I'm guessing you aren't from the U.S. but in the southern U.S. growing newer species of Pine (variants of Loblolly Pine). A standard lease is 20 years from seedling to harvest, some older variants can go 30 to 50, but you don't see that being planted any longer and that's all leases maturing.
And here, I can assure you they are very much mono culture, evenly spaced, engineered species of trees, almost nothing else happens on the land in that time period. (generally it looks pretty similar to this https://a.rgbimg.com/users/p/pa/paparabbit/600/mwYGk8q.jpg) They do come and selectively thing at 5, 10, or 15 depending)
See the issue is, at least in the southern U.S. they clear cut nearly everything in the 1800s. There is very little old growth left.