Arborist

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.

When to call an arborist

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.

How to select an arborist

The most common abuse of a tree is a practice called "topping" in which the outer part of the branches is cut off. This has several bad effects. It deprives the tree of leaves, starving it and making it more susceptible to insects and fungi. Since most of a branch is intact, the sap continues to flow to the end of the branch, encouraging new growth to be small, weak bushy sprouts at the end of the cut branches. The new weak branches shade each other and are ugly.

Branches should be removed so that relatively few, large branches remain. The branches that remain should retain most of their leaves. Ideally, the tree will be shaped away from wires, buildings and human spaces. It should become more open and yet remain natural-looking.

Finally, most of the "arborists" that are unskilled-enough to top a tree, also fail to protect the heartwood with paint or pitch. Most often they leave it exposed to rain, rot and boring insects.

Correct trimming removes smaller branches near the trunk. A cut should be made vertically or be slightly overhung to keep water out of the heartwood. Bare heartwood should be painted to discourage insects and rot. The paint is more critical as the cut is closer to the trunk, and heartwood or the climate is more wet. Some trees have wet heartwood, and a cut must be painted or pitched.

A professional arborist will not leave branches on the ground, to be a safety hazard or nuisance. If he cuts down a tree, he will know how to remove stumps. He will also have a truck with a chipper, and clean up after himself.

Lastly, be sure to ask if the arborist carries insurance. In some jurisdictions, unless you make other arrangements, as his employer you will be responsible for his care if he has an accident while climbing your tree. If he is going to remove a tree near a building, be sure he is bonded.

Legal issues

Depending on legal jurisdiction, there are a number of legal issues surrounding the practices of arborists and of urban tree management in general:

• ownership of trees on or near boundaries - neighbours may have legal rights regarding trees which adjoin or overhang their property.
• "right to light" - some jurisdictions grant property owners rights to enjoy a "reasonable" amount of sunlight, and neighbouring trees which deny this may be subject to trimming or felling as a consequence.
• structural impact - the growth of tree roots (or their removal) may affect the stability of nearby walls or building foundations. Equally, unstable, diseased or dead trees may fall, causing structural damage or personal injury.
• control of disease - in an attempt to control epidemics of tree diseases or agricultural pests, many jurisdictions require property owners to ensure their trees are healthy and that rot and disease are controlled.
• conservation - in many locations, certain trees are protected (often on a basis of species or size), requiring a specific permission be obtained before they are felled or radically trimmed.
• safety - property owners are generally liable for injuries arising from unsafe trees or tree branches, and may also be liable for the safety of arborists working on their trees