The city as disturbance of the local ecosystems - ESEE 2011 ...

ISEE2011 – "Advancing Ecological Economics – Theory and Practice”. The 9th International
Conference of the European Society of Ecological Economics, 14-17 June 2011, Istanbul
The city as disturbance of the local ecosystems
Ioan M. Ciumasu, Keith Culver
'Econoving' International Chair in Eco-Innovation, University of Versailles Saint Quentin-en-
Yvelines, Versailles, France. Contact: ioan.ciumasu@uvsq.fr, +33-139-255163.
Abstract
This paper makes a synthesis of the current ecological theories that are relevant to
biodiversity conservation, and applies it the the concept of city as a concentrator of resources
from a natural hinterland. Most notably, the paper discusses the intermediate disturbance
hypothesis (IDH) and the island biogeography theory, both well known in the ecological
literature to identify a typology of cities, with respect to their sustainable/unsustainable
character. In this context, the paper shows that cities can be classified according to the
features of urban biodiversity. This new typology builds on the existing taxonomical efforts
upon ecosystem goods and services and on the types of socio-ecological systems and human
nature relations. The managerial aspects are being discussed onto this new framework, and the
relevance for managerial practicess and business. For in-depth analysis, public green spaces
are being used as examples of application, and some new types of business asociated to it.
Keywords: urban ecology, ecosystem services, intermediate disturbance, island biogeography
Introduction
Urban ecology is a rather recent field of research. Its recent development reflects the gradual
acceptence of the fact that human settlements – typically seen as artificial environment – are
embedded in the natural context, as part of it and not just surrounded by it.
These developments seems to converge with the systemic view of sustainable development,
according to which any socio-economic system is part of a natural system (Giddings et al.,
2002). The systemic conception grounds the development of a necessarily transdisciplinary
approach to sustainability, as it is currently laboured within the field of ecological economics,
with strong social emphasis in recent years (e.g., Ropke, 2005; Gowdy & Erickson, 2005;
Spash, 2011). Furthermore, the systemic view seems to provide a framework for the
development of policy options for new technological developments (Musango & Brent, 2011)
and urban management scenarios (Ciumasu et al., 2011). In addition, the notion of urban
ecological footprint has been developped as economical tool capable to assist urban and
regional planning (Wackernagel et al., 2006; Moos et al., 2006).
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However, urban ecology is a very new sub-discipline. Despite signs of convergence towards
the synthetic effort of ecological economics and sustaianbility studies, itself a new endeavour,
it is highly uncertain on which bases the connection will be made between the two. For
example, since the beginning of the 21st century, cities are being regarded as knowledge and
technology hubs and socio-economic engines, both individually and within a global urban
network (Beaverstock et al., 2000). We also know that "nature in the city” (most notably
green spaces) is a meaningful issue, as reflected in the efforts on urban ecosystem goods and
services (Bolund & Hunhammar, 1999). But what is actually the place of the city from an
ecological perspective?
Urban ecology can be defined as „the interaction of social and ecological systems within
urbanized space and the impact such interactions have on external systems” (Young, 2009).
As such, within the environment, the city has a clearly identifiable identity, a set of features
that makes it a socio-ecological system and thence distinguishes it from the surrounding
environement. The question now is: How does this social-ecological system, in deed a colony
of our species, fit within the wider ecological systems? What is, ecologically speaking, this
Homo sapiens’ colony called "city”? This is the concern of the present communication, which
attempts to provide some theoretical ground for future answers.
Proposed conceptual approach
On the grounds of current ecological theory, the folowing hypothesis can be formulated/used:
Within a given ecosystem or continuum of ecosystems, any given city is a disturbance. The
term 'disturbance' is used with its ecological meaning of perturbation of ecologically
describable ecosystem dynamics. As the factor of this disturbance is obviously the presence of
the species Homo sapience in a locally high density of individuals, the city becomes the most
prominent case of the wider situation of the occurence of human settlements (colonies, from
an ecological perspective). The hypothesis can bear a generalized form – Within a given
ecosystem or continuum of ecosystems, any given human settlement (or colony) is a
disturbance – and should be treated as such from an ecological theoretical perspective.
Results – theoretical consequences
A major path to understand ecosystems structure and function (and ultimately ecosystem
services) is via biodiversity proxies. To date, there exist no unified biodiversity theory of
biodiversity, but several major theories are enduringly successful in predicting a large amount
of patterns found in nature. One is the classical equilibrium theory of Island Biogeography
(IB), stating that biodiversity in a given teritory (originally illustated by islands in the
planetary ocean) is a direct result of the dynamic equilibrium between the immigation of new
species and the extinction of the species already present there, which in turn depend on
physical distances and local ecological processes like competition between species
(MacArthur & Wilson, 1967; Simberloff, 1974; Kadmon & Allouche, 2007). Another is the
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Intermediate Disturbance Hypothesis (IDH), a line of thought stating that, at a given location,
the highest levels of biodiversity occur at intermediate levels (intensity and frequency) of
disturbance. This phenomenon has been observed empirically but is hard to test, since it can
result from very different processes (Wilson, 1990; Roxburgh et al., 2004). The two theories
complete each other, IB being more useful for large scale patterns and IDH at local scales.
Given the both global and local relevance of cities, the two ecological theories need to be
taken into account when trying to understand the relation between a city and ecosystems. By
regarding a given city (or a human settlement in general) as a disturbance, it immediately
follows that (i) cities of various sizes may have interestingly different impacts on ecosystems,
and (ii) that the ranges of these impacts are being determined by the position of the city within
the continental and global biogeography. The first point identifies the local ecological issue,
and constitutes the focus of this papers, while the second defines its ecological context.
Notably, point (i) implies the existence of three categories of human settlements (HS),
corresponding to the three levels of disturbance intensity according to IDH: low, intermediate
and high. At the level of geological time, three categories can be identified, though less
intuitive, correspondig to the disturbance frequency: low, intermediate, and high. For
simplicity purposes, this communication will focus on the intensity, but the time is still taken
into account, as the simple duration of the disturbance (in social terms, the lifetime of a city).
For cities, these categories can be observed both at the level of city units (a big city generates
a big impact) and at the level of disturbance intensity on a gradient from city perifery to city
centre (Table 1). This typology does not indicate what the absolute value of the disturbance
intensity is, but it also does not need to, since this vary with context and can be identified at a
latter stage for management purposes, as applied to a chosen city. However, the typology
points out to the existence of a natural taxonomy of urban areas (as socio-economic systems)
with respect to their ecological place in the natural system into which they are embedded,
according to the systemic view on the sustainability of human activity on Earth.
A typology of management objectives is also identifiable, as to account for the different
ecological impact that periferic and central areas may have on ecosystems. Also, the typology
allows for natural (ecologically-relevant) boundaries to be established between periferic, nearcentral
and central areas of a city, in relation to the local set of ecological constraints and
limitations.
Table 1 – Typology of urban areas, as derived from the IDH
Disturbance intensity City unit City area (on a centrifugal axis)
low small city city perifery
intermediate medium size city city near-central
high large city city centre
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Further, for any city (urban unit), the ecological profile can be described on a managementrelevant
gradient of disturbance intensity. Thus, during the life span of a city (the century or
the decade can be used as relevant time units), its impact upon the environment varies: it first
goes through a period of increasing impact, then it experiences a period of maximum impact,
and then enters a period of decreasing impact. From the socio-economic perspective, these
stages can be described as the rising period, the golden age, and the decline. In this case, the
environmental impact varies proportionally with the socio-economic development, and can be
therefore considered a proxy for city life stages. Thus, socio-economic success is just
indicated by how much water is extracted, how much wood is burned, or similar measures
that can be understood as indicators of economic activity.
Now, the most interesting part of this evolution is the peak that corresponds to the golden age
in a city’s lifetime. Figure 1 illustrates five theoretical categories of disturbance intensity. For
the sake of conceptual clarity, necessary for this introduction to the concept, the city lifespan
is considered to be identical in all cases, thence the symetrical trajectories of the disturbance
intensities.
Disturbance intensity [d]
5
4
3
2
1
0
0 2 4 6 8 10 12 14 16
City life time [t]
Figure 1 – Typology of cities’ lifetime, as derived from the IDH and the concept of ecosystem
carrying capacity. Disturbance intensity d1 corresponds to the ecological carrying capacity
that is available to a city, correponding to a critical "no return point" meaning a threshold
which, if crossed, triggers a decrease of the absolute value of the ecosystem carrying
capacity. If not crossed, the respective carrying capacity is regenerable. Further, d2, d3, d4
correspond to the level where a city has already engaged on a path of degradation of the
carrying capcity available to it, but the speed of that degradation can be accelerated once
varios thresholds are being crossed.
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Discussions – consequences for urban planning
When local factors and measures are factored in, the concept described above allow definition
and quantification of important parameters like city resilience and vulnerability. This also
alows a more structured discussion on the role of cities in the transition to sustainability.
Cities cannot be sustainable per se, but only within the wider hinterland. On the one hand, this
is why IB theory becomes important with the size of the hinterland. On the other hand, this is
why the concept of eco-city is more appropriate in the discussion between urban areas and
transition to sustainability. It is not possible to decide whether a city is sustainable or not.
Instead, measures can be found to estimate how close it is to the objective of sustainability.
Various urban ecological measures can be used as proxies and indicators of the variation of
the disturbance intensity by/in urban areas, like urban biodiversity indicators or energetic
measures related to the urban heat island effect. In this context, progress in the transition to
sustainability through innovative and integrative techno-social-economic-ecologic-managerial
actions will not be measured in absolute terms (it would not be possible), but in the relative
terms of progress from one level of city impact upon the environment to the lesser one. In this
case, innovation is eco-innovation, the innovation process which results in lesser impact of
human activities upon the environment.
In this context, a provision is germane to the role of urban green areas, as this is one major
avenue of "greening" the cities. The dynamic of green spaces in European cities appear to be
more correlated with city surface size than with population density, signalling a continuing
compaction of urban areas in the future (Fuller & Gaston, 2009). If city compaction will
continue, as it seems, the impact of the city opon ecosystems outside the city perimeter will
increase. Rather than understanding future cities in terms of green areas per inhabitant within
the perimeter of a city, urban management will have to consider (1) the ecological role of the
city within its hinterland (and, as a hub of a global network of cities, also as part of the
bioshpere) according to an ecologically relevant typology and dynamics, and (2), the spatial
structure of the city along a centre-perifery axis.
The concept presented hereby allows apt managerial links to notions of ecological footprint,
carrying capacity, and urban 'optimization' and fitting modes of living to environments. It may
be especially interesting to consider this approach as a general theoretical ground which will
enable a more reflective assessment of just what kind of density of inhabitants is appropriate
to what kind of city and ecosystem service. The zest for one-size-fits-all futuristic projects
risks obscuring or impairing careful thinking about the diverse ways in which cities of the
future might be structured in light of their particular ecological locations, links to trade routes
with specific ecological services and values and costs, and related factors.
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