Some thoughts.
All charges done under terrorism laws are trumped-up charges.
Probably, the sentences were excessive. These ranchers were probably being made an example of to other ranchers in the area.
Let's check for damages done by the fires. If damages were done to public property, restitution should be made by the ranchers.
If the fires were done on public property under contract to the ranchers, they may have broken some terms of the contract.
If the property was wholly owned by the ranchers, and if they had the fires completely under control, the judgment was unjust.
If there was no harm to people, or damages done to property of others, the ranchers should have brought, and still can bring, claims of unjust complaints against them by whomever brought the complaints against them in the first place.
The point is, we don't know enough about the details of this case to make a right judgment... except in one area. The usage of terrorism laws should be against the legal system whenever it is used in this manner.