During the winter, when the leaves fall off trees, these small sometimes unseen beauties can be better appreciated, though they can be seen all the year round.
Although they can grow on almost any surface; rock, metal, glass, plastic, walls, bone, leather, paint, fences, pavements, soil, rocks, grave stones, old houses – it is on the trees in the internationally important Atlantic / upland western oak woodland that they are most renowned.
Dartmoor is one of the best places to see these enchanted parts of the ecosystem, and they form the basis of many ecosystems. Lichens, in part make Dartmoor an Important Plant Area (IPA), thanks to the clean air from the Atlantic and the stable habitats. One of these habitats is the special upland western oak woodlands. Here oak trees can outlive eight generations of us, so these woods provide the stable habitats that lichens need, if the surrounding oak woodland does not shade them out.
At East Dartmoor National Nature Reserve, these woodlands are better known as the Bovey Valley Woods and Yarner Wood. These woods are so special for the lichens assemblage, they come under the Site of Special Scientific Interest (SSSI), like other SSSI on Dartmoor.
Here Natural England and the Woodland Trust are working with Plantlife, on a Heritage Lottery funded Building Resilience in South West Woodlands project to give more light to the valuable old wood bank trees. These wood banks have been selected to link up known areas, where lichens are both numerous and special. The aim is to include interested people where necessary to monitor these wood banks, before and after necessary thinning of shade casting trees. We are currently in the development year of the project, it would be useful if anyone is interested in monitoring the wood banks, or any other part of the project, follow this link to the project page. You can also take part in a Plantlife survey about woodlands – please follow this link to take part.
Lichens need light because they are a symbiotic relationship between an algae, or cyanobacteria (blue-green alga), and fungus. Imagine a microscopic slice of iced fruit cake. What we see could be seen as the icing only. The fungus is represented by the body of the cake while the algae is sort of like the pieces of fruit. The alga cyanobacteria enables the lichen to function in humid conditions and low light; these lichens are particularly good at trapping atmospheric nitrogen and carbon makes energy via sunlight for this species. The fungus ensures the alga exists in the best conditions for it to function to the mutual benefit of both partners, protecting it from drying out, drowning, freezing and UV protection. As both of these are microscopic the energy they can gain from the sun (by the algae) and the nutrients through the rain (by the fungus) means they hardly change from one year to the next.
Once you start taking a closer look at these wonderful, colourful organisms you see a beauty we often walk past. Lichens come in all shapes and sizes sometimes covering the surface we see. Here are the most common forms; powdery, crusty, leafy, shrubby, Pixie cup, scaly, pin-head, jelly, bracket. When first starting to look at lichens on nature reserves it is easiest to categorise them into 3 simple groups…
CRUSTY – crustose; Crust-like lichens that are only removed by cutting the bark.
LEAFY – foliose; Leaf-like lichens attached by the lower surface.
SHRUBBY – fruticose; Branched shrub-like lichens attached by a sucker-like holdfast. A good example of these are the Usnea’s
Some of the charismatic priority species lichens, such as Usnea florida / witches whiskers and Usnea articularta / string of sausages, are sadly declining. Natural England are studying these lichens with volunteers and Natural Science students from the University of Exeter, to help record changes over time.
Lichens grow VERY slowly – from as little as 100ths of millimetres to 2-3mm a year. They can survive many hundreds of years and their growth can be measured to determine the movements of glaciers or the frequency of volcanic eruptions over time. By looking at the date on a grave stone and measuring the size of the largest lichen growing on it, you can work out the age of the lichen and how slowly or quickly it grows.
Pollution is a serious threat to lichens especially in urban and industrial areas. Lichens are sensitive to precise levels of pollution (from sulphur dioxide) and they can be used as biological indicators of air quality. Lichens act like sponges, taking up pollutants. Lichens are still used in medicines, dyeing, and have been used by archaeologists to date artefacts and track geological events since the retreat of the glaciers.
So over this winter take a closer look at lichens around you and be amazed by the beautiful microscopic world.
Written by Albert Knott, Natural England Reserve Manager, for the Dartmoor National Nature Reserves
Natural England and the Woodland Trust are both partners in the Plantlife project ‘Building Resilience in South West Woodlands’. To find out more and see how you can get involved at Building Resilience in South West Woodlands
Plantlife are interested in finding out how local people use woodlands and how they would like to get involved – please take part in their online survey here – Plantlife Survey