Believe it or not, in the middle 1920's only 40% of a log was converted into primary product of manufacture (lumber, for example). In addition, 23% of the log of 70 years ago ended up as sawdust!
Today in the mid-1990's a typical circular sawmill converts 50% of the log into primary product with band mill conversionat about 57%.
Saw Kerf average 21% for the circular sawmill and as low as 12% for high production band mills.
Obviously, saw mill efficiencies have increased since the 1920s but there is still much room for improvement. In addition, trends such as environmental constraints on timber harvesting, smaller logs from the forest, and an incresed demand for wood products makes it imperative that we improve sawmill efficiencies.
The good news is that technologies currently exist that can enable 70% or more conversion efficiencies at US sawmills. Forest Service article.
The US annual cut of timber for lumber products is equivalent to approximately 240 million trees. However, if our sawmills operated at a 70% recovery efficiency, we could get our annual harvest of lumber from 171 million trees. Thus, we could save the equivalent of 69 million trees annully if our recovery effiency improved from 50% to 70% in our primary processing industry.
In addition, these same 69 million trees, if permitted to grow in the forest, would continue to absorb about 900,000 tons of carbon dioxide and produce about 650,000 tons of oxygen each year.