I doubt anyone would consider leaves a nuisance, and I doubt there's ever been a reported case on it, but your case may be so extreme and may cause so much actual damage that it might qualify.
See CA Civil Code sections 3346 and 3479, and CA Penal Code section 384(a), and the case law cited in the annotations, and do some free research on lexisONE.
I'm only licensed in CA. Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
I researched this issue but did not find any case law in the California reported cases on the issue of whether tree leaves were found to constitute a nuisance under California law.
I think nuisance claims are extremely fact specific, and will depend upon whether the neighbor acted reasonably.
Notwithstanding the lack of case law, I think you won't be able to prove much by way of monetary damages.