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.
Located in
Library
/
RBINS Staff Publications
This study deals with the relation between tropical meiofauna and environmental variables by comparing the 'benthic' (i.e. in the bare sediment adjacent to seagrass plants) and the 'epiphytic' (i.e. in samples including seagrass plants) meiofauna associated with five seagrass species from the high intertidal to the high subtidal zone in Gazi Bay (Kenya), Ordination and variance analysis revealed three distinct 'benthic' and two 'epiphytic' meiofauna assemblages. These assemblages corresponded entirely with those identified for the seagrass species: a high intertidal pioneer association (Halophila ovalis/Halodule wrightii), an intertidal climax assemblage (Thalassia hemprichii) and a high subtidal pioneer association (Halophila stipulacea/ Syringodium isoetifolium). These data support the hypothesis that meiofaunal communities correspond to the characteristic zonation of the seagrass vegetation in Gazi Bay. In beds of the pioneer seagrass species, the close relationship between sediment characteristics and both 'benthic' and 'epiphytic' meiofauna communities suggests that these pioneer communities were mainly driven by physical factors. The 'benthic' communities adjacent to the climax seagrass species T. hemprichii were more structured by biogenic factors, e.g. \% TOM, chlorophyll a and c, fucoxanthin, habitat complexity and growth form of the seagrass species. For its associated 'epiphytic' meiofauna the latter conclusion was even more striking. These data corroborate the importance of physical factors in disturbed environments (intertidal zone, near pioneer seagrasses) and of biotic factors in more stable conditions (subtidal zone, near climax seagrasses). © 2001 Elsevier Science B.V.
Located in
Library
/
RBINS Staff Publications
