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

132
tion densities open up possibilities for epidemic pathogens (some of which in fact
emerged only in urban times) as well as for opportunistic pathogens.
2.6 Time
Ecosystems are related to time by their stages of maturity. Imagine the initial stage
of a future forest, an ecosystem that has an average “life expectancy” of around
300 to 600 years, if it remains untouched. During the initial 10 percent of the time
span the floral diversity increases dramatically, but it declines soon after. Some
species will be replaced by others. Therefore the maximal and final plant diversity
is only reached slowly and does not take place before the final 20 percent of the
life span of the system. Similarly, in the case of the fauna there is initially a moderate
diversity of species; this then decreases and later increases faster than the plant
diversity. The maximal and final diversity likewise reached roughly during the last
20 percent of the life expectancy of the ecosystem.
The example aims to show that there are three different scales of time. One
timescale affects the shape of continents, mountains, and rivers and is almost
without influence (despite some mythical narratives) for humans. This is the geological
time. For humans, cycles as described in the forest example are, however,
important; this is called “ecological time”. But humans likely do not notice the
changes in the forest, since these changes are too small and take place too tacitly
for human perception. However, it is necessary to synchronize human activities
with the natural cycles within the forest ecosystem, otherwise the community
might run out of resources. The third timescale directly regulates the synchronization
of human activities. Equivalents of these timescales can be found in historical
theories and may be addressed as longue durée, durée structurelle, or histoire evenementielle
respectively.
In cities, humans became more and more decoupled from ecological time and
seasonal variations, as variations in climate and nutrient flows are diminished and
access to energy and matter is stabilized. The necessity of coordinating peoples in
towns generates and favors systems of time measurement to synchronize human
activities effectively. However, the consequences of human activities (e.g. the
economy, management of natural sources, warfare) certainly affect the material
basis for the long-term persistence of cities, which is nothing but the influence on
the ecological time of the ecosystem “city” by its own inhabitants.
2.7 Comparative summary
Cities are ecosystems, but in contrast to other ecosystems, they do not emerge by
themselves and they are unable to maintain themselves, they are therefore not
autopoietic systems in terms of self-reproduction. The ecosystemic character of a
city applies to abiotic features (soil, water, climate) and biotic features (humans,
plants, animals). These factors are linked by energy and material flows and build a