RBGE Lichens (Home) > Scotland's Lichen diversity

  Scotland's Lichen Diversity  

> 'Biodiversity' is the biological wealth generated over 3.8 billion years of evolution, encompassing genes to species to ecosystems. Human behaviour has dramatically increased rate of species extinction to > 1000 times the 'background level', and we are orchestrating a major global extinction event.

> Typically, 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 itself important in terms of biodiversity - it is celebrated 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 a few of the many reasons why Scotland's lichens are so rich, interesting and important...

> 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 in north-west Europe, where it takes the full force of storms sweeping eastwards across 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).

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

Lichens are found across the world; from the tops of Himalayan mountains, to frigid Antarctica, to the world's hottest deserts. Paradoxically, despite their tolerance of these natural extremes lichens are often incredibly sensitive to human degradation of the environment. This sensitivity allows scientists to use lichens as a proxy-measure 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 of northern Scotland (Figure 3). Lichens indicate the state of the physical environment, which also has important implications for human health. Lichens are a powerful 'bioindicator' for a healthy environment.

> 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 to live and grow from the atmosphere (Figure 4). Experiments have shown that lichens can capture up to 95% of nitrogen deposited in rainfall. Nitrogen is a 'limiting resource' in many ecosystems - there's simply not enough nitrogen to go around.

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.

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

Certain lichens are dispersal-limited (they just don't get around very fast), or they may be restricted to very specific habitats ('niche-limited'): these lichens are associated with ancient forest stands and old-growth structure (Figure 5). Certain of these 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 habitats which provide refugia for rare and specialist lichen species in an otherwise intensively managed and fragmented European landscape.

> Lichens as a source of knowledge...

Science fulfils our 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 ca 30,000 species of lichen). Studying the differences between lichen species (taxonomy), their geographic distributions and systematic relationships provides the opportunity for new and important insights in 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). Symbioses are a fundamental process structuring the natural world. The lichen symbiosis is a testing ground for knowledge about evolutionary and ecological processes structuring symbioses, 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 ideal system to examine the processes structuring biological communities.

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

Figure 1: Epiphytic lichens in woodlands along Scotland's humid 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 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 component of wider research into the biodiversity and ecology of Scotland's natural and cultural heritage.