ERE1.3

There are many initiatives to re-wet drained nature or former agricultural land. These young wetlands provide a natural habitat for a range of endangered species, while serving as a natural climate buffer by retaining water, regulating air temperature, and sequestering CO₂ from the atmosphere. However, wetlands may also emit CH₄, which has a global warming potential (GWP) of about 30. Thus, all carbon fluxes need to be quantified in order to assess if, from a climate perspective, CO₂ uptake outweighs CH₄ emission.

To assess the net effect of young wetlands on Greenhouse Gas exchange, we study the CO₂ and CH₄ fluxes of two recently rewetted areas near Groningen, the Netherlands. The fluxes are measured directly using the Eddy Covariance (EC) technique on a moveable station, alternating between the two sites. Meteorological observations are performed at these stations as well, along with other supportive measurements such as soil/water temperature. The alternating time gaps are filled by interpolation based on observed ecosystem responses. Footprint analysis provides insight into the role of various vegetation types inside these swamps. The resulting carbon budgets provide insight into GHG exchange over typically small temporal and spatial scales.

The study also examines the feasibility of these moveable stations, as they may reduce the relatively high research costs of EC measurements. The data from moveable stations is reliable if the data is regular, as the time gaps are filled by interpolation. At this stage, the timeseries is too short to draw any conclusions upon the reliability of the data. However, the moveable stations appear to be feasible from a practical point of view, as the station can be relocated relatively easy within the time span of a day.

The first results suggest both substantial CO₂ uptake and CH₄ emissions but a full year of data was not collected yet. Observed exchange compares well to similar studies previously performed.  

Ultimately, annual budgets of the carbon exchange response will be correlated to weather conditions but also to hydrological measures such as water levels. This should allow extrapolation of the data, which may serve as a basis for policy makers to manage the carbon balance when re-wetting nature to achieve net mitigation of greenhouse warming potential.

How to cite: Kruijt, B., Berghuis, H., Biermann, J., Jans, W., Franssen, W., Nijhof, E., Peltenburg, A., Lettink, R., Jacobs, C., Hutjes, R., and Veraart, J.: Greenhouse gas exchange of young rewetted swamp in northern Netherlands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8483, https://doi.org/10.5194/egusphere-egu21-8483, 2021.

Although characteristics of the carbon balance and the organic carbon stock changes of arable lands have been the primary research focus of numerous studies, uncertainity is still a major factor in this area of research. Our aim is to determine the dynamics of carbon cycling in croplands in regards to a crop rotation consisting of different crop types and to clarify the factors driving the carbon fluxes between its main components.

A field-scale eddy covariance (EC) station was established in 2017 at a cropland site in Central Hungary in order to obtain the cropland’s annual net ecosystem exchange of CO₂ (NEE). Net ecosystem carbon budget (NECB) was calculated considering vertical and lateral C fluxes as well. Soil management is a conventional management with yearly deep ploughing and mineral fertilizer application.

During the three years of our experiment the crop rotation included winter wheat, winter rapeseed, sorghum and winter wheat. The largest net CO₂ uptake was observed during the sorghum season (from sowing to harvest, -309 g C m^-2 yr^-1). However, extreme autumnal drought resulted in the incomplete germination of rapeseed in 2018, which led to carbon loss (108 g C m^-2 yr^-1) during this vegetation period. Results show a significant difference between the two winter wheat seasons – sown in 2017 and 2019 – which can be explained by the differing precipitation of the two periods. Despite the strong CO₂ uptake of winter wheat and sorghum, NECB ranged between negligible C gain (-18.26 g C m^-2 year^-1, sorghum) to C losses of up to 108 g C m^-2 year^-1 (rapeseed). During three years the C loss was 420 g C m^-2 as C export through harvest and fallow periods counterbalanced the crops’ CO₂ uptake.

As a conclusion we can state this cropland could not sequester enough carbon to maintain the soil organic carbon pool and in order to reduce the risk of the depletion of soil carbon stock further efforts are needed in the field of soil management practices.

How to cite: De Luca, G., Balogh, J., Pintér, K., Fóti, S., Bouteldja, M., Malek, I., and Nagy, Z.: Soil carbon balance in Hungarian crop rotation systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10977, https://doi.org/10.5194/egusphere-egu21-10977, 2021.

Grasslands cover half of New Zealand’s land area, with much of it consisting of pastoral agriculture systems of varying intensity. Carbon fluxes from grazed pasture are thus a crucial part of the national carbon budget. We have used Biome-BGCMuSo v6 to model national CO₂ fluxes from grasslands, calibrated with eddy covariance measurements at grazed farms at various sites around the country. We discuss the challenges of scaling up site measurements to the national level and modelling the diversity of New Zealand's pastoral sector. Model outputs will subsequently be used as a prior estimate of CO₂ fluxes in an atmospheric inversion to obtain a total carbon budget for New Zealand as part of the CarbonWatch-NZ project.

How to cite: Keller, E., Graham, S., Hunt, J., Wall, A., Schipper, L., McMillan, A., Hidy, D., Barcza, Z., Bukosa, B., and Mikaloff-Fletcher, S.: Modelling carbon fluxes from New Zealand’s pastoral agriculture, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3641, https://doi.org/10.5194/egusphere-egu21-3641, 2021.

The quantification of the net carbon flux from land use and land cover changes (f_LULCC) is essential to understand the global carbon cycle, and consequently, to support climate change mitigation. However, large-scale f_LULCC is not directly measurable, and can only be inferred by models, such as semi-empirical bookkeeping models, and process-based dynamic global vegetation models (DGVMs). By definition, f_LULCC estimates between these two model types are not directly comparable. For example, transient DGVM-based f_LULCC of the annual global carbon budget includes the so-called Loss of Additional Sink Capacity (LASC). The latter accounts for environmental impacts on the land carbon storage capacities of managed land compared to potential vegetation which is not included in bookkeeping models. Additionally, estimates of transient DGVM-based f_LULCC differ from bookkeeping model estimates, since they depend on arbitrarily chosen simulation time periods and the timing of land use and land cover changes within the historic period (which includes different accumulation periods for legacy effects). However, DGVMs enable a f_LULCC approximation independent of the timing of land use and land cover changes and their legacy effects by simulations run under constant pre-industrial or present-day environmental forcings.

In this study, we analyze these different DGVM-derived f_LULCC definitions, under transiently changing environmental conditions and fixed pre-industrial and fixed present-day conditions, within 18 regions for twelve DGVMs and quantify their differences as well as climate- and CO₂-induced components. The multi model mean under transient conditions reveals a global f_LULCC of 2.0±0.6 PgC yr^-1 for 2009-2018, with ~40% stemming from the LASC (0.8±0.3 PgC yr^-1). Within the industrial period (1850 onward), cumulative f_LULCC reached 189±56 PgC with 40±15 PgC from the LASC.

Regional hotspots of high LASC values exist in the USA, China, Brazil, Equatorial Africa and Southeast Asia, which we mainly relate to deforestation for cropland. Distinct negative LASC estimates were observed in Europe (early reforestation) and from 2000 onward in the Ukraine (recultivation of post-Soviet abandoned agricultural land). Negative LASC estimates indicate that fLULCC estimates in these regions are lower in transient DGVM simulations compared to bookkeeping-approaches. By unraveling the spatio-temporal variability of the different DGVM-derived f_LULCC estimates, our study calls for a harmonized attribution of model-derived f_LULCC. We propose an approach that bridges bookkeeping and DGVM approaches for f_LULCC estimation by adopting a mean DGVM-ensemble LASC for a defined reference period.

How to cite: Obermeier, W. and the LASC task-force: Spatio-temporal comparison of different approaches to derive land use and land cover change emissions by models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9837, https://doi.org/10.5194/egusphere-egu21-9837, 2021.

The aim of this work was to make improved estimates of land-use change in the UK, using multiple sources of data. We applied a method for estimating land-use change using a Bayesian data assimilation approach. This allows us to constrain estimates of gross land-use change with national-scale census data, whilst retaining the detailed information available from several other sources. We produced a time series of maps describing our best estimate of land-use change given the available data, as well as the full posterior distribution of this space-time data cube. This quantifies the joint probability distribution of the parameters, and properly propagates the uncertainty from input data to final output. The output data has been summarised in the form of land-use vectors. The results show that we can provide improved estimates of past land-use change using this method. The main advantage of the approach is that it provides a coherent, generalised framework for combining multiple disparate sources of data, and adding further sources of data in future is straightforward.

How to cite: Levy, P. E.: A Bayesian data assimilation approach to estimating land-use change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15126, https://doi.org/10.5194/egusphere-egu21-15126, 2021.

Changes in carbon pools, land use and land-use change can be monitored based on field inventoried sampling units without using maps or remote sensing products. One way is to use a sampling framework. The framework can be based on a map, but the map does not necessarily need to be used for improving the estimates. The map can consist of a Member state’s total land and freshwater area. The sampling units can be distributed using a systematic grid with randomized location in the framework. A permanent design (the same sample units are re-inventoried in a periodic cycle) has been proven efficient when estimating change. Stratification into assumed homogenous strata is another way to further improve the accuracy of estimates. The distribution of sampling units can be spatially explicit (geo-referenced) in the sense that their locations are identified using GPS. This, combined with the permanent design, makes it possible to estimate both gross and net land use transfers in order to provide a land use matrix. The area-based sampling combined with the Horvitz and Thompson-estimator, makes a sampling unit representative of a certain area and all sample units together comprise the total land and freshwater area. This design makes it possible to match changes in carbon pools to land use and land-use change and to trace them back in time. 

We present a monitoring design based on the Swedish NFI and adapted to reporting under the UNFCCC/KP frameworks or the EU-regulation. Pros and cons are discussed and we compare with alternative designs (combining ground truth with remote sensing). Finally, we assess the accuracy of estimates of selected variables (sample and model errors).

How to cite: Petersson, H., Breidenbach, J., Ellison, D., Lundblad, M., and Appiah Mensah, A.: Monitoring changes in carbon pools matched to land use and land-use change based on field sampling measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16400, https://doi.org/10.5194/egusphere-egu21-16400, 2021.

Since the collapse of the Soviet Union and transition to a new forest inventory system, Russia has reported (FAO, 2014) almost no changes in growing stock (+1.8%) and biomass (+0.6%). Yet remote sensing products indicate increased vegetation productivity (Guay et al., 2014), tree cover (Song et al., 2018) and above-ground biomass (Liu et al., 2015). Here, we challenge the official national statistics with a combination of recent National Forest Inventory and remote sensing data products to provide an alternative estimate of the growing stock of Russian forests and assess the relative changes in the post-Soviet era. Our estimate for the year 2014 is 118.29±1.3 10⁹ m³, which is 48% higher than the official value reported for the same year in the State Forest Register. The difference is explained by increased biomass density in forested areas (+39%) and larger forest area estimates (+9%). Using the last Soviet Union report (1988) as a reference, Russian forests have accumulated 1163×10⁶ m³ yr^-1 of growing stock between 1988–2014, which compensates for forest growing stock losses in tropical countries (FAO FRA, 2015). Our estimate of the growing stock of managed forests is 94.2 10⁹ m³, which corresponds to sequestration of 354 Tg C yr^-1 in live biomass over 1988–2014, or 47% higher than reported in the National Greenhouse Gases Inventory (National Inventory Report, 2020).

Acknowledgement: The research plots data collection was performed within the framework of the state assignment of the Center for Forest Ecology and Productivity of the Russian Academy of Sciences (no. АААА-А18-118052590019-7), and the ground data pre-processing were financially supported by the Russian Science Foundation (project no. 19-77-30015).

How to cite: Schepaschenko, D., Moltchanova, E., Fedorov, S., Karminov, V., Ontikov, P., Santoro, M., See, L., Kositsyn, V., Shvidenko, A., Romanovskaya, A., Korotkov, V., Bartalev, S., Fritz, S., Shchepashchenko, M., and Kraxner, F.: New estimate of growing stock volume and carbon sequestration of Russian forests based on national forest inventory and remote sensing data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11217, https://doi.org/10.5194/egusphere-egu21-11217, 2021.

In a recent Nature article, the satellite-based Global Forest Change (GFC) map was used to estimate the yearly harvest area in each of the EU26-states over the period 2004 to 2018 (Ceccherini et al. 2020). Finland and Sweden were identified as the countries with the largest harvest increases and the biggest effect on the EU’s climate policy strategy. Here, we employ more than 45,000 field observations from the Finnish and Swedish national forest inventories as reference observations to analyze the accuracy of GFC data. We find that harvested area increases only marginally, if at all, after 2015. What did increase abruptly after 2015, however, was GFC’s sensitivity to detect harvested areas and thinnings.

The results of the Nature article are therefore a consequence of an inconsistent time series in GFC due to a change in the mapping algorithm or the sensor system and are thus both incorrect and misleading. The article is thus a good example for how wrong results based on satellite data can be, if no adequate estimators utilizing reference data are used.

References

Ceccherini, G. et al. Abrupt increase in harvested forest area over Europe after 2015. Nature 583, 72-77 (2020).

How to cite: Breidenbach, J., Ellison, D., Petersson, H., Korhonen, K., Henttonen, H., Wallerman, J., Fridman, J., Gobakken, T., Astrup, R., and Næsset, E.: No “Abrupt increase in harvested forest area over Europe after 2015” – How the misuse of a satellite-based map led to completely wrong conclusions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13243, https://doi.org/10.5194/egusphere-egu21-13243, 2021.

How to cite: Ellison, D., Breidenbach, J., Petersson, H., Korhonen, K. T., Henttonen, H., Wallerman, J., Fridman, J., Mensah, A. A., Gobakken, T., and Naesset, E.: Reversing the European Trend Toward a Declining Land Carbon Sink?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16261, https://doi.org/10.5194/egusphere-egu21-16261, 2021.

Long-standing debates over the benefits of forest conservation vs. those of substitution and forest resource use continue to occupy attention in Europe and beyond. Moreover, many argue the carbon sequestration benefits of standing forest are greater than those from forest resource use and replanting. To study this question, we generate long-term scenario analyses based on different forest management strategies in Sweden, in particular comparing increasing forest use and increasing land set-asides over 100, 200 and 500 year cycles. We find that the cost of increasing land set-asides is reflected in a significant loss of the carbon benefits created by forest use (substitution and carbon sequestration). We explain this outcome through the loss of additional growth that occurs as forest in land set-asides matures and eventually reaches a steady state. For the Swedish forest, these costs are significant and may amount to the loss (lost opportunity) of annually providing and additional -14 MtCO2e in net annual removals. The EU-based LULUCF carbon accounting framework, however, does not recognize this benefit and thus may effectively encourage land set-asides at the expense of real, measurable forest and forest resource-based climate change mitigation.

How to cite: Appiah Mensah, A., Petersson, H., Berndes, G., Egnell, G., Ellison, D., Lundblad, M., Lundmark, T., Lundström, A., Stendahl, J., and Wikberg, P.-E.: On the Role of Forestry in Climate Change Mitigation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16472, https://doi.org/10.5194/egusphere-egu21-16472, 2021.

With the advent of global warming, forests are becoming an increasingly important carbon sink that can mitigate the negative effects of climate change. An understanding of the carbon dynamics of forests is, therefore, crucial to implement appropriate forest management strategies and to meet the expectations of the Paris Agreement with respect to international reporting schemes. One of the most frequently used models for simulating the dynamics of carbon stocks in forests is the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3). We applied this model in our study to evaluate the effects of harvesting on the carbon sink dynamics in Slovenian forests. Five harvesting scenarios were defined: (1) business as usual (BAU), (2) harvesting in line with current forest management plans (PLAN), (3) more frequent natural hazards (HAZ), (4) high harvest (HH) and (5) low harvest (LH). The simulated forest carbon dynamics revealed important differences between the harvesting scenarios. Relative to the base year of 2014, by 2050 the carbon stock in above-ground biomass is projected to increase by 28.4% (LH), 19% (BAU), 10% (PLAN), 6.5% (HAZ) and 1.2% (HH). Slovenian forests can be expected to be a carbon sink until harvesting exceeds approximately 9 million m³ annually, which is close to the calculated total annual volume increase. Our results are also important in terms of Forest Reference Levels (FRL), which will take place in European Union (EU) member states in the period 2021-2025. For Slovenia, the FRL was set to –3270.2 Gg CO₂ eq/year, meaning that the total timber harvested should not exceed 6 million m³ annually.

How to cite: Mali, B., Jevsenak, J., and Klopcic, M.: The effect of harvesting on national forest carbon sinks up to 2050 simulated by the CBM-CFS3 model: a case study from Slovenia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13486, https://doi.org/10.5194/egusphere-egu21-13486, 2021.