(EFI) FlyForSIF will combine hyperspectral and solar-induced chlorophyll fluorescence airborne measurements to determine tree stress responses along a stress severity axis, to upscale current and possible future climate impacts on forests.

Extreme events in Europe have been shown to affect forest health status and they will likely increase in frequency, causing significant impacts. Super-sites integrating long-term ground observations and multi- scale spectral information need to be established across biogeographical regions, focusing on key forest types that have already shown significant degradation (such as evergreen and deciduous oak forests, and southern European pine forests). In this context, the FlyFor will combine hyperspectral and solar-induced chlorophyll fluorescence airborne measurements to determine tree stress responses along a stress severity axis, to upscale current and possible future climate impacts on forests.

A biogeographical west-European transect including three super-sites (in forest ecosystems which are showing mild to severe signs of decline) was designed including:

• Mediterranean evergreen oak forests,
• continental deciduous oak forests,
• ow altitude alpine pine forests.

Ground-truth data available at the selected super sites (Eddy Covariance, defoliation, sap flow, canopy hyperspectral reflectance and SIF) will be integrated with additional FlyForSIF measurements (airborne SIF, Leaf Area Index, Leaf Water Content, Specific Leaf Area, leaf pigment content and leaf Pulse-Amplitude- Modulation-PAM fluorescence). Pigments (including xanthophylls) will be measured at selected trees during the summer of 2025. Flight campaigns will be carried out with IBIS-CASI-SASI hyperspectral sensors. The ability of single-tree spectral information to detect tree stress will be tested and upscaled to the satellite level using PlanetScope imagery.

In the FORWARDS initiative context, the expected results will act as a proof of concept for the future implementation of a multi-scale tool for long-term detection of climate change impacts on European forests. europee.

FEM activity:

• Project coordination
• Acquisition of hyperspectral images and processing
• Support on ground measuremnts at the Bosco della Fontana site

(HEU Horizon Europe) Forests play a key role in the Earth climate system as they cover about 30% of the land area. In the last decade they absorbed more than 7 Gt of CO₂ contributing to reduce global warming and to buffer and mitigate increasing climate variability. The summers of 2018 and 2019 included some of the hottest and driest periods ever recorded globally, however the extent and severity of their impact is unknown due to lack of a comprehensive monitoring network, which generally does not include hard-to-reach areas characterised by strong logistic limitations.
Therefore, novel technological solutions are urgently needed to monitor forest responses to climate change and related extreme events also in remote areas. Recent advances in Internet Of Things technology (IoT), satellite IoT connectivity and energy harvesting systems are opening unprecedented opportunities for the use of IoT devices in standalone experimental setups.
In this context, the aim of the RemoTrees project is to design and build an innovative, autonomous in-situ monitoring system designed for remote forest areas and providing data via satellite communication to a dedicated RemoTrees platform. In this framework, RemoTrees will integrate existing and novel Earth Observation (EO) data with in-situ observations of Essential Climate Variables (ECVs: fraction of absorbed photosynthetically active radiation, leaf area index, soil moisture, biomass change) and other key variables including e.g. stem growth, stem moisture, sap flow, canopy transmittance, besides air humidity and temperature. RemoTrees will include study cases on interoperability with GEOSS (Global Earth Observation System of Systems), and on how in-situ data can support an improved understanding of the climate variability impact on forests. The reinforced in-situ component will be beneficial for Copernicus products validation and will enhance the assessment of climate change long-term mitigation and adaptation potential of forests, towards novel insights for climate-smart forest management.