Tree surgeon
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 depends on the species of tree and the purpose of the pruning. A thorough knowledge of the local species is necessary to determine the best timing.
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 often 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.
Pruning should only be done with a specific purpose in mind. Thinning of a tree is often unnecessary. Removal of small internal branches can be detrimental to the tree?s health, by causing remaining branches to grow long and narrow, without much taper. These branches are more susceptible to breakage, especially in strong winds.
In recent years, research has proven that wound dressings such as paint, tar or other coverings are unnecessary and may be harmful to the tree. The coverings may actually encourage the growth of decay-causing fungi. Proper pruning, by cutting the branches at the right location, can do more to limit decay than any wound dressing yet devised. Trees do not respond to wounds as animals do, and treatment by covering the wounds, as with people, is not a sound arboricultural treatment.
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.
The International Society of Arboriculture, a non-profit organization, maintains a list of ISA Certified Arborists who have passed a written exam and demonstrated a basic level of knowledge in arboriculture. The list of ISA Certified Arborists can be found on their web site at
The American Society of Consulting Arborists also maintains a list of Registered Consulting Arborists. This site can be accessed at
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
