Landscape contractors, those firms that install the plant materials on such projects, are also licensed by the state. Individuals may obtain this license only after obtaining years of experience and passing an exam covering the principles of landscape installation, and certain specializations such as irrigation. Both landscape architects and landscape contractors have a state board comprised of knowledgeable industry leaders that regulate their work. In Oregon, arborists or tree service companies must also have a license from the state, but in this instance people who work on trees are not legally required to have any formal credentials of knowledge of tree care. Tree service companies are regulated by the Construction Contractor's Board, a state regulatory agency which regulates building trades such as carpentry and concrete work.
Ornamental horticulture is the academic area most specifically related to urban trees.
Forestry, plant pathology and related agricultural sciences are all excellent foundations for arboriculture as well. Bachelor's, master's and doctoral degrees are available in each of these fields. A degree in landscape architecture emphasizes design skills, and does not necessarily indicate a strong background in horticulture. As stated above, the state contractor's exams do not test the applicant's knowledge of trees. ISA is the only entity that certifies arborists and tree workers.