| Increasing droughts and heatwaves worldwide have been threatening the global ecosystems including those in Sweden. The severe 2018 summer drought in Sweden has severely affected Sweden's forests such as forest functioning and productivity, posing an important challenge to the forest's resilience under future climate change. The question if Sweden's forests are able to adapt to a rapidly changing climate, and can still maintain the overall functioning (e.g., transpiration and the carbon uptake ability) and ecosystem services (e.g., biomass production) which are valuable to both Swedish society and the regional climate system, remains largely unclear. This project aims to facilitate the assessment of Swedish forest resilience under changes in future climate extremes by making use of the recently available in-situ measurement of hydraulic variables, including the whole-tree sap-flow measurements in the research stations of ICOS-Sweden and SITES, for ecosystem modelling studies. We will combine the use of other materials and methods, including in-situ field measurement of meteorological and ecosystem status, high-resolution satellite-based remote sensing image (e.g., from Sentinel 2), and high-resolution ecosystem modelling to investigate three research questions closely related to Swedish forest resilience: 1) How do heat and droughts induce losses of plant hydraulic functioning along soil-plant-atmosphere continuum (SPAC) for Swedish forest?. and 2) How do changes in SPAC dynamics affect the overall ecosystem productivity, composition and functioning, and carbon and water exchanges? 3) Can we improve the understanding of future changes in Swedish ecosystem resilience under anthropogenic warming? The proposed project will be running for two years bringing together forest ecologists, experts in ecological measurements in ICOS-Sweden and SITES, and ecosystem and climate modellers.
Our preliminary analyses suggest a dramatic decrease in whole-tree transpiration during 2018, and a clear distinction of a functional relationship between surface conductance and Bowen ratio at the ecosystem level, with a stronger control of surface conductance under the 2018 droughts compared to the non-droughts years. They imply that changes in forest properties were large enough to modulate the efficiency of land-atmosphere interaction (e.g., through water and carbon exchanges in SPAC), thus likely affecting ecosystem productivity in the following years, and the overall forest vulnerability to climate in a longer period.
The proposed project will improve our understanding of Swedish forest resilience under the expected increase in future climatic extremes. It will directly fit into the research theme of “Plant health” defined by the foundation. Specifically, the improved understanding of changes in forest transpiration under heatwaves and droughts in Sweden will help fill the knowledge gap of plant’s physiological response to short-term extreme growing conditions, which is vital to advance the understanding of tree mortality and recovery for the high-latitude regions. It also has a natural link to Sweden’s Environmental Objects, the Swedish Forestry Act, U.N.’s Convention on Biodiversity and U.N.’s Sustainable Development Goals.
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