. The cables simplify the tree house (it can have a standard floor structure bolted to the cables) and put less stress on the branches. The pipes protect the tree from chafe, insects, rot and moisture. The pipes should be slightly angled so rain runs out.When to call an arborist