clear-cutting and removal of birch was detrimental to the long-term productivity of the forest. The numbers showed that forest growth declined with each successive one-hundred-year cutting-and-weeding cycle. Without the companionship of birch, with its microbes transforming nitrogen along mycorrhizal networks and bacteria helping guard against root disease, the growth of pure Douglas-fir stands declined to half of that evidenced in mixtures with birch. Birch, on the other hand, maintained its productivity without fir.
