Jay, Most available data regarding hardwood diameter growth rate for Illinois timber trees shows a .1" - .2" per year diameter increase, or 5-10 years to grow an additional 1". Not sure how that compares to the growth rate starting from a 1 year old tree, but i cant imagine it takes 100 years for a hardwood tree to obtain a 20" diameter? Or does it?

Chuck:

Just remember those data represent average values: on average, half your trees will exhibit growth rates in excess of those estimates and half your trees will exhibit growth rates lower than those estimates For example, some northern red oak trees may reach >28” dbh in 80-90 years, whereas other northern red oak trees, in the exact same stand, may only grow to be 10” dbh after 80 years. Why such the disparity in growth rate?

Growth rate, or radial- or basal increment, is a function of an assortment of interacting variables: species and existing stand conditions (genetics, stand density and competition, stocking levels, canopy position, live-crown ratio, etc.); topography and soils (hillslope position, site index, soil moisture and drainage, pH, fertility, etc.); weather (strong winds, ice damage to crowns, excessive heat, precipitation patterns and events, etc.); insects and disease; past high-grade logging removing the most vigorous species in the stand; etc.

That calculation seems like it would be direct opposition from being able to count the rings in a fallen oak to determine it's age in years. (if in fact the ring counting thing is legit and not just something I've always hear from people older than me.)

I say this because assuming the .1" growth above, the ring for a year would only be spaced .05" from the next ring or roughly 3/64 of an inch. I'm not sure that rings that close together would even be discernible.....would they?