Search

Introduction: The Congo Basin forests, a crucial global carbon sink, are expected to face increased challenges of climate change by 2027, with an expected temperature rise of 1.5°C above pre-industrial levels, accompanied by increased humidity conditions. However, studies that try to understand their functioning and untangle the species-specific responses about how weather conditions impact secondary growth dynamics are still rare. Methods: Here we present the results of a study on diel and annual stem growth in 17 trees, belonging to 11 most abundant species, both canopy and understory, in the Mayombe forest (Congo Basin) in the Democratic Republic of the Congo (DRC). We measured highly-resolved radial stem size variations and weather conditions, to comprehend the ongoing patterns of secondary growth and examine the potential influence of projected weather conditions on them. Results: We found that at the diel scale, trees probably grow mainly from 6pm to 9am, and that at the annual scale, they grow mainly during the rainy season, from October to May. Some trees grow year-round, while others stop growing for a period ranging from 1 to 4 months. This growth cessation typically occurs during the dry season from June to September. A generalized linear mixed-effect model revealed that annual radial stem growth is positively related to rainfall. Discussion: Our results suggest that trees in the study site have a significant potential to cope with the projected 1.5°C increase in global temperature and an additional 50 mm of local rainfall. Trees of the species T. superba exhibited improved growth under the projected scenarios. For the other tree species, no significant difference in growth was observed between the predicted and observed scenarios. We believe that much remains to be done to better understand the tree growth-climate interaction of the large variety of tree species in the Congo Basin. [ABSTRACT FROM AUTHOR]

Plant functional traits have shown to be relevant predictors of forest functional responses to climate change. However, the trait-based approach to study plant performances and ecological strategies has mostly been focused on trait comparisons at the interspecific and intraspecific levels. In this study, we analyzed traits variation and association at the individual level. We measured wood and leaf traits at different height locations within the crown of five individuals of Pericopsis elata (Harms) Meeuwen (Fabaceae) from the northern tropical forest of the Democratic Republic of the Congo. All traits varied between and within individuals. The between-individual variation was more important for leaf traits (23%–48%) than for wood traits (~10%) where the within-individual variation showed to be more important (33%–39%). The sample location height within the crown was found to be the driving factor of this within-individual variation. In a gradient from the base to the top of the crown, theoretical specific hydraulic conductivity and specific leaf area decreased while the stomatal density increased. We found significant relationships among traits and between wood and leaf traits. However, these relationships varied with the position within the crown. The relationship between vessel size and vessel density was negative at the bottom part of the crown but positive upward. Also, the negative relationship between stomatal density and stomatal size became stronger with increasing height within the crown. Finally, the positive relationship between specific leaf area and theoretical specific hydraulic conductivity became stronger in higher parts of the crown, suggesting that P. elata constantly adapts its water use with respect to its water supply, more strongly at the top of the crown where the environment is more extreme and less buffered against environmental fluctuations. [ABSTRACT FROM AUTHOR]