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Modelling Forest Carbon Stocks, Fluxes and Forest Risks under Future Climate Scenarios (MODFLUX)

Domestic project

PROGRAMME: HRZZ Research Projects

STATUS: Ongoing
Project start: 01. Feb 2020.
Project end: 31. Jan 2024.
Contract body: Croatian Science Foundation



Climate change will affect forests, but tools which would facilitate risk assessment and informed decision making, based on understanding undelaying biogeochemical processes in forests, currently do not exist in Croatia. MODFLUX aims at providing climate change equipped modelling framework that is adapted for national forest ecosystems and environmental conditions. Using a model‑data‑fusion (MDF) technique, through an iterative and interactive process of comparison of model results and measured data, continuous adjustment of model parameters, and possible modification of the model, we will calibrate and validate a process-based biogeochemical model Biome-BGCMuSo for main national forest ecosystems. In MDF we will use two existing independent datasets which will be expanded with additional data from new field measurements. First dataset is a high-frequency eddy covariance (EC) data of CO2 fluxes at forest experimental station in Jastrebarsko, which is operational since 2008. Second dataset is spatially-explicit database on above and belowground forest ecosystem variables (i.e. wood biomass increment obtained from tree-rings, carbon stocks in forest floor and soil, fine root biomass) collected at 250 plots distributed throughout Continental, Alpine and Mediterranean regions of Croatia. Using future climate scenarios calibrated model will yield with improved capacity for the assessment of climate change impact on different forest types. Estimated changes in soil carbon stocks, obtained within MODFLUX, would be available for consideration in Croatia’s GHG reporting. By estimating forest fire risks under future climate scenarios MODFLUX will be the first to provide, to the policymakers and to the general public, a notion of the expected future fire risks in forest-rich parts of Croatia which are currently not affected by forest-fires. Overhaul of the existing EC station will ensure the continuation of the internationally unique research of CO2 fluxes in periodically flooded, pedunculate oak forest. Project results will be published in high impact factor journals and data collected within the project will be uploaded to open-access scientific databases.


Research station for monitoring carbon dioxide (CO2) fluxes between the forest and the atmosphere

Measurement station for monitoring CO2 fluxes was set up on 21st of September 2007 and since then it continuously measures and stores data on CO2 fluxes between the forest and the atmosphere. The measurements are based on the micro-meteorological method of eddy covariance (EC) and the station is registered within the European flux network under acronym HR-Jst (45°37’10’’ N, 15°41’16’’ E). With the EC system we determine the Net Ecosystem Exchange of CO2 between the forest and the atmosphere. The negative NEE value means that the amount of carbon removed from the atmosphere and stored in the forest biomass is higher than the amount of CO2 respired back into the atmosphere.

Within the scientific research project MODFLUX at the end of the year 2021 an extensive overhaul of the EC station was carried out with the value of investment of approx. 400,000 HRK. It included replacement of old sensors and logging instruments and installation of a new solar system. Some of the new measurement instruments at the top of the station (anemometer and CO2/H2O analyser, pyranometer and thermometers), procured within the overhaul of the EC station financed by the project MODFLUX, can be seen on the pictures (below).

EC station tower on which new instruments, procured within the project, are installed and new solar system.
New CO2/H2O analyser with 3D anemometer (left) and temperature and relative air humidity sensor (right).

Modelling of forest carbon stocks and fluxes with Biome-BGCMuSo model

Biome-BGCMuSo (BBGCMuSo) is a new variant of the well-known process-based model Biome-BGC (Running & Hunt 1993). Its main improvement is a multilayer soil sub-model that allows a more accurate representation of soil profiles regarding soil texture and bulk density, which can contribute to the improvement of simulation of C and water fluxes(Hidy et al. 2016). 2016). Within the MODFLUX project, improvement of calibration and validation of the model is carried out with the use of measured data on EC station (above) and many other data collected or measured within the project (e g. carbon stocks in soil on nearly 300 plots throughout Croatia, performed laboratory analysis on carbon content in leaf, fruit and wood of various tree species, tree increments, etc.). The main focus is the modelling of carbon stock changes in the soil. First results are published by project associates in a scientific paper(Ostrogović Sever et al. 2021). 2021).

New threats and risks for the forests

A research on increase of forest fire risks, related to rising temperature and drought due to the climate change, and spread of pests such as oak lace bug (Corythucha arcuata, Say) is planned within the MODFLUX project. Forest fire risk is assessed with Fire Weather Index (FWI). In collaboration with Croatian meteorological and hydrological service (DHMZ) analysis of historical data of meteorological measurements in the period 1961.-2020. was performed and significant increase of forest fire risks is observed (picture below).

Fire weather index (FWI) for the period 1991-2020 has significantly increased compared to the period 1961-1990 in all parts of Croatia.

Infestation of oak lace bug (Corythucha arcuata, Say), a new invasive species that is spreading throughout oak forests in Croatia from the year 2013. (Hrašovec et al. 2013), has been investigated within the MODFLUX project, and the results are published in the scientific paper Kern et al. (2021). Invasive pests negatively affect tree growth, and one of dramatic examples is sessile oak acorn abscission on which oak lace bug probably had its contribution. By sucking leaf juices, lace bug damages leaf and thus reduces photosynthesis capacity which directly results in reduced CO2 absorption from the atmosphere and what could be observed on the measurements carried out within the EC station in Jastrebarski lugovi. Although the most reliable mean of determining the presence of a lace bug is to record them on the field, the real scale and intensity of caused damage can best be monitored with remote sensing. Using satellite recordings from MODIS sensor we mapped spreading of oak lace bug in Croatia and identified the probable initial origin of its infestation in Croatia.

Mapping of oak lace bug spread with satellite recording MODIS revealed probable initial origin of lace bug infestation – higway A3 rest stop Spačva.

New research directions

Dead wood is an important structural component of forest ecosystems(Harmon et al. 1986) 1986with two significant roles in the time of climate change; promoting forest biodiversity(Humphrey et al. 2004) 2004and carbon storage(Pan et al. 2011). 2011). Under UNFCCC and EU regulations, dead wood is considered as one of five carbon pools in forest ecosystems (IPCC 2006) for which it is mandatory to report on carbon stocks and carbon stock changes within national greenhouse gas inventory reports. In order to calculate carbon stocks in dead wood, dead wood conversion factors by decay classes are needed: density and carbon concentration. Within MODFLUX project sampling of dead wood was conducted on ten tree species distributed in three biogeographical regions: Continental, Alpine and Mediterranean. Research results could be used in the accounting of dead wood carbon stocks in future national greenhouse gas inventory reports of Republic of Croatia.

Decay classes of dead wood (Pinus pinaster Aiton) from first to fourth decay class

Scientific papers

Kern, A., Barcza, Z., Hollós, R., Birinyi, E. & Marjanović, H., 2022. Critical Climate Periods Explain a Large Fraction of the Observed Variability in Vegetation State. Remote Sensing, 14 (21), 5621, 27. https://doi.org/10.3390/rs14215621

Kern, A., Marjanović, H., Csóka, G., Móricz, N., Pernek, M., Hirka, A., Matošević, D., Paulin, M., Kovač, G., 2021. Detecting the oak lace bug infestation in oak forests using MODIS and meteorological data. Agricultural and Forest Meteorology 306, 108436. https://doi.org/10.1016/j.agrformet.2021.108436

Ostrogović Sever, M. Z., Barcza, Z., Hidy, D., Kern, A., Dimoski, D., Miko, S., Hasan, O., Grahovac, B., Marjanović, H., 2021. Evaluation of the terrestrial ecosystem model Biome-BGCMuSo for modelling soil organic carbon under different land uses. Land (Basel) 10 (9), 968-968. https://doi.org/10.3390/land10090968

Nussbaumer, A., Gessler, A., Benham, S., de Cinti, Bruno., Etzold, S., Ingerslev, M., Jacob, F., Lebourgeois, F., Levanic, T., Marjanović, H. et al., 2021. Contrasting resource dynamics in mast years for European beech and oak — a continental scale analysis. Frontiers in Forests and Global Change 4, 689836. https://doi.org/10.3389/ffgc.2021.689836

Presentations at scientific conferences

Ostrogović Sever, M. Z., Dimoski, D., Anić, M., Marjanović, H., 2021. Forest fine root biomass and soil CNP stoichiometry across three different biogeographical regions in Croatia. EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13723. https://doi.org/10.5194/egusphere-egu21-13723

Bitunjac, D., Ostrogović Sever, M. Z., Sever, K., Marjanović, H., 2022. Coarse woody debris density and elemental components by decay classes for ten tree species in Croatia. EGU General Assembly 2022, Vienna, Austria/online, 23–27 May 2022, EGU22-11298. (pdf) https://doi.org/10.5194/egusphere-egu22-11298

Alberti, G., 2022. Linking tree species richness and functional diversity to the carbon cycle in the context of climate change. Natural resources, green technology and sustainable development/4-GREEN2022, Zagreb, Croatia, 14–16 September 2022. (pdf)

Marjanović, H., Anić, M., 2022. Challenges in long term monitoring CO₂ fluxes: The case of Jastrebarsko oak forest. Natural resources, green technology and sustainable development/4-GREEN2022, Zagreb, Croatia, 14–16 September 2022. (pdf)

Bitunjac, D., Ostrogović Sever, M. Z., Sever, K., Marjanović, H., 2022. Density and carbon concentration of downed dead wood by decay classes for ten tree species in Croatia. Natural resources, green technology and sustainable development/4-GREEN2022, Zagreb, Croatia, 14–16 September 2022. (p df)

Kern, A., Dobor, L., Hollós, R., Marjanović, H., Torma, C. Z., Kis, A., Fodor, N., Barcza, Z., 2022. Climate data for 1951–2100 for scientific, societal and policy purposes in Central Europe: the FORESEE database. Natural resources, green technology and sustainable development/4-GREEN2022, Zagreb, Croatia, 14–16 September 2022. (pdf)

Merganičová, K., Merganič, J., 2022. Modelling ecosystem dynamics under changing environmental conditions. Natural resources, green technology and sustainable development/4-GREEN2022, Zagreb, Croatia, 14–16 September 2022. (pdf)

Ostrogović Sever, M. Z., Bitunjac, D., Marjanović, H., 2022. Soil organic carbon modelling in Croatia: needs and challenges. Natural resources, green technology and sustainable development/4-GREEN2022, Zagreb, Croatia, 14–16 September 2022. (pdf)

Presenting in the media

Marjanović, H., 31.03.2022. TV show “Klimatska budućnost”, N1 television. https://hr.n1info.com/video/n1-info/n1-klimatska-buducnost-31-3-2022/