Impact Type: Direct exposure to pollutant
Most Ramalina spp. are very sensitive to SO2 which has resulted in their disappearance from much of their former range.
R. farinacea which can stand up to 60 µg m-3, but it has disappeared from some parts of its former range in north-central England, London and Central Scotland due to air pollution (Seaward & Hitch 1982).
R. fastigiata which can stand mean winter levels of SO2 up to 35 µg m-3, has disappeared from centeral and northern England (Seaward & Hitch 1982).
R. fraxinea which can also stand mean winter levels of SO2 up to 35 µg m-3, is now very rare or extinct in most of central and SE England where it was once common (Seaward & Hitch 1982).
The critical level for Ramalina spp. may need to revised downwards (Bates 2001).
|Habitat/ Ecosystem Type||Critical Load/ Level||Status||Reliability||Indication of exceedance||Reference|
|Forests and semi-natural vegetation||
20 µg SO2 m-3 annual mean and half-year(Oct-March) mean
|UNECE, 2004||quite reliable i.e. the results of some studies are comparable||
Low temperature appears to enhance the negative effects of SO2, and the lower critical level of 15 µg SO2 m-3 is used where the effective temperature sum (ETS) (i.e. the sum of temperatures) above 5oC is below 1000 degree days (d.d) (Ashmore et al., 1994).