Forests provide a wide range of ecosystem services and are considered a critical resource for mitigating climate change. Yet, we still do not fully understand, how trees function and how they respond to changes in their environment. As a consequence, the future growth and productivity of forests are uncertain. This interdisciplinary project brings together precise measurements of tree photosynthesis and growth with mechanistic modeling to provide deep insight in i) how trees invest resources in wood formation and ii) how this process changes with climate, stand characteristics, and management.


Trees produce sugars through photosynthesis in their leaves and transport these sugars down the stem, where they are used as building blocks to form new wood cells. This fundamental process is – even after decades of research – not fully understood. How big is the portion of photosynthesis that is used for growth? And how does this "carbon allocation" depend on climate, forest management or other factors? Answering these seemingly questions is challenging, yet vitally important to anticipate environmental change impacts on forest ecosystems and resources.

Importantly, we can only forecast future forest functioning and productivity, if we can mathematically describe the relevant processes that happen inside trees. For this, we need precise and highly resolved data on these processes, which are still not very common. A consequence is that current vegetation models can simulate the amount of carbon that forests invest in growth only roughly. This is problematic because these models play an important role in guiding political decisions related to climate change. Hence, there is urgent need to close existing knowledge gaps and provide a better scientific basis for predicting forest growth and carbon cycling in a warming world. This can only be achieved through interdisciplinary research initiatives like "Inside out".


The overall goal of "Inside out" is to better understand and quantify the growth and carbon allocation dynamics in temperate European forests, using a novel combination of precise observations and mechanistic model simulations. We pursue a bottom-up approach to be able to scale our findings from the cell to the tree level, then to the stand level, and ultimately across larger regions. The information gained along the way will i) enhance the scientific basis of wood formation processes, ii) contribute to improving carbon allocation schemes in vegetation models, and iii) provide forest managers with a refined estimate of intra- and inter-annual forest growth, and how it varies with climate, competition, or other factors.

Study areas and approaches

We need two types of information to quantify carbon allocation: how much carbon (i.e. CO2) enters the forest through photosynthesis, and how much the trees grow over a given time period. Precise measurements of CO2 uptake are only available at a small number of experimental forest sites, where so-called "flux-tower data" are available for the past ~20 years. This study focuses on three such sites located in Denmark, France, and Germany that are dominated by European beech (Fagus sylvatica), although existing data from additional flux-tower sites will also be considered.

At each site, we apply a novel combination of methods to quantify and reconstruct tree growth with precision. These include quantitative wood anatomy to measure cell properties and wood density, tree-ring data to assess annual radial growth, and terrestrial LiDAR to quantify the volume of each tree and the entire stand. By integrating these observations with flux-tower data, we can study carbon allocation dynamics both within and between years. To generalize our observations across larger regions, we will combine them with a new mechanistic model of individual tree growth and verify the resulting simulations at independent test sites in Poland. Bringing together these temporal, spatial, and mechanistic perspectives enables us to cover the range of scales over which trees are shaped by their environment.


Follow the progress of the project.


Meet the people involved in the project.

Flurin Babst

Project Leader

Flurin is a researcher at the Department of Ecology, W. Szafer Institute of Botany, Polish Academy of Sciences. He is also a guest scientist at the Swiss Federal Research Institute WSL. Flurin leads and coordinates all research tasks, mentors junior team members, and handles the dissemination and promotion of the project outcome.

Jingshu Wei

PhD student

Jingshu is a PhD student in Inside out. He studies tree growth at intra-annual time scales using methods of Quantitative Wood Anatomy. By integrating wood cell parameters with eddy-covariance data of carbon and water fluxes, Jingshu assesses carbon allocation dynamics in trees and combines this insight with ecophysiological modeling. Jingshu produces and publishes research outcome, and disseminates project results to scientific and public audiences.

Maria Karamihalaki

Adjunct PhD student

Maria is a PhD student at the Department of Ecology, W. Szafer Institute of Botany, Polish Academy of Sciences and a guest PhD student at the Swiss Federal Research Institute WSL. She integrates terrestrial LiDAR, satellite remote sensing and tree-ring data to quantify and reconstruct forest biomass at the site and landscape scales. In combination with mechanistic carbon modelling, these observations help advance our understanding of carbon allocation dynamics in temperate forests. Maria produces and publishes research outcome and disseminates project results to scientific and public audiences.

Grzegorz Krok

Adjunct PhD student

Grzegorz is a PhD student at the Forest Research Institute in Sękocin Stary, Poland. He specializes in the quantification of forest structure and biomass using terrestrial laser scanning and GIS applications. His ongoing work in Milicz forest (our primary validation site) offers important and valuable synergies with Inside out. We thus collaborate with Grzegorz on field work, data exploration, publication, and dissemination of our findings to our commercial partner State Forests Poland.

Georg von Arx


Georg is the leader of the Dendro Sciences Group at the Swiss Federal Research Institute WSL. His role in the project is to support and guide the wood anatomical analyses, provide access to his excellently equipped laboratory, co-supervise the PhD student and participate in data exploration and publication.

Christian Ginzler


Christian is the leader of the Remote Sensing Group at the Swiss Federal Research Institute WSL. He supports and guides the analysis of terrestrial LiDAR data from the core sites, provides access to computational resources and infrastructure, co-supervises the PhD student and participates in data exploration and publication.

Andrew Friend


Andrew is a reader at the Department of Geography at the University of Cambridge. His role in the project is to guide the simulations of forest ecosystem processes with a new mechanistic model that was developed in his lab. Andrew also participates in data exploration and publication.

Andreas Ibrom


Andreas is a senior researcher at the Department of Environmental Engineering at the Danish Technical University. He is also the PI of the flux-tower site in Sorø, Denmark. Andreas provides access to his long-term monitoring site and to auxiliary data from earlier projects. He also guides the analysis of eddy-covariance measurements and participates in data exploration and publication.

Krzysztof Stereńczak


Krzysztof is a senior researcher at the Forest Research Institute in Raszyn, Poland. He provides access to existing research plots and auxiliary data in Milicz forest, supports the fieldwork and guides the data collection of the PhD students, and participates in data exploration and publication.

Margaret Evans


Margaret is an Assistant Professor in the Laboratory of Tree-Ring Research at the University of Arizona. Her role in the project is to provide support and guidance to the research tasks related to ecological scaling and the projection of forest changes under climate warming. Margaret also advises students and participates in data exploration and publication.

Join us

Are you interested in our project? We are always open for discussion, suggestions, exchange and collaboration.


See the results of our work.

Klesse S, DeRose RJ, Babst F, Black BA, Anderegg LDL, Axelson J, et al. (2020) Continental-scale tree-ring-based projection of Douglas-fir growth: Testing the limits of space-for-time substitution. Global Change Biology, DOI: 10.1111/gcb.15170. View at publisher

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Reyer CPO, Gonzalez RS, Dolos K, Hartig F, Hauf Y, Noack M, et al. (2020) The PROFOUND Database for evaluating vegetation models and simulating climate impacts on European forests. Earth System Science Data 12: 1295-1320. View at publisher

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Peters RL, von Arx G, Nievergelt D, Ibrom A, Stillhard J, Trotsiuk V, Mazurkiewicz A, Babst F (2020) Axial changes in wood functional traits have limited net effects on stem biomass increment in European beech (Fagus sylvatica). Tree Physiology 40: 498–510. View at publisher

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Trotsiuk V, Hartig F, Cailleret M, Babst F, Forrester DI, Baltensweiler A, et al. (2020) Assessing the response of forest productivity to climate extremes in Switzerland using model-data fusion. Global Change Biology 26: 2463-2476. View at publisher

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Hudson AR, Alfaro-Sanchez R, Babst F, Belmecheri S, Moore DJP, Trouet V (2019) Seasonal and synoptic climatic drivers of tree growth in the Bighorn Mountains, WY, USA (1654-1983). Dendrochronologia 58: 125633. View at publisher

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Schurman J, Babst F, Björklund J, Rydval M, Bace R, Cada V, et al. (2019) The climatic drivers of primary Picea forest growth along the Carpathian arc are changing under rising temperatures. Global Change Biology 25: 3136-3150. View at publisher


This project is financed by the HOMING programme of the Foundation for Polish Science under the European Union Regional Development Fund, Measure 4.4 of the 2014-2020 Smart Growth Operational Programme.

Project value: 839 795 PLN / EU grant value: 839 795 PLN



Please do not hesitate to contact us with questions or comments.


W. Szafer Institute of Botany, Polish Academy of Sciences
Lubicz 46, 31-512 Kraków, Poland
PHONE: +48 12 42 41 770 / FAX: +48 12 42 19 790