The new geological map of Wallonia permits to obtain a more global view of the tectonic organization of the Palaeozoic terrains around the Variscan Front in southern Belgium. This zone oriented WSW-ENE and passing south of an axis Charleroi-Namur, was firstly highlighted by the coal mining works, but has been significantly documented notably through deep boreholes and seismic profiles. A coherent structural sketch of the Variscan Front is proposed for its entire longitudinal course, where the following structural units are distinguished, from north to south: the Brabant Massif and the base of the cover unaffected by the Variscan orogeny, the Brabant Parautochthon, the Haine-Sambre-Meuse Overturned Thrust sheets (HSM-OTS) and the Ardenne Allochthon. Undeformed terrains during Variscan event constitute the northern border of the Variscan Front. The Brabant Parautochthon includes Devono-Carboniferous terrains, which are folded and faulted. The HSM-OTS are formed by the superposition of several sheets (e.g. La Tombe sheet), which are supported by various thrust faults (e.g. Masse fault). The Ardenne Allochthon, which has been displaced during the Variscan orogeny, rests on the Brabant Parautochthon and the HSM-OTS through a faulted zone, which is locally known as the Midi Fault.
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In the mountain forests of the Kahuzi-Biega National Park (KBNP), in the Democratic Republic of Congo, where Sericostachys scandens, a woody climbing plant in the Amaranthaceae family, is expanding, trees appear to be negatively affected by this liana. In order to contribute to the understanding of the links between the expansion of the liana and the decline of its hosts, we compared the density and the species richness of the trees of dbh (diameter at breast height) ≥5 cm from the plots invaded by S. scandens with those from parcels that are still free from the invasion. The results of the paired unilateral t test applied to the overall sample showed that the tree density is very low in the plots dominated by the liana (p < 0.01), but that species richness is not affected (p > 0.05). In the class with diameter [10–30 cm], the lowest density of trees corresponds to the plots colonized by S. scandens, compared to the places where the liana is not abundant (p < 0.01). Further, the density of trees is significantly lower (p < 0.05) in the classes with diameters [5–10 cm] and ≥30 cm, in plots dominated by S. scandens. In conclusion, the emergence of the liana S. scandens has a negative effect on the density of the trees in the mountain forest of the KBNP. Résumé Dans les forêts de montagne du Parc National Kahuzi-Biega (PNKB), en République Démocratique du Congo, où Sericostachys scandens, plante ligneuse grimpante de la famille des Amaranthaceae, est en plein essor, son feuillage dense encombre les arbres et les étouffe. En vue de contribuer à élucider les liens entre l’expansion de cette liane et le déclin de ses hôtes, la densité et la richesse spécifique des arbres ayant un dbh («diameter at breast height», c’est –à –dire le diamètre mesuré à 1, 30 m au-dessus du sol) ≥5 cm des parcelles envahies par S. scandens ont été comparées à celles des endroits qui ne le sont pas. Le résultat du test t unilatéral par paires appliqué à l’échantillon global a montré que la densité des arbres est très basse dans les parcelles dominées par la liane (p < 0.01), mais qu’il n’y a pas d’effet sur la richesse spécifique (p > 0.05). Dans la classe de diamètre [10–30 cm[, une densité plus faible a été trouvée dans les parcelles colonisées par la liane par rapport à celles où elle n’abonde pas (p < 0.01). En plus, la densité des arbres est significativement basse (p < 0.05) dans les classes de diamètres [5–10 cm[et ≥30 cm dans les parcelles dominées par la liane. L’expansion de la liane S. scandens a donc un effet négatif sur la densité des arbres en forêt de montagne au PNKB.
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