A national citizen survey quantified the abundance of epiphytic lichens that are known to be either sensitive or tolerant to nitrogen (N) deposition. Records were collected across the UK from over 10,000 individual trees of 22 deciduous species. Mean abundance of tolerant and sensitive lichens was related to mean N deposition rates and climatic variables at a 5 km scale, and the response of lichens was compared on the three most common trees (Quercus, Fraxinus and Acer) and by assigning all 22 tree species to three bark pH groups.
The major highlights from the study showed that:
- Abundance of N-tolerant lichens was lower on Quercus and other low bark pH species;
- Total N deposition decreased N-sensitive and increased N-tolerant lichen abundance;
- Local busy roads decreased N-sensitive and increased N-tolerant lichen abundance; and
- Reduced N deposition reduced N-sensitive lichen abundance more than oxidised N.
The results from the study demonstrate the unique power of citizen science to detect and quantify the air pollution impacts over a wide geographical range, and specifically to contribute to understanding of lichen responses to different chemical forms of N deposition, local pollution sources and bark chemistry.
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