Study
Qualitative scale for estimating sulphur dioxide air pollution in England and Wales using epiphytic lichens
Hawksworth, David L.; Rose, Francis
Nature, 1970
Epiphytic lichen communities were surveyed across England and Wales against measured sulphur dioxide concentrations, and the species present at each level were assembled into a ten-point scale that allowed air quality to be read from the lichens on a tree.
- Studied in
- Lecanoromycetes
- Sample size
- lichen communities surveyed across a pollution gradient
Lichen species drop out in a consistent order as sulphur dioxide rises. Sensitive shrubby and leafy species disappear first, crustose species persist longer, and above a threshold bark carries only algae. The sequence was regular enough to estimate pollution from the flora alone.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Epiphytic lichen communities can be used as a quantitative biological indicator of sulphur dioxide pollution.
How NatureHQ reads it
A living instrument, and a rare case where the biology is genuinely more useful than a meter for some purposes: lichens integrate exposure over years, so they report what the air has been like rather than what it is like this afternoon. The scale is specific to sulphur dioxide and to a particular flora — it is not a general pollution meter — and its own success dated it, because British air improved enough after clean air legislation that sensitive species have been returning to cities for decades.
- Calibrated for sulphur dioxide specifically; nitrogen compounds affect lichens differently and now dominate.
- Regional to England and Wales; the species sequence differs elsewhere.
- Substrate, bark chemistry and local climate all shift the community independently of air quality.
Reading sulphur dioxide off the bark of a tree
Air quality monitoring in 1970 meant instruments, and there were few of them. Could the organisms already growing on every tree be read as a record of the air instead?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Nature PortfolioPublished in a Nature Portfolio journal.
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-10.