The four levels of accreditation recognize arboreta at various degrees of development, capacity, and professionalism. Accredited arboreta are encouraged to seek and achieve higher professional standards and move up through the levels. Categorization also allows an assessment of which arboreta are capable of participating or collaborating in certain scientific, collections, or conservation activities.
Level I arboreta are generally smaller publicly accessible sites with at least 25 species of woody plants, one or a few employees or volunteers, a governing body, and an arboretum plan. Examples of arboreta at this level may include golf courses, college arboreta, cemeteries, zoos, private estates, or towns with an organized tree collection.