What is air pollution?

Air pollution is often associated with the deposit of black particles seen on windows, leaves and buildings in urban areas. However, much of the air pollution in Britain today is largely invisible and so more difficult to detect, although you may be able to smell the pollutents from car exhausts, farmyards and heavy industry.  Some pollutents contain ammonia and oxides of nitrogen (nitric oxide and nitrogen dioxide). Although nitrogen is essential for the growth of all living organisms, too much nitrogen can cause problems. Ammonia and oxides of nitrogen can stimulate the growth of some plants and fungi but stop others from developing, thereby changing the natural around us. Lichens do not like excessive nitrogen in any form, but may grow particularly well when they are growing close to sources of ammonia. There is also a fungus, commonly known as tar spot that is found on sycamore trees, that we believe is sensitive to air pollution including nitrogen dioxide.

Where to find lichens?

Lichens will grow on almost any surface including trees, rocks, earth and artificial surfaces such as concrete and tarmac. Lichens grow best in light  where they are not competing directly with tall grass, shrubs and climbing plants. Lichens that are highly sensitive to air quality and have been used to detect sources of pollution. In the past, when the air in many places was highly polluted by sulphur dioxide, few lichens could survive, creating lichen deserts around many industrial and urban areas. Lichens are now returning to British towns and cities, and they can still provide a great deal of information about our air quality.

What do lichens look like?

Unlike mosses and flowering plants, lichens do not have green leaves or a stem. They may be pale or bright coloured and commonly occur in three forms.

1, Leafy lichens have leaf-like lobes closely or loosely attached to the bark from the lower surface.

2, Bushy lichens are branched and shrub-like, attached to the bark at the base.

3, Crusty lichens are closely attached as if painted on the bark.

What are lichens?

In my next set of blogs i am going to be talking about lichens and the air quality that surrounds them.

Lichens are made up of two or more different organisms living together, a fungus and an alga. The fungus provides the body (thallus) in which the algal partner can live, protected from damaging conditions such as high levels of light (ultraviolet radiation) and lack of water (drought). The algal partner provides the essential carbohydrates (food for the fungus) from carbon dioxide and water, with the aid of sunlight. This close, interdependent relationship is referred to as a symbiosis.