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3. Boer, Th. A. de and Ferrari, Th. J.: 1961, ?Agricultural and Pedological Indication of Grassland Vegetation Survey Units?, Neth. J. Agric. Sci. 9, 61?70.
4. Ellenberg, H.: 1974, ?Zeigerwerte der Gefässpflanzen Mitteleuropas?, Scripta Geobot. Göttingen 9, 1?97.
5. Kop, L. G.: 1965, ?Moisture Indication on Grassland by Vegetation and Soil: A Comparison of Maps?, Neth. J. Agric. Sci. 13, 6?20.