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Lichen Pollution Meters

Lichens could be used as bio-indicators of air pollution, according to Landcare Research scientists who are studying lichens in Christchurch and Taranaki to see which are the best pollution indicators.

The team has found that the number of lichens increases away from urban and industrial areas. Dr Peter Johnson says that some of New Zealand's 1,200 lichens are better than others at indicating pollution levels.

"In the face of air pollutants, some lichens act as fall-guys while others don't seem to mind a bit of filth," he says. "As you move from the centre of Christchurch from the zone where sulphur dioxide levels are highest in winter smogs, out to the cleaner countryside, you follow a gradient of increasing lichen cover and diversity."

Colin Meurk notes that certain species of lichen are particularly sensitive to sulphur dioxide. Only one or two sulphur-tolerant species may be found in polluted areas, with the numbers increasing as the sulphur dioxide levels drop. The physiological reasons behind the sensitivity are not well understood, but they provide a means of mapping pollution which would be cheaper than conventional sampling and monitoring.

The team has been gathering data on lichen species and distribution and comparing these with already held information on pollution levels. They are hopeful that the analysis will reveal a reliable correlation between the two which would enable extrapolation of their results to other areas. The study has had to be selective in the trees used as lichen sources.

"We ignored trunks having major bark damage, too many air rifle pellets or the dazzle paint messages that are the modern equivalent of carved initials. The lowermost half-metres of trunks was also excluded, being either the herbicide impact zone or the dog piddle zone."