In misc.legal TheKeith wrote:
snip
My grandfather was a real estate attorney and some years before he died
looked up some law regarding trees and discovered something called "air
rights" or something like that, which basically provided that the branches
of a tree, as long as it doesn't physically touch a neighbors property may
not be cut by that neighbor even if it is "over" their property. I was
wondering if there are any comparable laws regarding the tree trunk itself
and its major roots, which obviously run well under my neighbors property?
Help would be greatly appreciated -- thanks.

Nolo press has an excellent book on Neighbor law. You should be able to
find it in your local library. http://www.nolo.com It covers your topic
pretty well. I don't have a copy on hand or I'd tell you what it says.