What were the results?
The results from the survey confirmed findings from other small-scale studies across the country.
The lichen index was significantly lower (meaning there were lots more nitrogen-loving lichens) in areas where nitrogen pollution was increasing.
These included areas in the country with high levels of ammonia from arable farming as well as urban areas where nitrogen oxide levels were high due to increasing road traffic and industry (see the red spots on the maps).
Yellow spots are frequent throughout, especially in areas where conditions are changing and nitrogen-loving species are increasing.
Nitrogen-sensitive lichens were only dominant (blue spots) in areas where both forms of nitrogen pollution were very low.
However the surprising result was that nitrogen-sensitive lichens are now appearing in areas where nitrogen oxide levels were above 12kg/hectare a year (green spots in Figure 1).
This indicates that both nitrogen-sensitive and nitrogen-loving species are present.
Green spots are rare in areas where ammonia concentrations are high suggesting that the nitrogen-sensitive lichens are more affected by ammonia from agriculture whereas the nitrogen-loving lichens respond to increases in both ammonia and nitrous oxides.
The intermediate lichens had varied responses to nitrogen pollution, but their increasing presence in urban areas suggests that but this may be due to other factors such as increasing temperature.
The nitrogen-sensitive lichens decreased in number as average annual temperatures increased.
This was expected as many other researchers have suggested that lichens may be at risk from increasing temperatures caused by climate change.
How well did you identify lichens?
As well as examining the results from the survey, the OPAL scientists wanted to know how well the public can identify lichens.
This is important because it helps scientists assess the reliability of data from the survey.
Thirty-seven students were asked to identify lichens using the OPAL Air Survey field guide on trees that had been previously examined by OPAL Community Scientists. Results varied depending on the type of lichen.
However the nitrogen-loving lichens were correctly identified more than 90% of the time.
The nitrogen-sensitive lichens were correctly identified about 60% of the time. Results from the same survey by OPAL Community Scientists showed that the nitrogen-sensitive Usnea was sometimes confused with Ramalina, a non-indicator species that doesn’t feature in the OPAL guide.
Nitrogen-sensitive Hypogymnia was also occasionally confused with Physcia, a nitrogen-loving species. One of the intermediate lichens, Melanelixia, was often missed.
All of these factors were taken into account when we studied the results of the survey and interpreted the large datasets you collected.
The OPAL scientists concluded that data collected by the public can help scientists find out more about lichens and their relationship to air pollution and climate change.
They also said that the OPAL data has provided a new dataset on urban lichens which can lead to new avenues of research.
Have you submitted your survey results yet?
The more surveys we receive, the more valuable the results become, so we'd love you to take part and submit your findings.
*The OPAL Scientists are the authors of the article.
The full reference for the article is as follows:
Seed, Lindsay; Wolseley, Pat; Gosling, Laura; Davies, Linda; Power, Sally (2013): Modelling relationships between lichen bioindicators, air quality and climate on a national scale: results from the UK OPAL Air Survey. Environmental Pollution, 182:437–47.