Martin Tanghe

Ecological amplitude in Silene nutans in relation to allozyme variation at the western margin of its distribution

. At the western border of its geographical range, Silene nutans (Caryophyllaceae) has evolved two groups of parapatric populations showing distinct allozyme patterns and apparently occurring on different bedrock types. This study tests the hypothesis that these groups represent edaphic ecotypes. With this in view, the ecological amplitude of 36 populations of Silene nutans from Belgium was investigated and their synecology specified using vegetation composition and soil parameters; Ellenberg indicator values were used for ecological interpretation of the vegetation analyses. The results provide evidence that allozyme and habitat variations are correlated, the two groups occurring on contrasting soil with distinct vegetation types. One group is restricted to alkaline soils and typically occurs in open calcareous grasslands, fringes and scrub. The other group is characterized by wider autecological and synecological ranges with a bimodal pH- distribution, occurring on two kinds of siliceous soils: (1) neutral soils, supporting vegetation with a high species richness comprising many mesophilous species, and (2) CaCO3 -free bedrocks characterized by acidophilous, species-poor, open dry grasslands and woodlands. It also appears that factors not related to soil chemistry, such as microclimate, are involved in the ecological specialization of the two ecotypes. It is argued that these ecotypes exemplify adaptive radiation and parapatric speciation at the margin of a species distribution area.

Valeur des coupes à blanc de pessières pour la conservation de la biodiversité en Wallonie; restauration de milieux semi-naturels à partir du stock grainier du sol

Abstract Utilisation of Norway spruce (Picea abies) for the valorisation of unproductive land in the Walloon region (southern Belgium) during the second half of the XIXth century has caused dramatic loss of biodiversity. However, it preserved some areas from the general eutrophication due to agriculture intensification. We investigated the reconstituting vegetation on clearcuts of 25 to 50 year old plantations. Vegetation composition is widely in accordance with past extensive land use before Norway spruce plantation and characteristic species are generally well represented. Best-conserved habitats are Calluna heathlands and acidic mires. We also examined the persistent soil seed bank in three standing plantations. Species present in these seed banks are nearly the same as those found in situ in clearcuts. So the potential of these new environments is high in terms of nature restoration and conservation.