Illinois Natural History Survey - University of Illinois

Cities and Ecological Dependence

A basic ecological problem of cities (as opposed to problems in cities) is their dependence beyond their borders for energy, water, minerals, food, and other necessities, and for assimilation of their wastes. The "sustainable city unit" therefore should include not just the acreage of cities and their suburbs but also the ecologically productive land anywhere on the globe that support it. "Ecological Footprint," developed by planners Mathis Wackernagel and William Rees at the University of British Columbia, is a vivid descriptor of this dependence.

Such footprint calculations, though based on many arguable assumptions, indicate that at urban, national, and global scales, humans have ecological footprints exceeding available land. The ratio of footprint to actual area is of order 100 for industrialized cities, 10 for developed countries (notable exceptions: Canada and Australia, which, though rich, are sparsely populated), and 2-3 for the entire human race.

Unless wildly incorrect, these results imply that present activity is unsustainable and that we are likely in an overshoot period preceding a decline in productive life-support. Given that there are now worldwide 345 cities of more than a million inhabitants, with 527 projected in 2015, this growth is dire. Yet it also offers impetus to design and execute more sustainable societies, and the details offer points of improvement (particularly in water and energy). Typically the issue of dependence in a finite world is the last bastion of denial about human impacts. Acting locally to address the larger problem is difficult, as planners will admit. If dependence were a serious factor in urban planning, cities could have smaller footprints, and the sizes and distribution of urban concentrations would be different. In economic terms, city life would cost more than it does today, and the urbanization trend would not be as rapid.

Dependence, along with depletion (of resources) and disturbance (of natural flows and cycles) comprise the 3 Ds, a set of indicators Todd Wildermuth and I use to evaluate the environmental sustainability of agricultural practices and agriculture-based communities in Illinois and Kansas. In Chase County, KS, we find, not surprisingly, that in terms of energy and nitrogen, land used for raising range-fed beef has lower dependence than land in row crops, as shown in Table 1. 


Table 1. Summary chart of indicators for Chase County, KS soil, water, energy, and nitrogen resources. Depletion is the ratio of the drawdown rate divided by the stock and has the units of 1/time. The inverse is the static lifetime: how long nonrenewable resources will last at today's deletion rate. Disturbance is (today's flow)/("natural" flow) - 1. Dependence is import/internal use. All three D's are thus 0 for the nondepleting, undisturbed, independent ("self-sufficient") case.

A. Soil includes only the A horizon, which is treated as a homogeneous unit.

B. Grazed land includes range, pasture, and grazed forest. Ungrazed land includes row-cropland and towns.

C. Given as a range due to the uncertainty in rates of soil formation.

D. Given as a range due to the uncertainty in fixation by prairie vegetation.

E. Details of long-term nitrogen cycling are unknown.

F. Assumes the same stock of nitrogen as grazed lands.

In addition, Chase County exports crude oil and natural gas, yet imports all the refined petroleum and natural and bottled gas it burns, and hence has both high depletion and dependence for energy.

I am now designing research with planning faculty members to calculate, and to use in actual planning practice, these indicators for smaller Illinois cities. The typical question is how more efficient use within the city will reduce beyond-boundary requirements. This includes use of water and energy, recycling of packaging, design of buildings and transportation systems, promotion of local agriculture, and provision of green space.

Robert A. Herendeen, Center for Aquatic Ecology

Charlie Warwick, editor

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