Tree trimming, particularly trimming that doesn't remove more than 30% of the canopy of a tree is not typically subject to permit requirements. Removal of trees however, does often require a permit. These permit requirements will vary based on the zoning of the property, the type and size of tree, the location in protected woodlands, riparian areas or other sensitive resource areas, proximity of the tree to a structure and other factors. For a comprehensive list of protected trees, more information on permit requirements and potential exemptions, please visit Sonoma County Tree Permit Requirements.