What are the thermal R-values for wood?

USDA Forest Products Lab Wood Handbook, Table 4-7 entitled Thermal conductivity of selected hardwoods and softwoods lists thermal properties for various species of wood. The table is available online as a PDF file at:

Canadian Wood Council has a Technical Bulletin on Thermal performance of light-frame wood assemblies. It discusses an R value of 1.5/inch of thickness for wood products:

Also, from 1993 ASHRAE standard, the R value per inch of thickness is about 1.1 F*ft^2*h/BTU per inch of thickness.