Each technology has its own yardsticks, usually yields or profits. But only commercial land uses have any profit, and some of the most important land uses have only spiritual or aesthetic yields. The collective criterion must be something deeper and more important than either profit or yield.
Among the ordinary yardsticks, I can think of but one which is obviously a common denominator of success in all technologies: soil fertility. . . .
What else? What in the evolutionary history of this flowering earth, is most closely associated with stability? The answer, to my mind, is clear: diversity of fauna and flora.
It seems improbable that science can ever analyze stability and write an exact formula for it. The best we can do, at least at present, is to recognize and cultivate the general conditions which seem to be conducive to it. Stability and diversity are associated. Both are the end-result of evolution to date. To what extent are they interdependent? Can we retain stability in used land without retaining diversity also?
from Leopold’s review of A.E. Parkins and J.R. Whitaker, Our Natural Resources and Their Conservation, Bird-Lore, 1937 (excerpted from Aldo Leopold – His Life and Work, by Curt Meine).