The answer may depend on the answers to still more questions.

First: Where is the tree? If it is on your father's property, he will likely be responsible for the tree removal cost all by his lonesome. But if the tree straddles the property lines, then the neighbor is a co-owner and is responsible for sharing the cost of upkeep and removal if necessary.

Also: Who will be affected if tree falls? Owners are expected to protect their property when they can. But how about power lines and telephone lines? Is it possible that the tree might fall on a city sidewalk or street? In such situations, help might be available from the city or the local utility company.

It's good that you're taking steps to deal with the problem, because this tree may pose one lollapalooza of an expense it it falls on a house -- well over the $4,500 quoted in removal costs. An owner who knows the tree might fall will likely still get some relief from insurance for damages caused, but in some cases the owner could also lose the homeowners' insurance. Also, if the tree damages someone else's property or injures someone, and your father knew that danger was imminent, he could be held responsible for compensating the injured party.

When money is a big factor, it may be worth trying mediation. It has a way of enforcing creative solutions that courts might not divine. For example, your dad's neighbor might be willing to foot the bill and be paid back in installments over time.

For more information, check out the following: Trees and Neighbors FAQ, Boundaries and Neighbors FAQ, and Nolo's Mediation area. If you still have questions, consider purchasing Neighbor Law: Fences, Trees, Boundaries & Noise.