Impact Type: Direct exposure to pollutant
Work by Caporn et al. (2000) has shown that exposure of Calluna to elevated SO2 and NO2 throughout the growing season, may lead to an increase in both root and shoot growth. However they found that this was offset by an increased risk of damage by frost and an imbalance in root/shoot growth, which make the plants more vulnerable to water stress. No work appears to have been published as to the separate effects of these two pollutant gases on Calluna.
With declining SO2 concentrations in the UK, Calluna is not generally thought to be under threat from this pollutant.
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|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).