Yes, all timber harvested in the state of Illinois is subject to a 4% timber harvest fee. Technically, this is not a fee, rather it is a yield tax. More than likely this "name game" was an attempt to get the measure to slide through the state general assembly unnoticed by "tax" hawks.
Illinois has a forestry program entitled the "Illinois Forestry Development Act." This program is designed specifically for woodland owners with manage 10 or more acres of forest land dedicated to timber production, wildlife habitat, recreation, and ecosystem services such as clean water and carbon sequestration.
Landowners must develop a forest management for their land and they must follow the plan to receive their preferential property tax incentive: a 1/6 equalized assessed value assessment as cropland.
Please contact your local IL-DNR district forester for additional information regarding the Illinois Forestry Development Act:
IL Technical Forestry Assistance Directory: http://web.extension.illinois.edu/forestry/pdf/tfb-nres-201-13.pdf
Preferencial Assessments for Wooded Acreage: http://tax.illinois.gov/Publications/Pubs/Pub-135.pdf