At least in the West, the vast majority of forestry land is managed by the NFS. Private land is really only used for Christmas tree farms or specialty trees for the paper industry.
For public lands, the timber industry is responsible for their own replanting, but it's largely irrelevant. More timber is lost to wildfire than logging every year, so most replanting falls on the Forest service anyway:
https://www.usda.gov/sites/default/files/documents/reforesta...
Edit: Apparently this is all wrong and out of date!
While the NFS still owns the majority of forestry land in the West, it only accounts for a tiny portion of the overall lumber produced. From the CRO:
> Since the 1990s, FS timber production has decreased, totaling around 2 billion board feet annually since FY1999.56 In 2011, NFS supplied 2% of U.S. wood and paper products. The decline is attributable to a multitude of factors, including (but not limited to) changing legislative directives and related forest management policies and practices—such as increased planning and procedural requirements—as well as changing market dynamics for wood products, public preferences, and litigation.
Basically, it became too hard to log NFS land, so logging companies turned to private or state lands instead (and states set their own criteria for how private forestry land needs to be replanted).