Levels of human impact on ecosystems

Before considering the needs for conservation and how ecosystems can be utilised to our long-term advantage, it is necessary to evaluate the impact that people have on ecosystems.

The level of impact on ecosystems should be viewed in relation to the landscape or habitat type that is being affected. A hierarchy of landscape and vegetation types against which impacts could be judged, described in 1971 by V. Westhoff in ‘Dynamic structures of plant communities’ (In Duffey, E. & Watts, A. S. (eds.) Scientific management of plant and animal communities for conservation, Blackwell Scientific), takes into account the degree of intervention in ecosystem processes and the consequences of that intervention on the structure (formation and physiognomy) of the plant communities. They are:

1. 1 Natural landscape

2. The flora and fauna are uninfluenced by people. (Westhoff suggests that this type no longer occurs in western and central Europe.)

3. 2 Subnatural landscape

4. The flora and fauna are similar to the potential natural vegetation in species composition and structure (and hence appearance), but the influence of people can be measured.

5. 3 Semi-natural landscape

6. The plant communities are to a large extent indigenous but the vegetation type has been essentially changed by human activity. The plant communities present a different structure and appearance to the expected natural vegetation. Examples of this in the UK are unimproved grasslands, heathlands and moorlands, which would all be expected to develop into woodland if not managed in some way.

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