A lichen usually is a small organism – the size of its thallus ranges from a few millimetres to a few centimetres. Only some species (e.g. Usnea and Bryoria ) can reach the length of thirty centimetres ( the biggest was Usnea longissima which used to occur in the area of Poland at the end of seventies. Its thallus reached two metres in length). Usnea longissima
Because of their sensitivity to environmental disturbance, many lichens have become endangered species. This sensitivity results from the following factors: lack of a waxy cuticle, which enables a direct infiltration of gases, particulates and solutions into the lichen`s structure ( thallus ); low tolerance of algae to pollutants; absorption of water directly from atmospherical rainfall, without any purification ( plants absorb water partially filtered through the soil).
The role of lichens in the functioning of the ecosystem is often underestimated; after all, they play an important role in nature as pioneer organisms. They grow on the rocks and in the extremely poor environment where only bacteria and algae used to live. They are able to transform inhospitable environment into a habitat for other organisms.
It has been proved that the lichen distribution and diversity correspond with the level of air pollution. On the basis of these findings, the following classes of air pollution have been distinguished: 1 st - lichen utter desert critical air pollution. Even crusty lichens do not occur, at most unicellular algae survive forming green patches on tree barks. 2 nd - lichen relative desert high air pollution Lecanora cnizaeodes and Lepraria are lichen species particularly resistant to pollutants. 3 rd – middle zone of weakened vegetation moderate air pollution In this zone crusty lichens such as Hypogymnia psysodes and Parmelia sulcata can occur.
4 th – outer zone of weakened vegetation relatively low air pollution Evernia prunastri, Pseudovernia furfuracea, Ramalina spp. are foliose lichens but their thalli are deformed and badly developed. 5 th – inner zone of normal vegetation very low air pollution Bryoria fuscescens, Usnea hirta, Plastimatia glauca are fruticose lichens. 6 th – Typical zone of normal vegetation clean air or, at most, slightly contaminated Bryoria, Usnea, Nephroma, Lobaria are fruticose lichens which indicate clean air.
A few years ago, our town used to be a centre of sulphur processing. As a result, the air cleanness was very poor. It was full of sulphur oxides SO 2 and SO 3 and other harmful substances. Our goal was to assess the air condition by lichenoindication method. We decided to search for lichens in Tarnobrzeg. We did our research in the woods, park and cemeteries where we managed to find a number of specimens. Our research group in Tarnobrzeg park. From the left: Kuba Buczek, Kasia Ciak, Danusia Dobrzańska, Marek Makiewicz, Paweł Kowalczyk
Kasia and Paweł are measuring the diameter of lichen thalli.
On young trees in the Tarnobrzeg area we can find powdery lichens (light patches), but the green algae is the most frequent.
In this picture we can see a young lichen ( 1cm in diameter ). So, it has been growing for ten years, as they grow 1mm per year.
On this tree, there are clusters of powdery lichens which indicates a high level of sulphur oxides in the air.
On old trees we can find large clusters of foliose lichens which proves that the air condition in Tarnobrzeg has improved.
This photo shows Hypogymnia physodes and Xanthoria parietina.
This is a large specimen of Hypogymnia physodes.
On the walls we can observe large clusters of Xanhoria parietina.
This is a group of Xanthoria parietina which has not covered the whole surface yet.
Although a few years ago our town and its surroundings used to be a lichen desert due to a high level of harmful gases in the atmosphere, today we can find several specimens of lichens which are bioindicators of air cleanness. They range from 2nd to 4th classes. Thus, we can draw the conlusion that that the air condition has greatly improved. Unfortunately, fruticose lichens belonging to 5th and 6th classes do not occur.