There is a clear distinction between the new and old-growth 2by4s. The main visual difference is observed in the width of the annual rings. This video compares the mechanical properties of today's dimensional lumber with the old-growth dimensional lumber used in the early 20th century. The results show a clear winner when it comes to strength. This is because most of today's lumber is sawn from trees that are at most 50-60 years old whereas the old-growth lumber was sawn from forest that were at least double that age. This reduction in strength could potentially impact the framing and quality of new houses.
References:
[1] R. Sedjo, "From foraging to cropping: the transition to plantation forestry, and implications for wood supply and demand," An international journal of forestry and forest industries, vol. 52, no. 1, 2001.
[2] B. Loucks, "Growing Douglas Fir," in Forest Management for Small Landowners, 2020, pp. 1-30.
[3] J. Dinwoodie, Timber: Its nature and behaviour, London: BRE, 2000.
[4] R. Kennedy, "Coniferous wood quality in the future: concerns and strategies," Wood Science and Technology, vol. 29, pp. 321-338, 1995.
[5] H. D. Erickson and A. T. Harrison, "Douglas-Fir Wood Quality Studies Part I: Effects of Age and Stimulated Growth on Wood Density and Anatomy," Wood Science and Technology, vol. 8, pp. 207-226, 1974.
Download references here:
https://drive.google.com/drive/folders/1oqSJ6FgpbRFA_Gs3ISewu9Y-S2zCLRl_?usp=sharing