In limited cases: when the threat is so widespread it endangers the general public, you have legal authority to do the work, and you have rights-of-entry and agreements holding the federal government harmless.
Typical situations:
If the criteria aren’t met, the owner may qualify for Individual Assistance instead.
Your legal authority to enter private property, the basis for finding a threat to the general public, and copies of rights-of-entry and hold-harmless agreements.
Use a standard right-of-entry form with hold-harmless language and keep a signed copy for every parcel.