Can I sue someone who cut down a tree on my property?

In California there is a law that establishes that cutting down a tree without an owners permissions allows treble (3x's) damages for the value of the tree and I believe there maybe a recent case for emotional distress damages but that is an iffy damage. To determine the value you would need an arborist to value the tree and if you believe it was the key to preventing hillside erosion, someone with specialty training in soil erosion.

Yes, you certainly can get damages and it should be the price of replacing an oak tree of the same age and height [which probably a tree expert does not know for sure as no one does that, but perhaps they can give an estimate]. You need a declaration from an expert to show the court.

An expert consultant, landscape or arborist may value the tree. You may receive up to treble damages, depending on the evidence.

You can certainly sue. Difficult to assess damages. Small Claims is up to $10,000; if you think the claim is worth more, see a lawyer.

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. The short answer is: yes. However, you would have to find an expert to determine the value of the tree and/or the detriment to your property (Hillside Erosion). I suggest that you contact an experienced civil litigation attorney for a face-to-face consultation and give him/her all of the facts surrounding your case. (S)he would then be in a better position to analyze your case and advise you of your options.