Mesoscale transect sampling of trees in the Lomako-Yekokora interfluvium, Democratic Republic of the Congo

We conducted a mesoscale transect sampling of trees greater than or equal to 10 cm DBH in the Lomako Yekokora interfluvial forest, Democratic Republic of the Congo. Our objective was to characterize the forest landscape contained between the Lomako and Yekokora rivers in terms of its floristic composition and to investigate how representative the Lomako study site, the location of a long-term study of primates, was of the entire forest block. Fifteen transects were laid out at seven sample stations placed approximately 10 km apart and alongside a 70 km trail running from the Lomako study site to the margins of the Yekokora river. Three transects totaling 3.65 ha were laid out at the Lomako study site and two transects totaling 2 ha at each of the remaining six sample stations, amounting to 15.65 ha in total. Average DBH, tree density, tree species richness and floristic composition were determined for each transect. There were 5353 trees greater than or equal to 10 cm DBH in the total sample, representing 150 species in 35 families. Caesalpinoideae trees dominated the sample, followed by Olacaceae and Annonaceae. Four forest types were identified: mixed primary (57% of the sampled plots), secondary forest (9%), Gilbertiodendron (22%), and swamp (12%). The seven sample stations differed from each other in average DBH, tree density, tree species richness and floristic composition. Most of the difference, however, was due to the fact that the four forest types were not equally represented at each sample station. When forest types were contrasted independently, a marked difference in average DBH, tree density, tree species richness and floristic composition was recorded. Conversely, when only mixed primary forest was analyzed across the sample stations, no significant difference was detected except for average DBH. Thus the Lomako study site is representative of the forest landscape contained between the Lomako and Yekokora rivers only when the different forest types are treated separately. The sample stations ( including Lomako) differ from each other, however, in the proportional contribution of each forest type.