Self-provisioning does not increase in line with population Growth
Particularly in the capitals of Australia and Japan, where the population has increased tremendously over the past 40 years, the self-provision has declined; in Canberra from 150 to 90 percent and in Tokyo from 41 to 27 percent.
This is despite the increase in yield of agricultural land per hectare. Copenhagen on the other hand, has increased its self-provision slightly from 34 to 45 percent because its population has remained fairly constant.
"When the local capacity to supply a city declines, it becomes more dependent on the global market. As an example, Japan imported wheat from 600,000 hectares of foreign farmland to meet the demand of their capital and surrounding region in 2005. This means that large cities should now start to invest in urban agriculture especially if climate change has large effects on food production and other parts of the food chain in the future,” says John R Porter.
The study has exclusively focused on the historical and current production and not considered whether changes in land management practices can increase productivity further or whether consumers are willing to limit their intake to local seasonally available goods. It did not include citizen-based production from allotments, urban gardens etc.Read more at: http://phys.org/news/2013-12-scientists-food-self-provision-major-cities.html#jCp