In a follow-up of De Wit’s (1976) inventory of epiphytic lichens in The Netherlands, c. 17% of the area covered in that study was re-inventoried, using a comparable method. A strong increase in species diversity became apparent, probably caused by a decrease in S02 concentration. In a comparison of various indicators for S02 concentration derived from the epiphytic vegetation (number of species per sample point and number of species per 5x5 km2, or composite measures based on multivariate statistics), the number of species per 5x5 km2 grid square had the strongest correlation with the measured S02 concentration. A second factor affecting epiphytic vegetation was the atmospheric NH3 concentration. High concentration of this compound caused a dominance of nitrophytic species. The rate of change in the epiphyte vegetation between 1988 and 1989 was consistent with the rate of decrease of the S02 concentration during the preceding 5 years.

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Acta botanica neerlandica

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Koninklijke Nederlandse Botanische Vereniging

H.F. van Dobben, & A.J. de Bakker. (1996). Re-mapping epiphytic lichen biodiversity in The Netherlands: effects of decreasing SO2 and increasing NH3. Acta botanica neerlandica, 45(1), 55–71.