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AbstractLianas are poorly characterized for central African forests. We quantify variation in liana composition, diversity and community structure in different forest types in the Yangambi Man and Biosphere Reserve, Democratic Republic of Congo. These attributes of liana assemblages were examined in 12 1‐ha plots, randomly demarcated within regrowth forest, old growth monodominant forest, old growth mixed forest and old growth edge forest. Using a combination of multivariate and univariate community analyses, we visualize the patterns of these liana assemblage attributes and/or test for their significant differences across forest types. The combined 12 1‐ha area contains 2,638 lianas (≥2 cm diameter) representing 105 species, 49 genera and 22 families. Liana species composition differed significantly across forest types. Taxonomic diversity was higher in old growth mixed forests compared to old growth monodominant and regrowth forests. Trait diversity was higher than expected in the regrowth forest as opposed to the rest of forest types. Similarly, the regrowth forest differed from the rest of forest types in the pattern of liana species ecological traits and diameter frequency distribution. The regrowth forest was also less densely populated in lianas and had lower liana total basal area than the rest of forest types. We speculate that the mechanism of liana competitive exclusion by dominant tree species is mainly responsible for the lower liana species diversity in monodominant compared to mixed forests. We attribute variation in liana community structure between regrowth and old growth forests mostly to short development time of size hierarchies.

Significance The responses of tropical forests to heat and drought are critical uncertainties in predicting the future impacts of climate change. The 2015–2016 El Niño Southern Oscillation (ENSO) resulted in unprecedented heat and low precipitation across the tropics, including in the very poorly studied African tropical forest region. We assess African forest ENSO responses using on-the-ground measurements. Across 100 long-term plots, record high temperatures did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality. Overall, despite the climate anomaly, forests continued to gain live biomass over the ENSO period. Our analyses, while limited to African tropical forests, suggest that they may be more resistant to climate extremes than Amazonian and Asian forests.

Tropical montane forests provide an important natural laboratory to test ecological theory. While it is well-known that some aspects of forest structure change with altitude, little is known on the effects of altitude on above ground biomass (AGB), particularly with regard to changing height-diameter allometry. To address this we investigate (1) the effects of altitude on height-diameter allometry, (2) how different height-diameter allometric models affect above ground biomass estimates; and (3) how other forest structural, taxonomic and environmental attributes affect above ground biomass using 30 permanent sample plots (1-ha; all trees ≥ 10 cm diameter measured) established between 1250 and 2600 m asl in Kahuzi Biega National Park in eastern Democratic Republic of Congo. Forest structure and species composition differed with increasing altitude, with four forest types identified. Different height-diameter allometric models performed better with the different forest types, as trees got smaller with increasing altitude. Above ground biomass ranged from 168 to 290 Mg ha-1, but there were no significant differences in AGB between forests types, as tree size decreased but stem density increased with increasing altitude. Forest structure had greater effects on above ground biomass than forest diversity. Soil attributes (K and acidity, pH) also significantly affected above ground biomass. Results show how forest structural, taxonomic and environmental attributes affect above ground biomass in African tropical montane forests. They particularly highlight that the use of regional height-diameter models introduces significant biases in above ground biomass estimates, and that different height-diameter models might be preferred for different forest types, and these should be considered in future studies.

Street trees are always considered a vital part of urban green infrastructure in urbanized areas through mitigating the negative effects caused by urbanization taking part in human well-being. However, little is still known about their diversity, structure and protection, mostly in Lubumbashi city in the Democratic Republic of the Congo (DR Congo), where the pace of urbanization is not only rapid but also unplanned. In this study, using an inventory, we have characterized the diversity, structure and protection measures of street trees along a land-use planning gradient in Lubumbashi for both planned and unplanned neighborhoods. From the results, a total of 1596 trees were encountered, comprising 40 species, 33 genera and 17 families, mostly dominated by exotic species (65%). In addition, most of the studied trees (63%) belonged to four species only (Jacaranda mimosifolia, Leucaena leucocephala, Mangifera indica, and Acacia auriculiformis) with Leucaena leucocephala and Jacaranda mimosifolia being highly represented in unplanned and planned neighborhoods, respectively. The most abundant diameter classes in the planned neighborhoods were those with at most 10 cm against the classes larger than 50 cm in the planned neighborhoods. In both neighborhoods, trees with protection equipment represent less than 35%. Furthermore, in planned neighborhoods notably, nearly half of the observed equipment is in a good condition. Despite the benefits associated with street trees, there is a need to reduce the proportion of exotic tree species by planting native utilitarian tree species.

Xylogenesis is synchronous among trees in regions with a distinct growing season, leading to a forest-wide time lag between growth and carbon uptake. In contrast, little is known about interspecific or even intraspecific variability of xylogenesis in tropical forests. Yet an understanding of xylogenesis patterns is key to successfully combine bottom-up (e.g., from permanent forest inventory plots) and top-down (e.g., from eddy covariance flux towers) carbon flux estimates.Here, we monitor xylogenesis development of 18 trees belonging to 6 abundant species during 8 weeks at the onset of the rainy season from March to April 2022 in a semideciduous rainforest in the Yangambi reserve (central Democratic Republic of the Congo). For each tree, the weekly cambial state (dormant or active) was determined by epifluorescence microscopy.We find interspecific variability in the cambial phenology, with two species showing predominant cambial dormancy and two species showing predominant cambial activity during the monitoring period. We also find intraspecific variability in two species where individuals either display cambial dormancy or cambial activity. All trees kept > 60% of their leaves throughout the dry season and the monitoring period, suggesting a weak relationship between the phenology of the cambial and foliar. Our results suggest that individual trees in Yangambi asynchronously activate their cambial growth throughout the year, regardless of leaf phenology or seasonal rainfall.These results are consistent with global analysis of gross primary productivity estimates from eddy covariance flux towers, showing that tropical biomes lack a synchronous dormant period. However, a longer-term monitoring experiment, including more species, is necessary to confirm this for the Congo Basin. As Yangambi is equipped with facilities for microscopic wood analysis, a network of inventory plots and a flux tower, further research in this site will reveal how xylogenesis patterns drive annual variability in carbon fluxes and how ground-based and top-down measurements can be combined for robust upscaling analysis of Congo basin carbon budgets.