Prospectives

Tiré de: Prospectives, vol. 6, no 4 (sept. 1970)Titre de l'écran-titre (visionné le 24 janv. 2013

Tree4flux Forecasting future forest dynamics by exploring climate-growth relationships in the Biosphere Reserve of Yangambi in the Democratic Republic of the Congo

Tropical forests hold a crucial role in the global carbon cycle. Despite their potential role in mitigating the evolution of the Earth system, they are threatened by climate change. In this context, assessing the carbon balance and the underlying phenomena is a key element in understanding and optimizing the management of tropical forests. At the forest scale, the carbon balance is commonly defined by fluxes, i.e., net primary productivity and respiration, exchanged between three main reservoirs: canopy, stems, and roots. The TREE4FLUX project aims to fill the gapsleft on these subjects for the first time in the forests of Congo Basin forests, by focusing research around the CongoFlux tower in the Yangambi Biosphere Reserve (DRC). The flux tower provides continuous measurements of greenhouse gas fluxes, such as CO2, using the Eddy Covariance approach. On-the-ground approaches through a network of multiple permanent inventory plots help define the processes underlying these fluxes. The combination of these strategies is promising to refine CO2 exchanges between vegetation and the atmosphere. This is essential because expected rising dry periods and temperatures are likely to alter forest dynamics by modifying growth patterns, and mortality risks. More specifically, wood formation, which is actively controlled by different climatic drivers, plays a significant role in carbon uptake by tree growth. But climate-growth relations remain elusive. Pursuing the characterization of forest dynamic components is therefore mandatory to better understand the ongoing changes

Unravelling the carbon cycle at the tree and forest scale : a TREE4FLUX initiative in Central African Tropical Forests

Tropical forests play an essential role in the carbon cycle. However, climate change threatens their ability to store carbon. Specifically, understanding the perturbation of climatic regimes on carbon uptake mechanisms is crucial. However, our knowledge concerning the spatial and temporal carbon distribution over trees and forests is limited, especially in the context of tropical forests of Central Africa. The TREE4FLUX project aims to fill these gaps for the first time in the forests of Congo Basin forests, by focusing research at different scales around the CongoFlux tower in the Yangambi Biosphere Reserve (DRC). On the forest ecosystem scale, carbon uptake can be monitored by measurements of CO2 exchanges between the atmosphere and the vegetation using the Eddy Covariance approach. Carbon assessments are also possible through tree-growth measurements within a network of permanent inventory plots. However, refining the carbon cycle at the tree scale requires a detailed study of the numerous inextricable metabolic processes that underlie tree growth, e.g. photosynthesis, wood formation, or respiration. Because they are largely controlled by various climatic drivers, climate-growth relationships over time remain hard to establish. The chronology of carbon uptake and attribution to the different mechanisms remain elusive preventing a grasp of the intra-annual variations of these periodic processes and their articulation over time. This is the case of xylogenesis or wood formation in which each phase is differently involved in the carbon cycle and sensitive to various climatic drivers. To understand the sensitivity of tree growth to climate, we need to untangle the cambium s role in wood formation. For that purpose, monitoring cambial phenology helps characterize the distribution, allocation, and short- and long-term carbon storage in woody material. While tree growth uptakes carbon, respiration releases carbon into the atmosphere at various levels. Heterotrophic and autotrophic respirations have a decisive role in the carbon cycle at the forest scale but face significant misunderstandings in this regard. To upscale our understanding from individual tree to forest scale, we imperatively need respiration monitoring in both living and decayed trees. This requires unravelling the metabolic processes driving both autotrophic and heterotrophic respiration, i.e. the tree growth and decayed process, respectively. Characterization of carbon fluxes according to an integrative approach over climatic variations is required to understand how environmental changes affect ecosystem dynamics and their ability to provide ecosystem services

The TREE4FLUX project: Monitoring woody productivity and respiration to track Congo Basin Forest Carbon Dynamics

Tropical forests play a crucial role in the global carbon cycle. Yet, climate change threatens their ability to take up and store carbon. Our understanding of the spatial and temporal carbon distribution in trees and forests remains limited regarding these perturbations, especially in the context of tropical forests of Central Africa. The TREE4FLUX project aims to address these gaps by conducting research at different scales around the CongoFlux tower in the Yangambi Biosphere Reserve (DRC) in the heart of the Congo Basin forests. At the forest ecosystem scale, carbon uptake can be monitored by measurements of CO2 exchanges between the atmosphere and the vegetation using the Eddy Covariance approach. Carbon assessments are also possible through tree-growth measurements within a network of permanent inventory plots. However, refining the carbon cycle at the tree scale requires a detailed study of the numerous metabolic processes that underlie tree growth, e.g. photosynthesis, wood formation, or respiration. Because they are largely controlled by various climatic drivers, it remains challenging to establish climate-growth relationships. The chronology of carbon uptake and attribution to the different mechanisms remain unclear and prevent the grasp of their periodic intra-annual variations. To untangle that problem, monitoring cambial phenology helps characterize the distribution, allocation, and short- and long-term carbon storage in woody material. While tree growth uptakes carbon, respiration and decomposition release carbon back into the atmosphere at various levels. Heterotrophic and autotrophic respirations have therefore a decisive role in the carbon cycle at the forest scale, but face significant misunderstandings in this regard. To enhance our understanding of the carbon dynamic from individual tree to forest scale, we urgently need respiration monitoring in both living and decayed trees. This requires unravelling the metabolic processes driving both autotrophic and heterotrophic respiration, i.e. the tree growth and decayed process, respectively. Characterization of carbon fluxes according to an integrative approach is required to refine forest dynamics models and improve our comprehension of global carbon dynamics

Asynchronous xylogenesis among and within tree species in the central Congo Basin

Background 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 interspecifc or even intraspecifc variability of xylogenesis in tropical forests. Yet an understanding of xylogenesis patterns is key to successfully com bine bottom-up (e.g., from permanent forest inventory plots) and top-down (e.g., from eddy covariance fux towers) carbon fux estimates. Methods 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 (cen tral Democratic Republic of the Congo). For each tree, the weekly cambial state (dormant or active) was determined by epifuorescence microscopy. Results We fnd interspecifc variability in the cambial phenology, with two species showing predominant cam bial dormancy and two species showing predominant cambial activity during the monitoring period. We also fnd intraspecifc 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 asynchro nously activate their cambial growth throughout the year, regardless of leaf phenology or seasonal rainfall. Conclusion These results are consistent with global analysis of gross primary productivity estimates from eddy covar iance fux towers, showing that tropical biomes lack a synchronous dormant period. However, a longer-term monitor ing experiment, including more species, is necessary to confrm this for the Congo Basin. As Yangambi is equipped with facilities for microscopic wood analysis, a network of inventory plots and a fux tower, further research in this site will reveal how xylogenesis patterns drive annual variability in carbon fuxes and how ground-based and top-down measurements can be combined for robust upscaling analysis of Congo basin carbon budgets. Keywords Cambial phenology, Tropical forest, Yangambi, Carbon storage, Congo Basi

Armand Fougnies, Mécène, Ministre d'Auguste, Protecteur des Lettres

Hicter M. Armand Fougnies, Mécène, Ministre d'Auguste, Protecteur des Lettres. In: L'antiquité classique, Tome 18, fasc. 1, 1949. pp. 211-212

Armand Fougnies, Mécène, Ministre d'Auguste, Protecteur des Lettres

Hicter M. Armand Fougnies, Mécène, Ministre d'Auguste, Protecteur des Lettres. In: L'antiquité classique, Tome 18, fasc. 1, 1949. pp. 211-212

Un Dimanche avec Simenon

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