Urban ecology

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The term urban ecology (or the English equivalent of urban ecology ) describes a number of different approaches in the area of ​​tension between city and ecology .

1. The exploration of urban habitats using the approaches and methods of ecological research. Urban ecology in this context means the investigation of habitats and biotope types that occur specifically in cities, especially urban spontaneous flora or vegetation and fauna. Humans and human influences occur in connection with the specific location factors, but are not themselves the subject of research. Applications exist in relation to green planning and design in cities, to nature and nature experience as well as to nature conservation of urban habitats.

2. the exploration of cities as ecosystems , d. H. the consideration of entire cities with the approaches and methods of synecology and ecosystem research. In particular, in the context of ecosystem research, determination of the energy and material flows and balances of entire cities. A popular concept to illustrate the approach is an “ ecological footprint ” of a city.

3. In the context of urban planning and development: The goal of an “ecological” or “sustainable” city, in particular to reduce land and energy consumption and to create livable urban districts. Urban ecology in this sense is an applied social science that strives for ecologically defined goals, but has nothing to do directly with the methods and research programs of ecology (as a biological sub-discipline).

4. A previously influential branch of research within sociology (the “ Chicago School ”) that applied ecological research methods directly to the study of sociological phenomena in cities (“ social ecology ”).

Related and overlapping fields of research are landscape ecology , human ecology and civilization ecology .

Abiotic Aspects

Cities have a number of peculiarities in all natural living conditions compared to their surrounding areas, e.g. B. in the climate (cf. urban climate ). These change the living conditions not only for flora and fauna in general, but also for the people who live here.

Change in the radiation budget

The global radiation is reduced in cities due to increased turbidity of the air. Selective filtering of the short wavelengths (particularly strong: UV ) results in a red shift. Since the back radiation is increased due to the cloudiness of the air and multiple reflections on buildings, the heat radiation is increased despite the reduced global radiation. The building materials generally have a lower albedo than vegetation (average value approx. 0.15, thus in the short-wave approx. 10% lower) and can therefore heat up more when exposed to radiation. Stones have a high heat capacity, which means that cities warm up more slowly in the morning, but do not cool down as much at night. The anthropogenic heat development through combustion processes can reach the same order of magnitude as solar radiation, at least in winter.

Change in atmospheric chemistry

In cities, the pollution from fine dust is many times higher than in the surrounding area. As a result, in addition to the direct consequences, radiation (via air turbidity) and water balance (via the influence of condensation germs) are changed. Many pollutants such as B. Cadmium as a component of the dust pollution in cities are significantly increased, they increase (after their deposition) the content in the topsoil. In contrast, the ozone content is lower because it is only formed by atmospheric chemical reactions away from the emitter . The amount of carbon dioxide in the city air is greatly increased.

Change in the water balance

Due to the low vegetation cover, the transpiration of which is lost, a much smaller part of the precipitation evaporates in cities than in the surrounding area. Most of the water is directed into the sewer system via the large area of ​​the buildings, streets and other paved areas, thereby increasing surface runoff in the bodies of water into which it discharges. The formation of new groundwater remains almost unaffected in moderately sealed urban districts, it only sinks in the heavily dense center. In cities, however, the groundwater level is usually lowered due to the influence of the sewer system (which acts as surface drainage). Although the air humidity is lower because of the lower level of evaporation, fog formation occurs more frequently because of the exposure to dust, which acts as condensation nuclei.

Urban climate

In the complex interplay of these factors, a. to the following effects:

  • The average temperature in densely populated cities is higher than the surrounding area by an average of 0.5 to 1.5 ° C (urban heat island). In addition to the heat reflection, the failure of heat transport due to the reduced evaporation plays a decisive role. The effect is hardly noticeable in green suburbs.
  • Cities create a small, local low pressure area due to the rising heated air and the wind field (updrafts) deflected upwards by the tall buildings. As a result, it rains more in cities than in the surrounding areas, and the sky is clearly (approx. 5–10%) more cloudy.
  • The average wind speed in cities is reduced by the effect of the buildings compared to the open field. Unlike z. B. in forests but there is increased turbulence. In narrow street canyons with tall buildings there can be uncomfortably increased gusts due to the jet effect.

City floors

The floors in cities, despite the increased precipitation significantly drier than the surrounding area. In addition to a lowering of the groundwater level through drainage and surface sealing, soil application leads to an increased distance from the groundwater to the surface. In addition, the mostly increased sand and gravel contents reduce the water retention capacity. Due to the heavy transport of building materials into the cities, urban soils very often consist of embankments without a natural soil structure . The pollution from the deposition of dusts and air pollutants can be so high that the limits of the Soil Protection Ordinance are exceeded in the topsoil and humus in urban forests . Soils in industrial and commercial areas are often interspersed with anthropogenic substrates such as building rubble, slag and ash and contaminated with operational and production-specific pollutants. Urban soils are often highly compacted and usually show nutrient imbalances, i.e. H. the contents of some nutrients are greatly increased, those of others are reduced. Concrete and mortar dust has usually shifted the pH value of urban floors to an alkaline range. Extremely high pH values ​​can occur on blast furnace slag, which naturally cannot be reached in Central Europe, while an extremely acidic soil reaction occurs in the first few years on tailings from hard coal mining. Due to their mostly young development stage, application soils are often poor in humus, whereby the application and incorporation of carbonaceous substrates coke, coal or incompletely burned ash can result in relatively high carbon contents. High humus contents are characteristic of garden soils ( hortisols ), which are an independent soil type. Local changes lead e.g. B. de-icing salt on roads or natural gas leakage on leaking pipes.

Communities in cities

flora

Wall joint vegetation: Chelidonium majus

For plant species that live in cities, the above-mentioned changes in location and local climate are of course limiting factors. However, other factors are even more important. The flora of the cities can be characterized by:

  • Heterogeneity: Cities, especially the areas outside of the highly sealed and hostile centers, offer a multitude of different locations in a very small space. Although natural and agricultural habitats are also heterogeneous, urban habitat mosaics have proven to be more diverse and small-scale. Cities typically have fragments of natural habitats, mixed with gardens, parks and green spaces , hems , fallow and green separators , which all have their characteristic species equipment.
  • Dynamics: Urban living spaces are typically often disturbed and short-lived. In addition to recurring disruptions such as foot traffic, changes of use, complete destruction of the vegetation cover, possibly followed by periods of rest for decades, are possible at any time. Species that depend on habitat continuity and undisturbed habitats with a long development time are therefore lacking.
  • Rapid species change: In cities, the constant flow of material means that the seeds of plant species are constantly being introduced. Thousands of species are deliberately planted and cultivated in gardens and green spaces, some of which can survive in the wild, including both introduced species ( neophytes ), which are particularly common in cities, as well as indigenous species.

As a result, the (spontaneous, wild-growing) flora of almost all cities examined tends to be somewhat more species-rich than that of the surrounding areas. In addition, the larger the city, the higher the number of species. However, this biodiversity is not evenly distributed over the entire flora. The vegetation of the cities is predominantly short-lived Ruderalfluren nitrogen needy Hochstaudenfluren constructed various meadows and grassland communities and bushes and Vorwäldern. In dense urban, there are most likely to enter permanent adapted kick companies and Ritzen- and wall joints vegetation. Types of other vegetation units, such as In cities, for example, near-natural forests, swamps , bogs and grasslands rarely find opportunities to live; they avoid cities (“urbanophobic” in the sense of Wittig ).

For a detailed comparison, the results of Chocholousková and Pysek from Pilsen , a medium-sized Czech industrial city with approx. 170,000 inhabitants, are interesting, from which three temporally separated studies (around 1900 around 1970, around 1990) are available. They observed the following: The number of species in the city has increased significantly during this time (478, 595, 773 species). At the same time, the number of species in the surrounding area has fallen sharply (1112, 768, 745 species), so that overall (city and surrounding area together) the number of species has fallen by a good 10%. The proportion of constantly recorded species was only 57%, with the species change in the city being much higher. The proportion of neophytes has risen sharply in the city (from 6.2% to 17%), while it has remained almost constant in the surrounding area. That means: The species distribution in the city has changed drastically, around 30–40% of the indigenous species have been replaced by new immigrants. Due to overgrown cultivated trees and shrubs, the number of woody plants in the city has increased from 26 (including 2 neophytes) to 117 (including 33 neophytes). Similar changes can be assumed for numerous central European cities. So is z. For example, the total number of species in Bochum (Ruhr area, North Rhine-Westphalia) is higher today than in 1887 and the proportion of naturalized neophytes has risen from 4% to 16% since then.

Extensive lawns are an important type of vegetation in cities . Lawn is a characteristic element, especially in suburban residential areas, where public and private lawns can almost always take up more than 10%, sometimes even more than 25% of the floor space. Individual lawns are usually made up of 15 to 20 plant species, with the (sown, but also spontaneous) grasses dominating the cover, the herb species dominating the number of species. Since lawns have typical and distinctive plant species, e.g. B. Small brown ella or stiff-haired dandelion , they can be described as plant communities according to the plant-sociological system. While the flora of the lawn corresponds to that of fertilized meadows, its fauna is extremely species-poor. The maintenance of lawns has become proverbial as a preoccupation for middle-class suburbanites and is used as a cliché in numerous jokes. U.S. citizens spent about $ 8.9 billion on lawn maintenance in 1999. Studies on the sociology of turf have also been studied in the USA, but are easily transferable. According to interviews, suburban homeowners associate the condition of the lawn with the moral character and social reliability of the residents. Lawn care serves the social security of the neighborhood, more intensive lawn care workers were more likely to know their neighbors by name: the condition of the lawn serves as a public statement and is perceived as such. The importance of lawns and front gardens for social security and the deep-seated norms behind them were also shown in a study in South Africa. One of the downsides of these functions is the excessive consumption of fertilizers, pesticides and (especially in arid areas) water for lawn maintenance, which can exceed the consumption in agriculture.

fauna

Peregrine falcon on building (St John's Church, Bath, England)

Although several thousand animal species have been found in some of the better-researched cities, urban habitats are almost always significantly poorer in species than comparable ones in the surrounding area. This applies to almost all animal groups examined, from insects and small animals living on the ground to birds and mammals. Quite a number of species have adapted to urban conditions and are very common here. B. the total settlement density of breeding birds (with fewer species) in cities can be even higher. The fauna of larger green areas, e.g. B. parks with old trees or cemeteries , can be quite similar to the fauna of the surrounding area and offer a refuge for a number of species that actually avoid cities. In some studies, the well-examined breeding birds found the outskirts of the city to be more species-rich than the surrounding area or the center; in these cases, too, the number of specialized species fell from the surrounding area to the center. However, due to the addition of a species group that benefits from disturbances, the total number of species can initially increase.

What is particularly striking is a relatively small group of species that have been able to adapt well to urban conditions and are sometimes much more common here than in the surrounding area. This concerns z. B. the mammals rabbit , squirrel , red fox and stone marten and the bird species blackbird , turkey dove and house sparrow . More rarely than with flora, some wild animal species can also be traced back to feral captive refugees. The most common of these species is the city ​​pigeon , especially in parks there are other species such as mandarin duck , Canada goose , Egyptian goose or ring-necked parakeet. Almost only building-breeding species live in the city center, for which houses can serve as a kind of artificial breeding rock. In addition to sparrows and city pigeons, these include z. B. Common swifts , but for some decades also the peregrine falcon .

A special group of animal species was even able to conquer human buildings as habitat, one speaks of " synanthropic " species. In addition to house mice , house shrews and brown rats, they include numerous material and stored pests, but also harmless species such as z. B. the trembling spiders . However, these species occur wherever people live, so they are not more common in cities.

Functions

In addition to its independent value, nature in the cities also has functions for the people living here; one speaks of “ ecosystem services ”. The function of plants, especially trees, is particularly important. For this meaning, spontaneously grown and planted plants are in principle equivalent. As important functions are listed

The effect of parks, forests and tree-lined areas depends on their extent. Individual trees and small green areas improve the situation locally. Extensive forest-like stands can also influence the local climate in neighboring quarters.

On the history of urban ecology

One of the first indications of problems that are now assigned to urban ecology came from the English gardener Thomas Fairchild at the end of the 17th century. William Nylander (lichen flora of Paris 1866), Ferdinand Arnold (1891), Hans Höppner and others dealt with the flora and fauna of cities . Hans Preuss (1926), Richard Scheuermann , Kurt Wein and Louis Bonte with work on garden weeds in cities (1938) and (1930) on adventitious flora in cities.

For numerous studies on the vegetation of the debris flora , there were excellent study areas in Germany after the Second World War. In the second half of the twentieth century, numerous studies were also carried out on the abiotic factors of urban ecology. The term urban climate was coined by Albert Kratzer in 1937 , and the soils of a large city were first systematically examined in the mid-1980s by Hans-Peter Blume and Ralf Grenzius in Berlin.

In more recent times, the social and spatial science analysis shown has been increasingly taken into account and completes the previously primarily scientific approach.

Since 2002, within the framework of the DFG Graduate School 780 “Urban Ecological Perspectives” at HU, FU and TU Berlin as well as the IGB, a large number of doctoral and postdoc projects in the areas of urban, economic and cultural geography, environmental psychology and landscape ecology , soil science, hydrology, climatology, avifauna, plant ecology and remote sensing emerged. The German Research Foundation has thus contributed to the establishment and current further development of an interdisciplinary urban ecology at the science location Berlin. The last phase of the Research Training Group 2008 to 2011 was dedicated to the topic of "Optimizing urban nature development - natural functions and living environment in dynamic change".

See also

Web links

literature

  • AM Beck: The Ecology of Stray Dogs. A Study of Free-Ranging Urban Animals. Purdue University Press, West Lafayette 2002.
  • AR Berkowitz, CH Nilon, KS Hollweg (Ed.): Understanding Urban Ecosystems. Springer, New York 2003.
  • W. Endlicher: Introduction to urban ecology: basics of the urban human-environment system. Ulmer / UTB, Stuttgart 2012, ISBN 978-3-8252-3640-3 .
  • Günter Fellenberg: City as a living space. Verlag der Fachvereine, Zurich 1991.
  • SD Garber: The Urban Naturalist. Dover Publication, Mineola 1998.
  • OL Gilbert: Urban Ecosystems. Neumann Verlag, Radebeul 1989.
  • B. Klausnitzer: Urbanization of animals. Ziemsen, Wittenberg 1989.
  • B. Klausnitzer: Ecology of the big city fauna. Gustav Fischer, Jena 1993.
  • W. Meyer, G. Eilers, A. Schnapper: Garbage as a source of food for mammals and birds. Westarp Sciences, Hohenwarsleben 2003.
  • DW Orr: The Nature of Design. Ecology, Culture, and Human Intention. Oxford University, New York 2002.
  • K. Pezzoli: Human Settlements and Planning for Ecological Sustainability. The Case of Mexico City. MIT Press, Cambridge 1998.
  • JH Reichholf : The future of species. New ecological surprises. Beck, Munich 2005
  • H. Sukopp (ed.): Urban ecology. The example of Berlin. Reimer, Berlin, p. 1990.
  • C. Steinberg, B. Weigert, K. Möller, M. Jekel (eds.): Sustainable water management. Development of an evaluation and testing system. Schmidt, Berlin 2002.
  • H. Sukopp, R. Wittig (Ed.): Urban ecology - A textbook for study and practice. Gustav Fischer, Stuttgart 1998.
  • R. Wittig: settlement vegetation. Ulmer, Stuttgart 2002.
  • J.-M. Ehbauer: Possibilities of urban and building planning to support the wild fauna in the city. TH Karlsruhe, Karlsruhe 2004.

Individual evidence

  1. ↑ a b Till Kasielke, Corinne book: Urban soils in the Ruhr area. In: Yearbook of the Bochum Botanical Association. Volume 3, 2012, pp. 73-102. ( PDF 6.3 MB)
  2. ↑ Dietmar Brandes: Walls as a habitat for plants. (PDF) TU Braunschweig, accessed on November 5, 2017 .
  3. ↑ Zdena Chocholousková, Petr Pysek: Changes in composition and structure of urban flora over 120 years: a case study of the city of Plzen. In: Flora. 198, 2003, pp. 366-376
  4. ^ Armin Jagel, Peter Gausmann: On the change in the flora of Bochum in the Ruhr area (North Rhine-Westphalia) in the last 120 years. In: Yearbook of the Bochum Botanical Association. Volume 1, 2010, pp. 7–53 ( PDF 9 MB)
  5. ^ Norbert Müller: Lawns in German cities. A phytosociological comparison. In: Herbert Sukopp and others: Urban Ecology. SPB Academic Publishing bv, The Hague, The Netherlands 1990.
  6. ↑ Ken Thompson, John G. Hodgson, Richard M. Smith, Philip H. Warren, Kevin J. Gaston: Urban domestic gardens (III): Composition and diversity of lawn floras. In: Journal of Vegetation Science. 15, 2004, pp. 373-378.
  7. ^ Richard M. Smith, Phillip H. Warren, Ken Thompson, Kevin J. Gaston: Urban domestic gardens (VI): environmental correlates of invertebrate species richness. In: Biodiversity and Conservation. 15, 2006, pp. 2415-2438.
  8. ^ P. Robbins, AM Polderman, T. Birkenholtz: Lawns and toxins: An ecology of the city. Cities. In: The international journal of urban policy and planning. 18 (6), December 2001, pp. 369-380.
  9. ^ CS Lubbe, SJ Siebert, SS Cilliers: Political legacy of South Africa affects the plant diversity patterns of urban domestic gardens along a socio-economic gradient. In: Scientific Research and Essays. Vol. 5 (19), 2010, pp. 2900-2910.
  10. ^ Paul Robbins, Julie Sharp: The lawn-chemical ecology and its discontents. In: Antipode. 2003, pp. 955-979. doi: 10.1111 / j.1467-8330.2003.00366.x
  11. ^ JD Henry: Red Fox. The Catlike Canine. Smithsonian Institution Press, Washington DC 1996.
  12. ^ S. Harris, P. Baker: Urban Foxes. British Natural History Series. Whittet Books 2001.
  13. ^ R. Sullivan: Rats. Observation on the History and Habitat of the City's Most Unwanted Inhabitants. Bloomsbury, New York 2005.
  14. ↑ Per Bolund, Sven Hunhammar: Ecosystem services in urban areas. In: Ecological Economics. 29, 1999, pp. 293-301.
  15. ↑ W. Nylander: Les lichens du Jardin du Luxembourg. In: Bulletin de la Societé Botanique de France, Lettres Botaniques. 13. 1866, pp. 364-372.
  16. ↑ F. Arnold: To Lichen Flora in Munich. In: Reports of the Bavarian Botanical Society. 1. 1891, pp. 1-147.
  17. ^ H. Höppner, H. Preuss: Flora of the Westphalian-Rhenish industrial area including the Rhenish Bay. Dortmund 1926.
  18. ↑ R. Scheuermann, K. Wein: The garden weeds in the city of Nordhausen. In: Hercynia, Abh. Bot. Ver. Central Germany. 1938, pp. 232-264.
  19. ↑ L. Bonte, R. Scheuermann: 1. Contributions to the adventitious flora of the Rhenish-Westphalian industrial area 1913–1927. - 2. Mediterranean plants of the freight yards of the Rhenish-Westphalian industrial area. In: Contributions to regional studies of the Ruhr area. 3, Girardet, Essen 1930, pp. 1–207.
  20. ↑ A. Kratzer: The urban climate. Vieweg, Braunschweig 1937. (2nd, revised and expanded edition. Vieweg, Braunschweig 1956)
  21. ↑ R. Grenzius, H.-P. Blume: Map of the soil associations of Berlin (West) 1: 50,000. In: Berlin Environmental Atlas. 1985.
  22. ↑ R. Grenzius: The floors of Berlin (West): classification, association, ecological properties. Dissertation . Techn. Univ., FB 14 - Landscape Development, Berlin 1987.