The Lichens and Lichenicolous Fungi of Belgium and Luxembourg ...

THE LICHENS OF BELGIUM AND LUXEMBOURG. AN ANNOTATED CHECKLIST 15
Fig. 6. The death of elms has very seriously damaged the epiphytic lichen flora, especially in
the western parts of the study area. Photograph: E. Sérusiaux (1982).
La disparition des ormes a très sérieusement endommagé la flore des lichens épiphytes, en
particulier dans l’ouest du territoire étudié. Photographie: E. Sérusiaux (1982).
De sterfte van iepen heeft de epifytenflora veel schade toegebracht, vooral in het westelijk deel
van het onderzoeksgebied. Foto: E. Sérusiaux (1982).
The Brabant district (here after Brab.) is a large, gently undulating plateau, rarely over
200 m elevation, which is mostly covered by loess deposits from the Pleistocene. Except for
several forested sites that usually correspond to sandy and less fertile emergences, the area
is mostly used for intensive agriculture. The lichen flora is thus very reduced, and much so
that the Haine-Sambre-Meuse depression that borders the district on its southern parts is
very industrialized and polluted. The strong atlantic traits that are so characteristic of the
forest ground flora, especially in the western part, are no longer expressed in the lichen
flora, which is now reduced to ubiquitous and toxitolerant species. Several small rock
outcrops exist in the valleys but their lichen flora is very poor.
The Meuse district (here after Mosan) has an altitude fluctuating between 200 and 300
m and enjoys a better air quality than the previous districts. It shelters an exceptional
lichen flora owing to the numerous natural rock outcrops that are to be found in the main
valleys, especially along the Meuse, Viroin, Lesse and Ourthe (Fig. 7). Those calcareous
rocks are usually very compact and date back to the Devonian or Carboniferous. The
lichen flora associated with the Xerobromion communities show strong submediterranean
affinities, and many species are at the northern limit of their distribution area. Other
outcrops, covering a smaller surface, are markedly siliceous and also of high interest. The
lichen forest flora is rather trivial, with a few exceptions linked to the best preserved
fragments with old trees. Trees along roads are locally very interesting, although air
pollution and especially the removal of Ulmus have strongly altered the lichen flora (Fig.
6). Semi-naturals habitats like the Mesobromion communities and heathlands are now
very reduced but nevertheless still shelter an interesting lichen flora.