Changes in the lichen vegetation at the long time investigation areas Melsungen and Limburg (Hesse/Germany) between 1997 and 1999

A new procedure was used for the assessment of trends of the air pollution situation at six hessian permanent lichen monitoring plots in 1997: At 1200 freestanding deciduous trees a quantitative recording of the coverage of t he existing lichen thalli was carried out on an area of 20 x 20 cm. A trans parent foil (400 cm(2)) was fastened on the trees, The contours of the thal li were transferred to the foils with felt-tipped pens. After digitalizing the: foils an area calculation of the lichens occur-led by a special softwa re, developed for this purpose. The marked squares of two permanent monitor ing plots (Melsungen, Limburg) were examined after two years again (1999). The changes in coverage could be evaluated statistically and graphically. The results show a distinct drive in the lichen coverage: On the one hand t he acidophytic and toxitolerant Lecanora conizaeoides is vanishing almost c ompletely. On the oilier hand an increase of nitrophytic species such as Ph yscia tenella, Phaeophyscia orbicularis, Xanthoria candelaria, X. parietina and X. polycarpa on the standardized investigation areas is obvious. It is intended to establish the presented method as a new VDI-guideline in suppl ementation to the existing lichen mapping guideline.