An indirect gradient analysis of the ecological relationships between ancient and recent reiverine woodlands to the south of Bruges (Flanders,Belgium)

Summary Riverine forests to the south of Bruges were sampled according to the principles of the Braun-Blanquet approach. Cartographic data allowed a distinction between old (pre-1775) and recent (planted after 1775) woodland. Using a chi-square criterion and/or a Fisher exact probability test, the association of species with the two historical types of woodland was tested. Corylus avellana, Lamium galeobdolon, Primula elatior, Anemone nemorosa, Deschampsia cespitosa and Thamnium alopecurum are confined to ancient woodland. Glechoma hederacea, Prunus padus, Lysimachia nummularia, Ribes rubrum and Lychnis floscuculi have a significant affinity for recent woods.R-type prineipal components analysis produced an effective ordination of species and relevés. Interpretation of the scatter diagrams was performed using indicator values for the species and some environmental parameters for the relevés. Two major gradients were detected: the first one is the coenocline from wet, basic clay soils towards drier, more acidic, sandy soils. Anthropogenic dynamics, through the general management which effects the micro-climate in the wood, particularly the relative light intensity, has been recognized as the second ecological parameter.The potential natural vegetation of the valleys is thus determined primarily by soil texture and soil moisture, and secondarily by former land use (and age). It takes at least 200 years before old woodland species start to colonize recent woodland.We are much indebted to Prof. Dr. P. Van der Veken for his criticism of the manuscipt and to B. Kuziel en G. Dujardin for reviewing the English text.Nomenclature follows De Langhe et al. (1978) for vascular plants and Margadant (1973) & Margadant & During (1973) for bryophytes.Dedicated to the memory of Dr. Ir. G. Sissingh (1912–1979).This study was supported by a grant from the Instituut tot aanmoediging van het Wetenschappelijk Onderzoek in Nijverheid en Landbouw and since 1 October 1979 from the Nationaal Fonds voor Wetenschappelijk Onderzoek.