Your statement that the Tongass has 17 million acres may be true, but is not accurate if intended to imply that much land is available for timber harvest.  The 17 million acres includes all the mountaintops and glaciers in the Tongass.  The potentially suitable lowest land is 2+ million acres.  If you eliminate the acreage  of forest land  located within land use designations (LUDs) that do not allow timber harvest, etc, you get to an existing timber base- including second growth, I believe- of approximately 600,000 acres.  A far cry from 17,000,000 acres comprising the total forest.

http://www.merid.org/en/TongassAdvisoryCommittee/~/media/Files/Projects/tongass/Ecological/Working%20Forest%20Group%20Old%20Growth%20Land%20Base%20Analysis.pdf