THE DISTRIBUTION ATLAS OF PTERIDOPHYTES A ND PHANEROGRAMS OF SWITZERLAND (WELTEN AND SUTTER 1982) IN A RELATIONAL DATABASE - SPECIES NUMBERPER MAPPING UNIT AND ITS DEPENDENCE ON VARIOUS FACTORS

Wohlgemuth T., 1993. The distribution atlas of pteridophytes and phane rograms of Switzerland (Welten and Sutter 1982) in a relational databa se: Species number per mapping unit and its dependence on various fact ors. Bot. Helv. 103: 55-71. The distribution atlas of pteridophytes an d phanerograms of Switzerland (Welten and Sutter 1982) was digitized a t the Swiss Federal Institute for Forest, Snow and Landscape Research in Birmensdorf (CH). The data are stored in a relational data base, wh ich is flexible enough to allow any kind of retrieval and analysis. Th e floristic diversity and its dependence on various factors was analys ed by comparing the species number per mapping unit. A relation could be established between species numbers and the following factors: rang e of altitude covered by the mapping unit, rock type, geographical reg ion, and thoroughness of the mapping. Low species numbers were found i n most of the mountainous areas in the Ticino consisting mostly of non -calcareous rock, such as Gneiss. Analysis shows, that the species num bers in the western parts of the country are on average lower than in the eastern parts. The geographical regions with the highest floristic diversity are the Valais, the Ticino, the Grisons and the eastern par t of the Northern Alps. A link was found between the species number pe r mapping unit known from herbarium specimens only and the nearest her barium. The species number per mapping unit known from the literature strongly depends on the quality of the Flora available.