Urban and economic
systems can not be fully understood in isolation from their resource
base ¡V the ecological system within which they exist. Cities have to
rely on the ecosystem beyond the city limits and maintain stable links
with the hinterland from which they draw energy, food, and materials and
into which they release their wastes.
Ecosystem services refer
to the benefits of human beings derived from ecosystem function.
According to de Groot (2006), ecosystems can serve five primary
functions: regulation functions provide and maintain the conditions for
life on Earth and often provide the necessary pre-conditions for all
other functions; habitat functions relate to the spatial conditions
needed to maintain biotic and genetic diversity and evolutionary
processes, based on different species and the physical aspects of the
ecological niche within the biosphere; production functions provides
resources for human use, ranging from food and raw materials to energy
resources and genetic material; information functions are an ¡§reference
function¡¨ and reflect ecosystem services providing opportunities to
humans; and the capacity of natural system can provide carrier functions
for humans¡¦ activities and requirements limitedly.
Monetary valuation of
ecosystem services and natural capital may be useful to demonstrate
their economic value but is insufficient to measure the intrinsic worth
of the life support function of ecosystem (Costanza et al., 1997). The
intrinsic value of the natural environment in providing life-support
services requires a new accounting system that can assure the
contribution of non-marketed natural environment to the economic system.
Energy flows are not only one of the most important unifying concepts in
ecosystem development they are also the only common measure that
connects ecosystems and economic systems (Hall et al., 1986).
Biophysically based energy analysis can provide a comprehensive
framework to analyze urban ecological economic systems that allows
non-market information to be incorporated more easily.
In order to evaluate the
contributory value of different material flows to the ecological
economic system, Odum has formulated a unifying theory of system ecology
of values (Odum, 1971, 1988, 1996) and introduced the concept of emergy.
Emergy is defined as all the available energy that was used in the work
of making a product in units of one type of energy (Odum, 1996). The
energy content (e.g. joule) or mass of a flow can be multiplied by its
solar transformity to obtain its solar emergy in solar emergy joules (sej).
Emergy indices can be developed to evaluate the work of nature and their
contribution to urban systems. Further details on the concept and
procedure of emergy synthesis can be found in Huang and Odum (1991),
Odum (1996), and Brown and Ulgiati (2004).
M. T. and S. Ulgiati. (2004). Emergy and environmental accounting. In:
Cleveland, C. (Ed), Encyclopedia of Energy. Vol.2. pp. 329-353.
R., d¡¦Arge, R., Groot, R. d., Faber, S., Grasso, M., Hannon, B.,
Limburg, K., Naeem, S., O¡¦Neill, R. V., Paruelo, J., Raskin, R. G.,
Sutton, P., and Belt, M. v. D., (1997). The value of the world¡¦s ecosystem
services and natural capital,
Groot, R. S. (2006), Function-analysis and valuation as a tool to assess
land use conflicts in planning for sustainable, multi-functional
landscapes, Landscape and Urban Planning, 75: 175-186.
C. A. S., C. J. Cleveland, and R. Kauffmann.
Energy and Resource
Quality: The Ecology of the Economic Process. New York: John Wiley and
S. ¡VL. and H. T. Odum. (1991). Ecology and economy: Emergy synthesis and
public policy in Taiwan, Journal of Environmental Management, 32:
H. T. (1971).
Environment, power and society. New York: John Wiley and
H. T. (1988). Self-organization, transformity, and information,
Environmental Accounting. New York: John Wiley.