California residents have the right to trim any portion of a tree they legally own. Ownership of the tree is established by California Civil Code Section 833. Under the guidelines of the civil code, the trunk of the tree determines the legal owner. If the entire trunk rests on one side of the property line, that neighbor has ownership regardless if branches, roots, foliage or any other portion of the tree hangs over the property line.
Under California Civil Code Section 834, both neighbors legally own the tree if the trunk rests on the property line. Therefore, both neighbors have the right to trim the portion of the tree that rests near their property line.
The Property Line
If a tree on one neighbor's property begins to grow or encroach onto his neighbor's property, the other neighbor does have the legal right to trim it back. However, the neighbor is only legally allowed to trim it back to the property line. If the neighbor's tree is near the property line, but not actually crossing it, no trimming can take place by the other neighbor without first obtaining permission to do so. Tree roots that cross over a neighbor's property line cannot be cut, uprooted or in any way destroyed unless the roots are causing damage to that neighbor's property.
Under the guidelines of California Civil Code Section 3346, any neighbor who attempts to trim another neighbor's tree that is encroaching or nearing the property line must make all efforts not to damage the overall health of the tree. This law was created as a result of a California court case Booska v. Patel.
If the tree trimming neighbor does cause damage to the health of the tree, that neighbor will be held liable. Courts can determine the exact amount of liability owed. For example, if the tree was cut in a careless fashion, the tree owner may receive up to three times the worth of the tree. If the damage was done accidentally, as decided by a California court of law, the owner may only be entitled to double the worth of the tree.