Multiple Stable Dominance States in the Congo Basin Forests

Abstract

Understanding the dynamics of dominant tree species in tropical forests is important both for biodiversity and carbon-related issues. We focus on the Congo Basin (East of Kisangani) to investigate the respective roles of topographic/soil gradients and endogenous dynamics in shaping local variations in dominance. We used a dataset of 30 1-ha plots, in which all trees above 10 cm diameter at breast height (DBH) were censused. Soil samples were analyzed for standard pedologic variables and a digital elevation model permitted to infer topography and hydromorphy. We found that this forest is characterized by variations in the abundance of three dominant species: Petersianthus macrocarpus (P.Beauv.) Liben (PM), Gilbertiodendron dewevrei (De Wild.) J.Leonard (GD) and Julbernardia seretii (De Wild.) Troupin (JS). These variations occur independently of substratum or topography variations. At plot level, the local relative abundance never reached 50%, the threshold for monodominance proposed in the literature, but rather progressively increased to reach higher values for canopy trees (>60 cm DBH), where this threshold could be exceeded. We found no sign of shifting compositional dynamics, whereby the dominant species would switch between the canopy and the undergrowth. Our results, therefore, support the possibility of the existence of stable dominance states, induced by endogenous processes, such as biological positive feedbacks fostering monodominance. We also document a strong relation between monodominance level and alpha diversity, when giving more weight to abundant species which is expected (R² = 0.79) but also when giving more weight to rare species (R² = 0.37), showing that monodominance influences tree species richness patterns. Structural differences existed between groups, with the PM group having more (and on average smaller) stems and lighter wood on average, but paradoxically also higher biomass and basal area.

Lomami Buffer Zone (DRC): Forest composition, structure, and the sustainability of its use by local communities

“…Although the southern part is the most accessible from Kindu, and therefore most likely to be more exploited than other parts of the Buffer Zone, further research is recommended in the central and northern parts, where floristic composition is likely to be different. For example, Julbernardia seretii which forms monodominant stands (Katembo et al, 2020) was not found in our study area, but this species was cited among the preferred trees for firewood by some communities living in the central part of Buffer Zone Batumike, Imani, Bisimwa, Mambo, et al, 2021). Secondly, we did not sample trees 10 cm diameter (juveniles and subadults) due to difficulties in seedling and sapling identification in the field Quantifying the level of utilization could help better understand the impacts of each type of usage and the combined effects of different usages (e.g., how debarking affects tree fruiting, and therefore, seeds available for regeneration).…”

Carbon of Chaillu forests based on a phytosociological analysis in Republic of Congo, more than meets the eye?

“…However, the woody component among the terra firme associations (A8-A12) showed more similarities, with differences often due to human disturbance level. Katembo et al (2020) (Kearsley et al, 2013).…”

The structure of Leguminosae-Detarioideae dominant rain forest in Korup National Park, Cameroon

“…The tree species composition in the cluster is comparable to that outside the cluster, except for the Detarioideae tree species that form the cluster, although the species diversity per surface area is lower in Detarioideae forest, especially for canopy tree species (Hart et al 1989;Makana et al 2011;Djuikouo et al 2014;Katembo et al 2020). Of the tree species ≥ 10 cm stem diameter found in the cluster, excluding Detarioideae, 82-87% occurred also in the Detarioideaepoor KFDP plot (Thomas et al 2003; estimated because some tree species were named to genus level only).…”

“…There are no significant changes in soil substrate, topography, or other environmental factors between the P group and the forest to the east and west of it that might account for the change in vegetation (Gartlan et al 1986;Newbery et al 1988Newbery et al , 1997. Soils of Detarioideae-rich forests are generally similar to those of adjacent mixed forests (Hart 1990;Katembo et al 2020). The Detarioideae tree species occurred in a complex configuration of groups, and the groups of the various species were separated, or overlapped partially (fig.…”