In Oregon, minor regulations, such as preservation, are individual from city to city, so I will skip that part.
In Oregon, right now (2007), almost anybody doing tree work and pruning must have a license with the state, and that requires a bond and insurance.
Many tree service / arborists are licensed with the Oregon Construction Contractors Board. It's where the tree services started a licensing process, years after the landscapers started a licensing process with a landscape license board. There are two exemptions:
1. Licensed Landscape Contractor (also with bond and license)
2. "Gardeners" > pruning under 15', pruning cuts under 4" in diameter and removals where trunk diameter is less than 5" in diameter (the little stuff).
The Construction Board does not really have a compentency test for tree services. There is a small test covering laws, rules (more policy).
The Landscape Contractors Board handles landscaping and has several tests comparable to multiple college final exams.
ONLY landscape contractors with the landscape license, can advertise tree planting and transplanting. With the contractors board license, an arborist is limited to the REPLACEMENT planting of trees, not to exceed $500 per year per address.
So the landscape license in Oregon, is the only license that enables the broad scope of arboriculture including pruning, bracing, planting, etc..
Any pesticide application of significance, falls under the Oregon Department of Agriculture, and requires an additional pesticide license for anybody who wants to offer that service. It requires about 2 hours of testing: not easy, but not hard.
Certification is not required in Oregon - yet - but is required in some cities for certain trees, such as street trees, for example.
Why the Construction board and certain tree services didn't initiate licensing under the landscape board originally, is still a topic of curiosity. Because the landscape board was a division of the construction board when the tree service licensing process was put together. Now, the landscape license board is separate.
