Timber Tax

Department of Revenue Chapter 150 Division 321 Timber Taxes 150-321-0200
Forestland Valuation Rule
https://secure.sos.state.or.us/oard/viewSingleRule.action?ruleVrsnRsn=21392

Forest Land site classes: http://www.oregon.gov/DOR/programs/property/Pages/timber-classes.aspx
Forestland in eastern Oregon is not assigned productivity classes. Consequently, there’s no FX classification. However, at least 80 percent of the total area must meet minimum stocking requirements. For details on stocking requirements, see page 2-8 of our Forestland Manual, 150-303-424.

https://www.oregonlaws.org/ors/2015/321.257 
"Land class" or "land classes" means one of the eight classifications of forestland, used for assessment purposes by the department, based upon State Tax Commission Valuation Division Supplements published in 1967, and identified in ORS 321.210 (Proposed specially assessed values)."

https://www.oregonlaws.org/ors/2015/321.216