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I am sorry to hear about this situation. As discussed in Carvalho v. Wolfe, 140 P. 3d 1161 - Or: Court of Appeals 2006, someone in your situation has the following options:
1) Use own labor or hired labor (for reasonable price) to cut the roots from your side of the property, and
2) Pursue the neighbor for reasonable cost of doing so.
One cannot cross over to their property so the work must end at your property line, and one must ensure not to cut anything on their property.
So yes, the neighbor may be liable for the reasonable costs for one having to take out the overgrowth.
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