One hundred years ago a sixth of the area of Paris was used to produce annually more than 100,000 tons of high-value, out-of-season, salad crops. This cropping system was sustained by the use of approximately one million tons of stable manure produced each year by the horses which provided the power for the city's transport system. Sufficient surplus “soil” was produced to expand the production area by 6% yr−1. In energy, mass and monetary terms the inputs and outputs of the Parisian urban agro-ecosystem exceed those of most examples of present-day, fully industrialized crop production. The productive biological recycling of the waste products of the city's transport system contrasts favourably with the requirements and consequences of the simplified, present-day urban ecosystem.
