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The following is an excerpt from Urban Protected Areas (page 4).

In the context of urban protected areas, it may be useful to think of degrees of naturalness, from the most natural to the least:

10  Natural virgin system (only natural elements and processes are present)

9  Natural system (few exotic species are present)

8  Sub-natural system (there is possibly an extended presence of wild exotic species, but with low impact)

7  Quasi-natural system (extensive human activities, but with low physical impact)

6  Semi-natural system (human infrastructure is scarce or concentrated; wild exotic species are possibly dominant, with native species considerably reduced)

5  Cultural self-maintained system (processes are conditioned by extensive human activities, with native species altered and occasionally managed)

4  Cultural assisted system (there are important infrastructures and/or conditioning of the physical environment, with forced biological production and moderate addition of matter, usually with pollution added)

3  Highly intervened system (still includes areas with natural, cultivated, or breeding biological production, mixed in a mosaic with buildings and other infrastructure)

2  Semi-transformed system (biological production is not dominant; human elements predominate)
1  Transformed system (human processes govern, with clear dominance of artificial elements)
0  Artificial system (there is no self-maintained macroscopic life; microscopic life is absent or in containers) (adapted from Machado, 2004)

When presenting this index at conferences, its author, the Spanish biologist and conservationist Antonio Machado, sometimes uses an orchestral metaphor: above 5, nature holds the baton; below 5, man holds it.

The urban protected areas described or mentioned in this book generally fall between 8 and 6 on this scale. Parts of them may fall in 9 or 5.

By contrast, most urban parks are likely to fall into point 3 on the scale. While they may contain quite varied plant and animal life, this is often made up mainly of plant species that are not native to the area, as well as non-native animals. For example, New York City’s Central Park is sometimes cited for its high biodiversity as it has some 479 species (Explorers Club 2008), but most of these are not native to the region or even to North America. Nevertheless, non-native species can play a significant role in giving urban people some experience of nature.

Explorers Club. 2008. ‘Central Park Bioblitz 2006, Survey Results.’ New York: The Explorers Club.

Machado, Antonio. 2004. ‘An index of naturalness.’ Journal for Nature Conservation 12: 95-110.


Riiser-Larsen Ice Shelf, Antarctica: Probably a 9 (Natural system)

Index of Naturalness

Central Park, New York City: Probably a 3 (Highly intervened system). Sometimes citied for its high biodiversity, Central Park   has some 479 species of plants and animals, but most of these are not native to the region of even to North America