If you go to the Database for Michigan look at the right for DNR click on that
you will see the WIKI go there
here is a link:
Department of Natural Resources and Environment (DNR) (MI) - The RadioReference Wiki as it can be tricky to find.
The wiki says a skidder is a 58 unit, so if its the Roscommon skidder, they would go by "Roscommon 58"
I have heard of '57' or '57b' units but I don't know what those are, and it's not listed in the wiki.
I live in northern lower, so a lot of the traffic is on FMLP (1217) which usually has Station 16 dispatch and higher level supervision. Let's say there is a fire in the Roscommon service area, Roscommon units would usually be on FMROSCO (4068) and if air units were providing support they would also go on 4068/FMROSCO. From what I can hear from at my house, the local DNR units are also be paged by local county dispatch and the supervisor and they will talk with county dispatch and other responding FD's on the local groups.
The map
here shows the service areas, so you probably want plainwell?