Scotland's Lichen Diversity  

Epiphyte Ecology
Monitoring Change
Species Discovery

Dr Brian Coppins
Ms Sally Eaton
Dr Christopher Ellis
Ms Louise Olley
Dr Rebecca Yahr

Research Projects




'Biodiversity' is the biological wealth generated over 3.8 billion years of evolution, encompassing genes to species to ecosystems. Biodiversity is now threatened: human activities have increased rates of species extinction to > 1000 times the 'background level', and we are orchestrating a major global extinction event.

When people choose to celebrate or protect 'biodiversity', they might think of Australia's Great Barrier Reef, the Brazilian Rainforest or the great plains of Africa. Few people realise that Scotland is internationally important in terms of biodiversity, particularly for the richness of its cryptogamic plants and fungi.

Cryptogamic plants and fungi account for over 84% of global 'botanical' diversity. They include the ferns and horsetails, algae, mosses, liverworts and fungi including lichens. Scotland is a European 'hot-spot' of lichen diversity. Scientists at RBGE carry out research to understand and protect Scotland's lichens, and this page explores five reasons why Scotland's lichens are so diverse and important...

1. From rainforest to arctic tundra, Scotland has it all...

The Scottish climate is unique in Europe. This is partly because of Britain's island position, where it takes the full force of storms sweeping eastwards off the Atlantic.

However, the Scottish mountains generate a rain-shadow effect, creating a steep climatic gradient across Scotland; from the wetter though milder west coast to the drier east, with cooler winters.

Lichens respond dramatically to this variation in climate and topography. Studying Scotland's lichens can take you from temperate rainforest to arctic tundra in a single weekend (Figure 1 & Figure 2).

2. What's good for lichens, is good for us...

Lichens are found across the world; from the tops of Himalayan mountains to the inter-tidal zone, and from frigid Antarctica to the world's hottest deserts. Paradoxically, despite their tolerance of these natural extremes, lichens are often incredibly sensitive to human damage to the environment.

This sensitivity allows scientists to use lichens as a bioindicator for pollution, e.g. acid rain (SO2 pollution), and hypertrophication (excessive nitrogen and phosphorus). Contrast the bare twig from a city-centre park with a twig from the clean air environment in northern Scotland (Figure 3).

By indicating the quality of the physical environment, lichens have important implications for human well-being. See our guide to Lichens as Urban Air Pollution Indicators.

3. Food from fresh air...

Lichens don't need soil - they can grow on bare rock and on branches at the tops of trees. They capture the nutrients they need from the atmosphere (Figure 4).

Experiments have shown that lichens can capture up to 95% of nitrogen deposited in rainfall. Nitrogen is a 'limiting factor' in many ecosystems; there's simply not enough nitrogen to go round. As well as capturing nitrogen from rainfall, some lichens can 'fix' nitrogen gas (N2) directly from the atmosphere.

Because of their effectiveness at capturing scarce nutrients, lichens are extremely important in primary succession (the early stages in ecosystem development) and in the nutrient balance of oligotrophic (nutrient-poor) ecosystems.

4. Telling the story of Scotland's ancient forests...

Certain lichens are dispersal-limited and move between habitat slowly, or they may be restricted to very specific habitats ('niche-limited'): these lichens are associated with old-growth structure in ancient woodland stands (Figure 5).

Such lichens are indicators used to infer habitat continuity, i.e. how long a woodland has existed at a site; the assemblage of lichens therefore tells a story about woodland history. Scotland has ancient woodland that provides refugia for rare and specialist lichen species in an otherwise intensively managed and fragmented European landscape.

5. Lichens as a source of knowledge...

Science fulfils a need to better understand the natural world, and the role of humanity within it. The science of lichens (lichenology) provides important new insights not just about the lichens themselves, but about natural history more generally (Figure 6).

Lichens evolved at least 400 million years ago, they occur on every continent and are extremely diverse (there are thought to be c. 30,000 species of lichen). Studying the differences between lichen species (taxonomy) provides the opportunity for new and important insights into the diversity and evolution of life.

Lichens are the classic example of a symbiosis, i.e. between a fungus (which builds the lichen body, the thallus) and a photosynthetic partner (which provides a source of carbon). Symbiosis is a fundamental property of the natural world. The lichen symbiosis is a testing ground for knowledge about evolutionary and ecological processes, and the nature of close species interactions.

Lichens include a vast array of growth forms, physiologies and strategies for reproduction and dispersal ('ecological traits'). Their communties are structured at contrasting scales, from kilometres to millimetres, and these contrasts provide ecologists with an excellent system to test the dynamics of ecological communities.

Perhaps most importantly, lichens are a beautiful part of the natural world around us; they inspire great wonder and can be enjoyed by absolutely anyone with a sense of curiosity.

Figure 1. Epiphytic lichens in woodlands along Scotland's oceanic west coast include 'temperate rainforest' communities. To experience a similar lichen habitat you might travel to western North America or New Zealand. Scotland's woodlands provide an internationally important and globally rare example of lichen-rich temperate rainforest in Europe. The picture shows Lobaria pulmonaria, now rare and threatened over much of Europe, the species has a stronghold in western Scotland.
Figure 2. The summits of the Cairngorm mountains in north-east Scotland have low temperatures and high wind speeds. The growth of plants is extremely limited by the harsh environment, but lichens can tolerate these extreme conditions, thriving in the absence of competition from taller species. The lichen-rich plateau provide out-lying examples of lichen communities normally associated with Scandinavian tundra.
Figure 4. The lichens growing on this branch are not parasitizing the tree - lichen epiphytes don't harm the trees on which they grow, they sequester the nutrients they need from the atmosphere.
Figure 5. Ancient woodlands provide refugia for some of Britain's rarest lichens. Scotland includes important examples of semi-natural and near old-growth habitat, as here in the Caledonian pinewood, Glen Affric.
Figure 6. Studying lichens is an important part of research into the biodiversity and ecology of Scotland's natural and cultural heritage.