The Ecosystem Overviews provide a summary introduction to the main habitat types covered in APIS and the main air pollutant pressures to those habitats in the UK. In specific locations, e.g.close to a major source, other pollutants may be a concern for a habitat and the user should use the searches by location or by habitat/pollutant in these cases.
Inland rocky habitats of particular conservation value include natural rocks and cliffs, scree and limestone pavements. Each of these habitats is characterised by grasses, dwarf-shrubs and/or herbs growing in restricted crevices. In many cases the result of this is that competition for light is less of an issue than in closed grassland canopies, so that the interaction with air pollutants may also differ. Currently, there is a lack of data on these interactions, and expected effects must be derived from experience with other habitat types.
BAP habitats: Limestone pavements (priority); Maritime cliff and slopes (priority); Inland rock outcrop and scree habitats (priority).
Main Pollutant Impacts
As with grassland habitats, nitrogen deposition will affect the competitive performance of species growing in rocky habitats. Lower critical loads for nitrogen are generally set for acid habitats, than for calcareous habitats, some of which may be P limited rather than N limited.
Nitrogen deposition impacts may also occur directly to lichens and bryophytes growing on rocks. In this case, however, effects may equally be a response to elevated concentrations of NOx and NH3, which would occur mainly in lowland areas.
Although calcareous rocks tend to be weathered faster by acid deposition (for example, as causing damage to stonework of buildings), this very weathering provides a buffering to protect species growing in such habitats. Acid deposition is therefore more likely to be an issue in already naturally acidic rocky habitats, with little neutralisation capacity.
As with other semi-natural habitats, ozone effects may be expected for rocky habitats, given the exceedance of the critical level over much of the UK. However, there is an extremely limited data set available. The only available study on limestone pavement observed no adverse effects from ozone fumigation to plant species grown from seed collected from limestone pavement SSSIs in the Yorkshire Dales National Park (Ashmore and Keelan, 2006).