As you probably well know, financial and biological maturity is a function of (species, site index, topography, stand history, current conditions, and landowner objectives). Let us start with some simple definitions that will not only reinforce what you probably already know, but will also assist our inquisitive readers out there in cyberspace.
Financial Maturity: As best explained by Mills and Calahan (1993), financial maturity is that point in the life of the tree beyond which the expected value increase no longer equals or exceeds the net return that would be obtained if the tree were sold and the cash value were invested elsewhere such as a bond, CD, stock, mutual fund, etc. The age/time to financial maturity usually occurs prior to biological maturity.
Biological Maturity: In contrast, the biological maturity of a tree or a stand of trees occurs when the tree or stand achieves maximum merchantable volume. Financial maturity differs from biological maturity by imposing economic and business management constraints on the “wood” production process (Mills and Callahan, 1993). Old trees typically will continue to grow, but their rate of growth slows.
Based simply on landowner objectives, financial maturity can very from landowner to landowner. On poorer quality sites in Illinois (i.e., low site index), I for example might grow my red oak to 18-20" DBH (diameter at breast height). However, on high quality sites (protected coves, low slopes, north and east aspect sites, etc.), I can easily allow my red oak to grow to 22-26" DBH. This silvicultural philosophy holds true for most species, but will vary between species and genera.
Species in the white oak family (white oak, swamp white oak, bur oak, swamp chestnut oak, post oak, overcup oak, etc.) are typically longer lived trees. In contrast, species in the red oak family (northern red oak, black oak, shingle oak, pin oak, southern red oak, shumard oak, cherrybark oak, northern pin oak, etc.) are typically shorter-lived species. What that ultimately means is the red oak family commonly reaches financial and biological maturity sooner than those species in the white oak family. Have you ever noticed that in most even-aged oak-hickory stands in Illinois that the red oak species are usually larger in diameter than the white oak species? This is not because the red oak species are older; it is simply because the red oak species have a faster growth rate. As a general rule (yes, there are exceptions), faster growing trees tend to reach financial and biological maturity sooner than slower growing trees.
Red oak stands in Illinois may reach financial maturity as soon as 40-60 years, with an optimum around 60-80 years. On quality red oak sites, I like to grow my trees to 20-26” DBH. Note: financial maturity may occur sooner or later depending on market demand and stand conditions. If an ice storm comes in and knocks out 60% of the crowns on my trees, then I will more than likely reevaluate my financial maturity criteria for that stand or species. If the red oak market takes a nose dive, I will again reevaluate my financial maturity criteria to coincide with market supply and demand – no sense selling standing timber when the hardwood market is in a tail spin for that particular species. Northern red oak starts to decline rapidly after the age of 100.
White oak stands in Illinois may reach financial maturity around 60-80 years, with an optimum around 80-120 years. On quality white oak sites, I like to grow my trees to 24-30” DBH because they are generally a longer lived and favored mast species. Based on unpublished data collected by Dr. George Hopper, true white oak has an average age at senescence of 194 years, with an average maximum age of 357 yrs.
Eastern black walnut, on quality alluvial sites, may reach financial maturity within 40-60 years, with an optimum harvest window around 60-80 years. As a rule with black walnut, we try to grow them as big as we possibly can - as long as they are healthy and vigorous. Based on unpublished data collected by Dr. George Hopper, black walnut has an average age at senescence of 131 years, with an average maximum age of 214 yrs.
American beech, although a commercial species, is not commonly thought of as a high-value timber species in Illinois. Based on unpublished data collected by Dr. George Hopper, black walnut has an average age at senescence of 168 years, with an average maximum age of 329 yrs.
Hickory species, again depending on site, may reach financial maturity within 60-80 years, with an optimum around 80-120 years. Depending on my silvicultural objectives for a given stand, I commonly slate hickory trees for harvest once they attain 18-22” DBH, but this varies by species, site, silvicultural objectives, and landowner goals. Based on unpublished data collected by Dr. George Hopper, shagbark hickory has an average age at senescence of 137years, with an average maximum age of 238 yrs.
I hope this helped and as always, please consult a professional forester prior to selling your timber. Trust me, it is in your best financial and biological interest!