Under Massachusetts common law, you may remove branches of a neighbor’s tree extending over your property line as long as you don’t kill or damage the tree. Also, the neighbor has no liability for roots growing into your yard and causing damage. Massachusetts law does not allow a person to cross or enter a neighbor’s property for these purposes without the neighbor’s consent, nor to remove any branches or other vegetation within the confines of the neighbor’s property. This is the “Massachusetts Rule.”
This wouldn't be the first time the City of Somerville overstepped it's authority.
no subject
http://www.lawlib.state.ma.us/subject/about/trees.html
http://massrealestatelawblog.com/2013/01/27/check-before-you-cut-massachusetts-illegal-tree-cutting-carries-substantial-civil-penalties/
"Branches Over The Property Line
Under Massachusetts common law, you may remove branches of a neighbor’s tree extending over your property line as long as you don’t kill or damage the tree. Also, the neighbor has no liability for roots growing into your yard and causing damage. Massachusetts law does not allow a person to cross or enter a neighbor’s property for these purposes without the neighbor’s consent, nor to remove any branches or other vegetation within the confines of the neighbor’s property. This is the “Massachusetts Rule.”
This wouldn't be the first time the City of Somerville overstepped it's authority.