scope:

Introduction

Lichens are extremely sensitive to environmental stress, especially that caused by atmospheric pollution, eutrophication and climate change [10; 12; 16; 18; 30; 35]. The main reasons are:

delicate symbiotic association between the lichen partners fungus and alga

Unlike higher plants, lichens have no cuticle (protective layer); pollutants can therefore readily penetrate to the fungal and algal cells.

Substances are taken up direktly from the atmosphere.

Lichens continue to metabolize at low temperatures and are therefore susceptible to damage during the winter months. Lichens grow slowly and regeneration after injuries is also slow. Lichen diversity is an excellent indicator of stress by atmospheric pollutants both of the acidifying and the eutrophicating kinds [5; 9; 11; 14; 17; 18; 27; 29; 31; 32]. Lichens respond relatively fast to quantitative and qualitative changes in air quality. They can re-colonize urban and industrial environments within a few years after the conditions have improved. This has been observed in many regions of Europe [7; 11; 13; 19; 20; 21].

This VDI guideline proposes a standardized method to assess lichen diversity on tree bark. Results are shown in maps indicating zones of different diversity from which it is possible to determine air quality gradients. The method is also suitable for observing the temporal changes in the lichen flora, and thereby increases or decreases in air quality.

This method of mapping lichens is adapted to Central European conditions. It is based on a proposal for a uniform method for all of Europe [3].

A guideline based on the same proposal exists in Italy [1].