From Consumer Wiki
The California Department of Consumer Affairs, Contractors State License Board, licenses individuals who perform tree maintenance and service.
Tree Service (Contractor) License is required for tree trimmer, which includes; tree removal, tree pruning, stump removal, or engages in tree or limb cabling or guying. The term "contractor" includes maintenance and service; does not include a nurseryman whose routine work includes the same incidental service or a gardener whose normal course of routine work may include incidental pruning of trees measuring less than 15 feet in height after planting.
Contractors State License Board
9821 Business Park Drive
Sacramento, CA 95827