Ecological Footprint Wackernagel and Reesgradient Analysis

Ecological Footprint Wackernagel and Reesgradient Analysis

Landscape Ecology
Landscapes of the future, and future directions for landscape ecology

Terms/people:

"ecological footprint"Wackernagel and Reesgradient analysis

coalescence urban ecosystem biotic homogenization

urban heat island

Questions for students to answer BEFORE coming to class:

What was the largest city in the world in the year 1700? ______

What is the largest city today?______

By the year 1800, only 1 city in the world had more than 1 million inhabitants. By the year 2000, 388 did.

Urban landscapes have traditionally been seen as being the antithesis to “natural” (i.e., pristine) landscapes. This gradient from trashed to pristine landscapes was also seen as a gradient of human influence. Urban landscapes were thus considered to be abnormal (even diseased) and thus unlikely to provide new insights into how nature works. They were thus ignored until quite recently. Now, however, urban pattern-process relationships are considered worthy of study because urbanization effectively creates a new type of landscape, with unique pattern-process relationships: an urban ecosystem. Although much of the Earth’s human population lives in urban settings (and this proportion is growing through a sociological process called coalescence whereby small towns lose population to a nearby larger urban site), urban areas occupy relatively little of the Earth’s surface area (~2%). However, urban systems are characterized as producing effects that are disproportionate to their spatial extent.

General traits of urban ecosystems/landscapes:

- presence of a heterogeneous spatiotemporal mosaic whose effects extend far beyond obvious development per se (“ecological footprint,” more below)

- much higher energy consumption/input vs. other ecosystems

- lower biodiversity but higher abundance/dominance of certain species

- homogenization of biota (rats, pigeons, starlings, House Sparrows, and other synanthropic spp.) - see McKinney 2006

- species replacements (esp. exotics replacing natives)

- alteration in patch characteristics and dynamics with degree of urbanization (Luck and Wu 2002): urban areas are characterized as having different spatial properties, compared to non-urban areas (e.g. urban areas exhibit higher edge density and a more variable number of patches)

- presence of altered biogeochemical cycles (usually high N deposition, heavy metals, etc. from pollution, fertilization, soil compaction)

- "urban heat island" effect -

- urbanization is occurring mainly on former cropland, so an increase in urbanization usually means a concomitant decrease in agricultural land; this means that more food (for a burgeoning population) must be grown on marginal land, which usually necessitates agricultural intensification

Note that these traits consist of inputs and outputs to the urban system. These inputs and outputs are collectively called an "ecological footprint" (Wackernagel and Rees 1995). The ecological footprint is an accounting tool for ecological resources. Categories of human consumption are translated into areas of productive land required to provide resources and assimilate waste products. The ecological footprint is a measure of how sustainable our life-styles are. You can take a quick and easy on-line quiz at to see how big your own personal footprint is. It is sobering. You will see just how much land is required for food, housing, transportation, consumer goods, and services to support your lifestyle. Obviously, the bigger your footprint, the more resources you are consuming.

Urban systems have large but variably sized footprints, depending on their water, food, and fossil fuel consumption (and from where those items come), availability of public transportation, and infrastructure for communication and provision of goods and services.

So how do we minimize the urban footprint?

First, we have to be able to study and quantify the system and its effects.

The most common approach to studying urban ecosystems is a form of a standard approach taken to studying "natural" ecosystems: gradient analysis. Use of gradients has been a firm tradition in ecology, particularly plant ecology (Whittaker 1967). In gradient analysis, some environmental variable (e.g. soil N, salinity, soil moisture) is measured along a gradient from high to low areas of concentration. The plant community (diversity, density, physiological characteristics) is also measured along this gradient, and spatial patterns are correlated to each other. In studying effects of urbanization, the gradient is one of urban development. For example, Godron and Forman (1983) described a "landscape modification" gradient consisting of urban to suburban to cultivated to managed to natural (decreasing level of human dominance). McDonnell and Pickett (1990) took such an approach to describing an urban-rural gradient from New York City to rural Litchfield County, CT, to study how urbanization (proximity to urban) affects landscape structure and function (e.g. litter decomposition, biodiversity, etc.). Although gradient analysis is not perfect (esp. for cities with leapfrog development or multiple urban cores), it is a way of quantifying effects of urbanization in a spatial way.

Once the system is described, then the negative effects can be identified, and the necessary resources allocated to either remediate current negative effects or to prevent future negative effects. The disciplines of landscape architecture and land-use planning are devoted to these pursuits. I leave further details to courses in these departments on campus, but urban landscape ecology can fuse the North American and European schools of LE.

You, personally, can minimize your own footprint size by using public transportation, using local products, consuming less processed/pre-packaged foods, and using energy-saving devices such as solar-powered water heaters or energy-efficient light bulbs.

For more info about current research into urban ecology, check out the Central Arizona-Phoenix Long-Term Ecological Research site, and the Baltimore Ecosystem Study Long-Term Ecological Research site,

Landscape ecology has been called a "science in search of itself" (Hobbs 1994) because of its youth, variety of roots, and multitude of approaches, all of which suggest a lack of focus and unique identity. More recently, however, Wu and Hobbs (2007) make a compelling argument against this criticism and show how landscape ecology's multidisciplinary nature provides a framework for obtaining a holistic understanding that a single-disciplinary approach cannot provide. In this sense, landscape ecology has changed how ecologists view the world.

What has landscape ecology brought to ecology as a whole?
1) Recognition that pattern and process are interdependent.
2) Acknowledgment that habitat amount, isolation, and configuration are all influential. Recognition that habitat configuration (context) is important is a particularly important contribution from landscape ecology.
3) Recognition that pattern-process relationships are scale-dependent.

Some potentially fruitful areas for future research in landscape ecology:
- Since the vast majority of ecological studies are based on small-scale studies with limited empirical support but are used to create and support global models, there is an obvious need to reconcile these two scales. Landscape ecological approaches may be useful in this endeavor.
- Thresholds, nonlinearities, and scaling laws have yet to be worked out for most situations.
- Ameliorating the consequences of human land-use change is an accelerating need.
- Empirical evidence is needed for how habitat context and configuration influence long-term population viability and biodiversity conservation.

- Habitat fragmentation via global climate change is subtle and insidious. An estimated 15-37% of species on Earth will become threatened by global climate change by the year 2050 (Burns et al. 2003).

- Landscape genetics: study of how environmental features influence population genetic structure; how spatial pattern affects processes of natural selection, gene flow, and drift (Manel et al. 2003, Holderegger and Wagner 2006)

Isolation by distance being replaced by “isolation by resistance”

Landscape Ecology volume 21 (2006) has a special feature on this topic.

Manel, S., M.K. Schwartz, G. Luikart, and P. Taberlet. 2003. Landscape genetics: Combining landscape ecology and population genetics. Trends in Ecology and Evolution 18:189-197.

Hoderegger, R., U. Kamm, and F. Gugerli. 2006. Adaptive vs. neutral genetic diversity: implications for landscape genetics. Landscape Ecology 21:797-807. [Introduction to genetic analyses that are most relevant to landscape ecology.]

Storfer, A., M.A. Murphy, J.S. Evans, C.S. Goldberg, S. Robinson, S.F. Spear, R. Dezzani, E. Delmelle, L. Vierling, and L.P. Watts. 2007. Putting the ‘landscape’ in landscape genetics. Heredity 98:128-142.

-Landscape epidemiology: study of how environmental pattern affects the emergence and spread of disease

Ostfeld, R.S., G.E. Glass, and F. Keesing. 2006. Spatial epidemiology: An emerging (or re-emerging) discipline. Trends in Ecology and Evolution 20:328-336.

Holdenrieder, O., M. Pautasso, P.J. Weisberg and D. Lonsdale. 2004. Tree diseases and landscape processes: the challenge of landscape pathology. Trends in Ecology and Evolution 19:446-452.

Plantegenest, M., C. Le May, and F. Fabre. 2007. Landscape epidemiology of plant diseases. J. R. Soc. Interface 4:963-972.

Despommier, D., B.R. Ellis, and B.A. Wilcox. 2006. The role of ecotones in emerging infectious diseases. Ecohealth 3:281-289.

Brownstein, J.S., D.K. Skelly, T.R. Holford, and D. Fish. 2005. Forest fragmentation predicts local scale heterogeneity of Lyme disease risk. Oecologia 146:469-475.

Jackson, L.E., E.D. Hilborn, and J.C. Thomas. 2006. Towards landscape design guidelines for reducing Lyme disease risk. International Journal of Epidemiology 35:315-322.

Landscapes have been changing since the world began and will continue to do so (with or without human witnesses). Therefore, there will always be and interest in how spatial patterns influence biological processes (and the converse).

References:

Burns, C.E., K.M. Johnston, and O.J. Schmitz. 2003. Global climate change and mammalian species diversity in U.S. national parks. PNAS 100:11474-11477.

Fortin, M-J and A. A. Agrawal. 2005. Landscape ecology comes of age. Ecology 86:1965–1966.

Godron, M., and R.T.T. Forman. 1983. Landscape modification and changing ecological characteristics. Pp. 12-28 in: Disturbance and Ecosystems: Components of Response (H.A. Mooney and M. Godron, eds.). Springer-Verlag, New York, NY.

Hobbs, R.J. 1994. Landscape ecology and conservation: moving from description to application. Pacific Conserv. Biol. 1:170-176.

Hobbs, R.J. 1997. Future landscapes and the future of landscape ecology. Landscape and Urban Planning 37:1-9.

Holderegger, R., and H. Wagner. 2006. A brief guide to landscape genetics. Landscape Ecology 21:793-796.

Hopkins, L. 2001. Urban Development: The Logic of Making Plans. Island Press, Washington, D.C.

Luck, M., and J. Wu. 2002. A gradient analysis of urban landscape pattern: a case study from the Phoenix metropolitan region, Arizona, USA. Landsc. Ecol. 17:327-339.

Manel, S., M.K. Schwartz, G. Luikart, and P. Taberlet. 2003. Landscape genetics: combining landscape ecology and population genetics. Trends in Ecology and Evolution 18:189-197.

McDonnell, M.J., and S.T.A. Pickett. 1990. Ecosystem structure and function along urban-rural gradients: an unexploited opportunity for ecology. Ecology 71:1232-1237.

McIntyre, N.E., K. KnowlesYánez, and D. Hope. 2000. Urban ecology as an interdisciplinary field: differences in the use of "urban" between the social and natural sciences. Urban Ecosystems 4:524.

McKinney, M.L. 2006. Urbanization as a major cause of biotic homogenization. Biol. Conserv. 127:247-260. [A nice review paper from "Mr. biotic homogenization."]

van den Bergh, J.C.J.M., and H. Verbruggen. 1999. Spatial sustainability, trade and indicators: an evaluation of the 'ecological footprint'. Ecological Economics 29:61-72. [A critical review of the ecological footprint concept; see also the March 2000 issue of Ecological Economics for an entire forum on ecological footprints.]

Wackernagel, M., and W. Rees. 1995. Our Ecological Footprint: Reducing Human Impact on the Earth. New Society Pub., Philadelphia, PA.

Whittaker, R.H. 1967. Gradient analysis of vegetation. Biological Review 49:207-264.

Wu, J., and R.J. Hobbs, eds. 2007. Key Topics in Landscape Ecology. CambridgeUniv. Press, Cambridge, UK.