Permaculture - an idea that began around sustainable agriculture - is moving into the urban environment.

  You can also learn more about this subject at the Oakland-based Urban Permaculture Guild.

Dave Henson, Executive Director of the Occidental Arts and Ecology Center (right), explains that interest in permaculture arose in part in response to the widespread dominance of "monoculture," or large-scale farming of a single crop.

One of the enduring examples of crop integration is indigenous to Mexico and the American southwest, and known colloquially as the "three sisters."