More plant species grow in German towns and cities than in the countryside, but those in towns and cities are more closely related and are often functionally similar. This makes urban ecosystems more susceptible to environmental impacts.
This is the finding of ecologists at the Helmholtz Centre for Environmental Research (UFZ) who evaluated 14 million entries in the German national FLORKART database, which has been built up by several thousand volunteers over the past few years. They claim that because of the altered environmental conditions, nature conservation needs to look not only at conserving as many species as possible, but also at other aspects of species diversity.
Writing in the October issue of Ecology Letters, the researchers say that since urbanisation is already far advanced and will continue to advance in future, we need to develop strategies to protect species diversity even within towns and cities.
The urbanisation of the world is increasing rapidly. More than half of the world’s population lives in towns and cities. In Europe the figure is as high as 70 per cent. The fact that there is a higher number of species in towns and cities than in the surrounding countryside is due to a number of different reasons: many towns and cities developed in geologically and structurally diverse landscapes, so are naturally rich in species; the towns and cities themselves have very diverse structures, temperatures are higher than in the surrounding countryside, and alien species are often introduced into towns and cities.
However, although towns and cities harbour more species than the surrounding countryside, in terms of conserving biological diversity it is not just the number of species that matters, but also their relatedness (i.e. phylogenetic diversity). Every species is a carrier of inherited information that determines e.g. pollination method and leaf structure. The greater the phylogenetic diversity of a community, the greater the probability that it will contain species with different traits.
The traits and, consequently, the phylogenetic diversity, are therefore the tools that enable plant communities to respond to different environmental events. Without knowledge about traits and relatedness (phylogenetics) our understanding of how communities develop and how they deal with altered environmental conditions will remain incomplete.
For their study, the researchers laid a grid of cells, each around 12 kilometres wide, over Germany and characterised the cells in terms of land use. 59 cells were classified as urban landscape, 1365 as agricultural and 312 as forest or near-natural landscapes. “Our findings lead us to believe that different environmental filters operate in urban areas and in rural areas,” explains Sonja Knapp of the UFZ. The loss of phylogenetic information reduces a community’s ability to respond to environmental changes and could in the long term have a negative impact on the functions of urban ecosystems.
- Knapp et al. Challenging urban species diversity: contrasting phylogenetic patterns across plant functional groups in Germany. Ecology Letters, 2008; 11 (10): 1054 DOI: 10.1111/j.1461-0248.2008.01217.x
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