While this does not discuss the reasons for requirements, however it does list the minimum requirement of "100 hours within the previous 12 months" as a requirement for interagency carding for fire operations in the U.S.
A type II CWN contract can be downloaded here:
Type II Contract
Even though this is a Type II contract, the pilot requirements are the same for all contracts. (I was unable to find any other contracts on-line). Go to page 30 in the document, (will be 51 of 135 in pdf format), to Section D—Pilot Requirements Experience and it shows the requirements in detail. This is a basic summary, read the document for ALL the correct info. All times are helicopter:
Total Time:...................1,500
PIC..............................1,500
Preceding 12 months.........100
Weight class....................100
Make & Model....................50
Turbine...........................100
Mountain.........................200
Mountain Make & model.......10
Long line VR......................10