"...mein Acker ist die Zeit", Aufsätze zur Umweltgeschichte - Oapen

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Table 4. Population densities per square kilometer in selected cities by years. Source: Data
taken from www.demographia.com As any demographic data, also those provided
by demographia.com are criticized for various reasons, mostly for occasionally
inclusion of peri-urban areas of unknown size. However, the advantage is that
those data are easily accessible, they are correct at least within an order of magnitude,
and they are arranged in a suitable way. Since they are also used by government
and academic bodies, they are considered to be reliable by and large.
City 1600 1800 Current
Berlin 3,800 (2003)
Buenos Aires 904 (1869) 13,883 (2001)
Kolkata (Calcutta) 33,000 (1991)
London 20,0000* 34,749 (1821) 5,901 (2001)
New York 101 (1800) 10,238 (2000)
Paris 96,512 (1637) 15,851 (1801) 20,240 (1999)
Tokyo 5,517 (2000)
Note: * number of residents only, as area is unknown
These numbers considerably exceed the carrying capacity for humans of the surrounding
areas of towns, as estimated above. Already by the high Middle Ages
cities in Europe greatly exceeded the carrying capacity of non-urbanized areas.
Benevolo 211, for example, counted 100,000 residents in Florence in the middle of
the thirteenth century, living on not more than two square miles. The computed
surface area value per resident is 48 square meters (57 square yards), but this would
include the total area of the city surface, even the Arno River. Such a high biomass
concentration is surprising given infrastructure and transport facilities of that time,
but these obviously coped successfully with the necessary and extended flows of
matter and energy.
I try a different approach by taking biomass as a standard. The tropical rain
forest, which is the ecosystem of highest biomass concentration on earth, contains
around 800,000 kg of biomass per ha (2.47 acres), including all organisms except
those in the soil. I take this as the maximum “natural” biomass ratio. The biomass
concentration in temperate forests is of course lower at around 150,000 kg/ha [i.e.
15 kg/m 2], but this may be considered the maximum “natural biomass ratio” in
temperate European regions. Industrialized contemporary agriculture produces
biomasses of up to 14 kg/m 2 (grain and straw) and 25 kg/m 2 (energy maize), which
is a man-managed and hence “artificial” primary production.
Assuming an average biomass for a mediaeval resident of 40 kg, Florence carried
almost 0.8 kg of human biomass/m 2. Despite the apparently high number of
residents in thirteenth-century Florence, the biomass ratio (with respect to humans
211 Quoted from the German edition. English edition: Leonardo Benevolo, The European City (Oxford,
Cambridge: Blackwell, 1993)