COS 244-4 - CANCELLED - Dynamics and drivers of tree growth and wood formation in an endangered light-demanding tree species from the tropical Africa

Abstract: Understanding the dynamics of tree growth and wood formation is of crucial interest to allow forecasting the response of terrestrial ecosystems to climate changes and other environmental variations. While tree-ring chronologies generally provide information on the interannual and multi-centennial trajectory of tree growth, it remains less clear when wood formation exactly takes place, how this timing of wood formation deviate from the timing of tree growth, how synchronized trees are in the timing of tree growth and wood formation and how sensitive the process of tree growth and wood formation is to photosynthesis and climate. In this study, we monitored tree-ring formation over 13 months in 5 trees of Pericopsis elata (Harms) Meeuwen (Fabaceae), a flagship semi-deciduous tree species of the African tropical forest. Therefore, we collected wood microcores monthly and used high-resolution X-ray computed tomography to unravel the timing (onset and cessation), duration and rate of wood formation. We additionally monitored tree growth over 13 months in 9 trees at a high temporal resolution (30 minutes interval) using point dendrometers coupled with a weather station and derived crown greenness of 5 additional trees over 36 months from imagery of timelapse cameras. The average duration of tree growth derived from dendrometers time series was 178 ± 48 days. Asynchronous tree growth was observed between trees, with varying onset and cessation timings. Similarily, the intra-annual trajectory of crown greenness showed to be asynchronuous between trees and between years. However, for a given tree, the peak of crown greenness occurs at the onset of tree growth and the lowest crown greenness is reached when tree growth slows down. This result suggests that despite its triggering effect on the onset of tree growth, the dynamics of leaf photosynthesis and tree growth are decoupled. The dynamics of tree growth showed to be tighly associated to climate and tree stature. At the wood level, the high-resolution X-ray computed tomography performed on microcores will allow deriving the timing and dynamics of wood formation. The processing of microcores is still ongoing at the laboratory of wood technology of Ghent University and the results will be shown at the conference. As one of the first attempts revealing the rhythms of tropical trees in the Congo Basin, results from this study provide useful insights for the management of Congo Basin forests in a changing environmental context.