Legal Question in Real Estate Law in California

1. If the trees protrude over the property line, you may cut the protruding portion yourself at your expense so long as it would not damage\kill the tree.

2. Generally, the cost of cutting the extending portions is your responsibility, not your neighbors. However, this may be altered by your CC&R's (if you belong to a Homeowner's Association, check them for provisions) or by local ordinance (you would have to check with your city and\or county for rules re trees), or the state law prohibiting private nuisances, if the trees\debris are so extensive as to create a nuisance under California Civil Code 3479, which states: "Anything which is injurious to health, including, but not limited to, the illegal sale of controlled substances, or is indecent or offensive to the senses, or an obstruction to the free use of property, so as to interfere with the comfortable enjoyment of life or property, or unlawfully obstructs the free passage or use, in the customary manner, of any navigable lake, or river, bay, stream, canal, or basin, or any public park, square, street, or highway, is a nuisance." It is not clear that these trees creates a nuisance, but it is possible, especially if they pose a risk of damage to your property or health.

Be very careful taking any action on your own. Redwood and Oak trees are protected in some areas of California. You and your neighbor need to check with your city/county before removing any of these trees. The penalties for removing protected trees can be severe.

Generally, the owner of the tree is responsible for any damage caused by the tree, but dropping leaves or being messy is not likely going to be considered damage. You state that the trees are growing into your property. If they have been there long enough, you may have waived any right to complain about that. There was a case a few years back that involved a tree that encroached onto a neighbor's property for many years. The neighbor finally killed it. He ended up owing almost $100,000 just for that one tree.

Work with the city and your neighbor before cutting or trimming, and make sure you use a certified arborist so you don't kill or injure the trees.