Bryophyte and lichen indicators of air pollution in Christchurch, New Zealand
- Department of Plant Science, Lincoln College, Christchurch
In the winters of 1968 and 1969 a survey was made of the growth and distribution of bryophyte and lichen species within communities on tree trunks, stone walls, non-metallic roofs and soil in Christchurch, New Zealand. The survey was stimulated by European and Scandinavian work which has shown that high levels of urban and industrial air pollution have caused severe reductions in the distribution of normally-abundant cryptogams. The present survey has demonstrated that a similar, but at present less severe, reduction in bryophyte and lichen flora occurs in Christchurch. Removal of sensitive species through their inability to grow lilt even moderate levels of winter pollution is considered the most likely cause.
An initial transplant experiment indicates that damage to sensitive mosses like Hypnum and Brachythecium may occur within 3 months of exposure to city air. Gilbert and others have shown that, in northern England, sensitive mosses and lichens begin to die when the average winter sulphur dioxide level reaches 50 μg./m3 of air. This relationship has been confirmed in Christchurch, a moderately polluted city.
Numbers of species and the area covered by sensitive mosses, hepatics and lichens reduce sharply along a broad transect into the centre of Christchurch from the west. Further work should display the distribution patterns of sensitive species. However, the information reported here demonstrates the possibility of using changes in selected mosses and lichens to indicate the trends in winter sulphur dioxide pollution in the city.
Many of the genera and species of bryophytes and lichens prominent in the English survey were also found to be common in Christchurch. Introduction on plants and building materials during colonial times is considered likely.