Periodic Reporting for period 1 - TERRACARB (The fate of TERRestriAl forest CARBon from photosynthesis to structural biomass under climate change)
Période du rapport: 2022-09-01 au 2024-08-31
Forests play a major role in the global carbon cycle. They uptake carbon through photosynthesis, return much of it through respiration, and accumulate some fraction as structural biomass (Bst). The forest carbon sink offsets nearly 30% of anthropogenic carbon-dioxide emissions, with Bst being the primary contributor to this sink due to its slow rate of turnover (years to centuries). However, climate change is increasing the frequency and intensity of drought events and negatively impacting both photosynthesis and Bst. As these two processes are interconnected but independently modulated by environmental variables, it is imperative that we track the fate of forest carbon through its lifecycle from uptake to allocation. In TERRACARB, we will investigate the interactions between climate, photosynthetic carbon uptake, and carbon allocation to Bst during drought across spatial and temporal scales (tree to global; hourly to decadal). To do so we will use an innovative interdisciplinary approach that combines remote sensing, eddy covariance, tree-rings, and point dendrometer derived estimates of productivity. First, we will investigate the decrease in photosynthetic carbon uptake during atmospheric and hydrologic drought. Next, we will examine the mechanisms by which drought events leave behind ‘legacy effects’ of below normal carbon accumulation. Finally, we will use a network of point dendrometers to evaluate the relationships between photosynthetic carbon uptake, tree radial growth, hydration, and climate variables at sub-seasonal timescales (hourly to daily) at multiple eddy covariance sites across the world. The findings from TERRACARB will help us better predict how forests will continue to accumulate carbon in the face of climate change.
The principal scientific achievements of TERRACARB have been to identify critical temperature related tipping points related to forest ecosystems in the global carbon cycle (Rao et al. 2023 and Lenczner, Rao et al., under review), the higher sensitivity of forest carbon accumulation in trees to aridity relative to carbon assimilation which calls into question the highly optimistic scenarios of future carbon cycling that are based on carbon assimilation and not tree growth (Rao et al., to be submitted), and an impetus for the establishment of a global paired dendrometer-flux tower network that in the upcoming years will lead to more refined projections of the terrestrial carbon cycle, the component with the highest uncertainty in the global carbon cycle.
Results from TERRACARB were presented and disseminated 11 times at various national and international conferences as the lead/presenting author (co-author presentations excluded) and 12 times at invited lectures at universities across the world. These include prestigous conferences such as the European Geosciences Union (EGU) and American Geophysical Union (AGU) meetings that host more than 20,000 researcher. Sessions were also hosted on topics pertaining to TERRACARB at both conferecnes. The universities at which results were presented include among others the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Switzerland; École Polytechnique Fédérale de Lausanne (EPFL), Switzerland; Columbia University, USA; and University of California Davis; USA.
Results from TERRACARB were presented and disseminated 11 times at various national and international conferences as the lead/presenting author (co-author presentations excluded) and 12 times at invited lectures at universities across the world. These include prestigous conferences such as the European Geosciences Union (EGU) and American Geophysical Union (AGU) meetings that host more than 20,000 researcher. Sessions were also hosted on topics pertaining to TERRACARB at both conferecnes. The universities at which results were presented include among others the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Switzerland; École Polytechnique Fédérale de Lausanne (EPFL), Switzerland; Columbia University, USA; and University of California Davis; USA.
TERRACARB has significantly contributed to our state-of-the art understanding of the impacts of increasing heat and arid extremes on plant stress and in turn on global carbon cycling. While state-of-the-art earth system models do predict decreasing plant productivity under warm temperatures, they generally do not include information regarding the critical temperatures at with plant leaves cease to operate. TERRACARB presented a framework to do so. Additionally, the current generation of earth system models generally project increased terrestrial productivity in the future due to the carbon-dioxide (CO2) fertilization effect. However, we show in our upcoming manuscript that carbon accumulation in tree growth is much more sensitive to increased aridity (an impact of climate change) than photosynthesis.
Consequently, climate change may decrease the ability of ecosystems to accumulate carbon notwithstanding impacts on photosynthesis. Additionally, very few observations currently exsist for real time tree growth and forest carbon cycling. TERRACARB is filling this gap via the creation of a paired flux tower-dendrometer network and is enabling a better understanding of climate impacts on long term forest carbon storage.Thus TERRACARB has already and will continue to shine light on the critical need to include carbon sink processes in earth system models and better incorporate the importance of extreme temperatures in carbon cycling.
Consequently, climate change may decrease the ability of ecosystems to accumulate carbon notwithstanding impacts on photosynthesis. Additionally, very few observations currently exsist for real time tree growth and forest carbon cycling. TERRACARB is filling this gap via the creation of a paired flux tower-dendrometer network and is enabling a better understanding of climate impacts on long term forest carbon storage.Thus TERRACARB has already and will continue to shine light on the critical need to include carbon sink processes in earth system models and better incorporate the importance of extreme temperatures in carbon cycling.