Clinging onto trees, rocks, gateposts and buildings there’s a wide range of miniature ecosystems that are so common, we often overlook them. They are another example of one of nature’s incredible relationships – the lichens.Abundant lichens cover up to 7% of the earth’s surface and can be found across hostile environments from the Arctic to the deserts and the coastlines, but despite this success human factors including their sensitivity to air pollution and the loss of ancient woodlands has already impacted on them. Present all year round, their colours and intricate textures really stand out during the winter months.

Success through duality

Described by the Greek botanist, Theophrastus as emerging from tree bark, lichens were once believed to be forms of seaweed or moss. First recognised as part of the fungi kingdom in the late 19th century, lichens are compound organisms, formed through a symbiotic relationship between a fungus and an alga, or cyanobacteria (blue-green alga). The fungus (the mycobiont) forms 90 - 95% of the body or thallus of the lichen and gives the alga a safe environment protected from temperature changes, as well as access to water and nutrients. In return the alga (the photobiont) photosynthesises and gives the fungus the sugars it needs to grow and reproduce. It’s a long-standing relationship which fossil records show dates back at least 250 million years. Recent research, however, has started to question whether this is an equal partnership, or whether the alga is being ‘farmed’ for its sugars.[gallery type="slideshow" size="large" ids="9409,9408,9407"]

Crusty pioneers and nitrate suppliers

Recognised as pioneer species, crustose lichens are the first organisms to colonise rocks, from lava flows to newly exposed rocks in sidings and quarries. Making up 75% of all lichens they form thin crust like surfaces and are fully attached to the rock through a series of root like rhizines that are part of their thallus. They gradually penetrate the rock releasing organic acids, whilst also expanding and contracting depending on whether they are wet or dry, which slowly erodes the rock’s surface, releasing minerals, and starting the gradual process of soil formation.About 10% of lichens have a cyanobacteria partner which enables them to convert nitrogen from the air into nitrates. Over time the nitrates are released into the soil, either by being leached out when it rains, or when parts of the lichen fall to the ground and decompose. So indirectly, the cyanobacteria-based lichen’s presence improves the soil’s fertility and makes the nitrates available to plants.[gallery type="slideshow" size="large" ids="9416,9406,9414,9405"]

Value to wildlife

Lichens are such an integral part of their ecosystems that a wide range of insects, invertebrates, birds, and small mammals have come to rely on them. Moths have developed distinctive wing patterns to help them blend into the lichen that grow on trees to avoid predators, while snails, squirrels and voles use them to supplement their diets. The textured surfaces of leafy (foliose) and shrubby (fruticose) lichens provide shelter and food for a wide range of invertebrates such as spiders and mites, while birds such as the long-tailed tit, chaffinch, and hawfinch, use small pieces of lichen to camouflage their nests.

Looking out for lichen

Of the 1,900 species in the UK, 900 can be found in Devon, and over the centuries we’ve used them for their inflammatory and antibacterial properties to treat wounds and respiratory problems such as whooping coughs, and as a fixative in perfumes. Our longest use however has been making dyes and until synthetic dyes were introduced tonnes of lichen were collected by local people to supplement their incomes and taken to collection points such as Okehampton before being shipped to factories as far away as northern England.Now the clean air, steady rainfall and climate across Dartmoor and its wooded valleys is providing them with a haven and are one of the reasons why Dartmoor is an Important Plant Area (IPA). Locally Yarner Wood and Bovey Valley Woods (East Dartmoor National Nature Reserve) has become a Site of Special Scientific Interest (SSSI) and patient monitoring is showing that lichens prefer a diverse woodland area with open and closed canopies, patchy understoreys, and a mixture of standing and fallen wood. Veteran trees and varied landscapes that include riverbeds and rocky outcrops are also factors in lichens’ success and all of them are particularly important for fruticose lichens, especially beard-like or strap-shaped, which are the most vulnerable group of lichens to air pollution.[gallery type="slideshow" size="large" ids="9411,9412,9410,9413"] It’s heart-warming to know that all the effort volunteers have made to clear conifers, let in the light, and create open spaces, as well as the practice of leaving dead wood is supporting lichens. In 2017, Neil Sanderson, a visiting lichen expert, discovered Varicellaria Velata in Fingle, which was last recorded on Dartmoor in the late 19th century. If we all look out for lichen, who knows what else we might find. Written by Jane HallidayPhotos by Jane Halliday and Stella Horton