Beyond 30 years comprehensive observations on forest ecosystem functioning in changing climate

Life on Earth, the biosphere, interacts closely with the atmosphere, hydrosphere, and soils, and is sensitive to changes in their composition and functioning. These interactions take place on spatial scales from nanometers to global, and time scales from nanoseconds to millennia (Wanner 2008, Kulmala 2014). Changes in any of these components affect the others via material and energy flows, various linked processes and complex feedbacks. This implies the systems should not be observed in isolation, but rather with a comprehensive and holistic concept (Kulmala 2018). Current Earth system models underestimate these feedbacks (Stevens et al. 2024). One reason for this is that the Earth observations are traditionally fragmented, too scarce, and focus on single discipline. To be able to study complicated interactions, both sudden and subtle process changes and diverse feedbacks between different Earth components, and to foresee changes in the Earth system, a holistic, interdisciplinary approach is needed (Kulmala 2018). Here, we present a holistic observation concept implemented in a boreal forest ecosystem over 30 years with continuous measurements of atmospheric and ecosystem variables. This SMEAR concept is based on comprehensive, multi-scale and continuous long-term observations (Hari and Kulmala 2005; Hari 2016). It has been developed to meet environmental grand challenges and to collect big open data sets to test theories and develop multi-scale models at the interfaces of different Earth components. Such unique environmental open data can contribute to solving burning questions of society – even questions that are currently unforeseen. The concept connects forest ecology with soil sciences, atmospheric sciences and hydrology, and allows studies on seasonal variations of trace gases, atmospheric aerosols, greenhouse gases, and meteorological variables, along with the long-term trends in ecosystem functions and interactions, and integration of data from satellites, models and in-situ observations (e.g., Neefjes 2022, Vesala et al. 2022, Kulmala et al. 2023, Aslan et al. 2024, Zhang et al. 2025, de Quesada 2025). The 30-year period covers both a climate warming trend (CO2 and temperature increase) and active forest management, which are reflected e.g. in ecosystem carbon sink, trace gas exchange, and atmospheric aerosol formation. In the presentation, the concept and examples of short-term and long-term observations are presented, and the significance of open data is highlighted.