The Tree Care Industry Association, formerly the National Arborist Association, is a public and professional non-profit organization for the arboriculture field.
It has more than 2,000 member companies representing over a dozen countries. TCIA’s Accreditation program certifies that tree care companies that have been inspected and accredited based on adherence to industry standards for performance and safety; maintenance of trained, professional staff; and dedication to ethics and quality in business practices. In addition, they provide safety and educational programs, guidelines for tree service operations, ANSI A300 tree pruning standards, and consumer resources.
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.
Choose a job you love, and you will never have to work a day in your life. - Confucius
There are also additional classifications of certified arborists with Certified Arborist/Utility Specialist for those who work near power lines, and Certified Arborist/Municipal Specialist for those who deal mostly with community trees. Other certifications exist for Certified Tree Workers, and the highest level of certification, the Board Certified Master Arborist.
The American Society of Consulting Arborists is an organization whose membership is exclusive to those with either a certain level of industry experience, plus higher educational experience or continuing education; some members may achieve a higher status by fulfilling the requirements to become a Registered Consulting Arborist. Consulting arborists generally specialize in the areas of ethics, law, land planning and development, and tree valuation, among others. Consulting arborists are often called on for legal testimony and report writing in various instances where a particular authority on trees is necessary for consequent actions.
In the UK, the principal organisation representing arborists is the Arboricultural Association. The association maintain a register of consultants who have demonstrated a high level of technical arboricultural knowledge, and operate an Approved Contractor scheme. This scheme assesses both the technical competence and business practices of arboricultural contractors.
The European Arboricultural Council is a European group of arboriculture organizations from various countries.
Plant Amnesty is a public education and advocacy group, based in Seattle, dedicated to promoting proper pruning methods. Founded in 1987, Plant Amnesty became an international resource for arborists and their clients in the mid-1990s.
Source: Wikipedia. http://en.wikipedia.org/wiki/Arborist