We have a row of several spruce trees that were already mature when we purchased this property 35 years ago. At that time there was nothing behind us but woods not even any access roads. It has since been developed. When the lot behind us was cleared for building they shaved the overhanging branches right down to the trunks. This was done without our knowledge or permission. They crossed over the property line to do this as the trees are completely on our property. We were warned they would die. They did not and have since grown new branches. We did not pursue the issue at that time. We since have a new neighbor behind us. They put up a chain link fence just 24 inches from the tree trunks. We could no longer easily do any trimming on that side because it is too tight to get between the trees and the fence. The neighbor is demanding that we trim back the overhanging branches as he says they are killing his landscaping. We contend that he knew the trees were there and should have planted accordingly. We purchased a gas powered tree trimming pole and trimmed back what we could safely reach. We repeatedly asked him to work with us to insure he would be satisfied but he refused saying he was too busy. However the electric, cable and phone lines are mixed in with the higher branches. I had the power and phone people out to look it over and they will not do any maintenance trimming but warned me they would come after us for any damages. We feel we have trimmed the branches enough that his lanscaping is only shaded part of the day and none of his property was ever at risk. He however is insisting that the higher up branches also be trimmed and wants us to hire a bonded tree trimmer. I cannot afford to do that. He says he is going to invoke "self-help", hire one and bill me. I warned him that I will sue him for removal and replacement if any of the trees are irreparably harmed. I guess he will be taking me to court over the tree trimming bill. Do I have any recourse?

This is actually an addendum to my question. I forgot to mention that I live in Hermitage, PA Mercer County

You are not responsible for trimming what hangs in his yard, nor providing sunlight to his yard.
He can trim all he wants, but only straight up in the air at the property line. If your trees die because they were too close to the line and he trimmed all one side, that is not his liability. He cannot step over the line if it gets to that. As you say, it would be better if every neighbor could work together on boundaries. But it does sound like your trees were planted too close to the line, if 24" is the distance from spruces to fence. A spruce should have been planted at least 6-8' away from the line.

As for utility lines: they can and will charge you for keeping the lines clear if you don't do it.

The trees can be trimmed on his side but he can't just hand you the bill for doing it. He is responsible for paying that bill - not you and even if he takes you to court you still don't have to pay.

Now for the utility company trimming your trees and handing you the bill - yes, you do have to pay that bill. And remember when it gets cold and there are ice storms or heavy snow and your trees snap a line or take an entire pole out you will be responsible for that bill which can be pretty steep. Keep that in mind when it comes to this winter and possible damage your trees may do then to the lines/poles.

First, I would check with the agency that oversees the utilities. The electrical company does trimming for free. In fact, when a tree limb of mine broke off ant took out a power line for most of a day, I was never billed anything. The utility cleared the branch, but left it in my yard and I was responsible for clearing it, but that was it.

Are you sure the property line is correct?

But you are not responsible for the trees interfering with your neighbor's landscaping. He can trim anything overhanging, bit can't trim to the point it kills the tree.