Environmental Engineering Reference
In-Depth Information
American corn has been the country's most important crop. It is grown annually on 30-35
Mha of farmland (about 20% of all arable land), its recent yields have been around 10 t/ha,
and its annual harvest has l uctuated around 300 Mt. The photograph from FREEBigPictures.
com can be downloaded at http://freebigpictures.com/plants-pictures/corn-i eld.
almost any result, the range of outcomes that can emerge from relying on plausible
combinations of defensible methods and published information is still simply too
wide to offer a reliable guidance. Reducing these uncertainties and coming up with
a more accurate appraisal of human claims on the biosphere should be a major goal
of modern environmental science.
Most of this chapter tries to make a small contribution toward this goal. I present
three rather straightforward but fairly exhaustive sets of quantii cations that detail
direct biomass harvests for human consumption and their collateral impacts. The
i rst section quantii es the current extent of global crop harvests and their evolution
during the twentieth century. In the second section I do an analogical examination
of aquatic harvests that are now also included in the expanding aquacultural
production. The chapter's closing section reviews the extent and recent history of
harvesting woody phytomass for fuel, timber, and other uses.
