Evol Ecol Res 6: 749-764 (2004)     Full PDF if your library subscribes.

The flora of German cities is naturally species rich

Ingolf Kühn,1* Roland Brandl2 and Stefan Klotz1

1Department of Community Ecology, Centre for Environmental Research Leipzig-Halle, Theodor-Lieser-Str. 4, 06120 Halle and  2Department of Animal Ecology, University of Marburg, Karl-von-Frisch-Straße, 35032 Marburg, Germany

Author to whom all correspondence should be addressed.
e-mail: ingolf.kuehn@ufz.de


Previous studies on various scales and for various European regions and North America have shown that cities harbour more plant species than the surrounding landscape. It has been argued that the greater number of plant species is usually caused by a high number of alien plants promoted by human influence. We analysed native and naturalized vascular plant species distribution data from a comprehensive German database comparing city and non-city grid cells of 10 minutes latitude × 6 minutes longitude (c. 130 km2). The number of city grid cells (n = 68) and non-city grid cells (n = 1856) differed by two orders of magnitude and species richness was highly autocorrelated. We therefore used resampling techniques. We resampled the species richness of 68 randomly selected grid cells 9999 times. This showed that not only naturalized alien but also native plant species richness was significantly higher in city grid cells. To relate environmental variables to species richness, we used 10,000 analyses of covariance of 68 city grid cells and 68 randomly selected non-city grid cells. We demonstrated that a large proportion of the higher native plant species richness could be explained by the number of geological types per grid cell (i.e. a measure of natural geological diversity). Additionally, we showed by resampling the number of geological types per grid cell that cities are not randomly distributed but are in fact in areas of high geological diversity. Hence, we conclude that city areas are preferentially located in pre-existing biodiversity hotspots and argue that they are species rich not because of but in spite of urbanization.

Keywords: alien plants, environmental correlates, environmental heterogeneity, native plants, resampling methods, species richness, urbanization.

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