Tree root damage to neighbor's driveway

[Angela A.]

A neighbor of a rental property that I own, sent a letter through certified mail (received in my mailbox without my signature) and notified me that roots of a tree on my rental property has caused extensive damage to his driveway. The tree was there when I bought the property 20 years ago, but I don't know what the condition of the neighbor's driveway was at the time. The property has been managed through a property manager the whole time, so I don't know what the tree looks like now. He is threatening me that he will take court action if I don't pay for the damage of his driveway due to the root damage, but I was wondering what California law generally says. I was trying to research online and it was mentioned that the neighbor that has incurred damage could have hired an arborist when he noticed a problem and have the roots trimmed before it led to more damage. I also don't know if there were signs that there was already a problem from the tree roots when the neighbor purchased the property. He says that the tree roots have caused "extensive damage", but why did he wait that long to inform me as roots don't cause damage to driveways overnight. It appears that California Law protects the vitality of the tree in that the neighbor has to ensure that cutting the roots does not damage the tree. My question is how much validity does this neighbor have in collecting for the damage to his property and what action do I need to take? Also, does rental property insurance take care of this? I have an umbrella policy. If anyone has experience with this or has knowledge of California Law, I'd really appreciate it!

[Henry T.]

Quote from @Angela A.:

Thank you for your reply, Henry. I am willing to remove the tree now that I know that it may potentially create more problems in the future. I just don't feel like I should pay for his driveway since he's owned the property for almost 20 years, the tree was there when he bought his property, he waited until there was "extensive damage" until notifying me, and he didn't take any proactive action to take care of the root invasion himself before it became a real problem. 

 No, I don't think you owe him anything. It's very nice of you to remove an encroaching tree.  He needs to be vigilant on his part to protect his property. He could have put in a barrier to stop the roots, or chopped them long ago. A hassle for him, yes,  but that's the way it is.  If the tree is gone he won't have to deal with it further. Nice on your part and respectful of your neighbors property line.