ASSESSMENT CARBON IN COARSE WOODY DEBRIS OF OAK FORESTS IN UKRAINE

Розглянуто питання депонування вуглецю у грубому деревному детриті (ГДД) дубових лісів України. Мортмасу дубових насаджень, зокрема ГДД, в Україні вивчено недостатньо, саме тому потрібно оцінити її потенційні обсяги та обсяги депонованого у ній вуглецю. Для дослідження використано інформацію бази даних Виробничого Об'єднання "Укрдержліспроект" про 23 тис. таксаційних виділів, де у насадженнях дуба звичайного виявлено під час таксації сухостій та захаращеність (деревна ламань). Дослідні дані проаналізовано за адміністративними одиницями, класами бонітету та типами лісорослинних умов. Середня частка запасу сухостою та деревної ламані (захаращеності) від стовбурного запасу у корі – 6,1 % та 5,4 % відповідно. Загалом у сухостої та деревній ламані дібров України депоновано 830 Гг С та 227 Гг С відповідно – у сумі близько 0,8 % від потенційного резервуару біомаси усіх дубових лісів. Отримані результати свідчать про незначну роль ГДД у депонуванні дубовими лісами України вуглецю, зокрема, порівняно з дібровами Австрії, де груба мортмаса депонує близько 39 % вуглецю біомаси цих лісів. Встановлено щільність вуглецю на одиницю площі на рівні 0,27 кг C·м-2 – для сухостою та 0,24 кг C·м-2 – для деревної ламані. Обсяги депонованого вуглецю у дібровах України є потенційно більшими, оскільки під час лісовпорядкування враховано сухостій і захаращеність запасом на виділі тільки більше 5 м3·га-1.Рассмотрен вопрос депонирования углерода в грубом древесном детрите (ГДД) дубовых лесов Украины. Мортмасса дубовых древостоев, ГДД в частности, в Украине изучена недостаточно, поэтому нуждается в оценке ее потенциальных объемов и депонированного в ней углерода. Для этого использованы базы данных Производственного Объединения "Укргослеспроект" с информацией о 23 тыс. таксационных выделов, где в древостоях дуба обыкновенного имелись сухостой и захламленность (валеж). Исследовательские данные распределены по административным единицам, классам бонитета и типам лесорастительных условий. Среднее долевое участие сухостоя и валежа (захламленности) от запаса стволов в коре – 6,1 % и 5,4 % соответственно. В целом, в сухостое и валеже дубрав Украины депонировано 830 Гг С та 227 Гг С соответственно – в сумме около 0,8 % от потенциального резервуара углерода биомассы всех дубовых лесов. Полученные результаты свидетельствуют о незначительной роли ГДД в депонировании дубовыми лесами Украины углерода, в частности, сравнительно с дубовыми древостоями Австрии, где грубая мортмасса депонирует около 39 % углерода биомассы этих насаждений. Установлена плотность углерода на единицу площади на уровне 0,27 кг C·м-2 – для сухостоя и 0,24 кг C·м-2  - для валежа. Объемы ГДД в дубравах Украины потенциально больше, поскольку во время лесоустровства были учтен запас сухостоя и валежа на выделе только более 5 м3·га-1.The article discusses the carbon depositing processes in coarse woody debris (CWD) of Ukrainian oak forests. Debris of oak stands, CWD in particular, is studied weakly in Ukraine, despite the fact that it could be large and long-term sink of sequestrated carbon. Thus, CWD needs assessment of its potential values and deposited carbon within. There for this study was used databases of Production Association "Ukrderzhlisproekt" with information about 23 thousands inventory areas where snags and logs were found in oak stands. For amounts of carbon sink calculating we used analytic information about base wood density and IPCC recommendation guidelines. Data array was distributed according to administrative units, site indexes and types of forest conditions. Average share of snags and logs volumes to trunks-in-bark volume (for areas where these kinds of CWD were found) is evaluated about 6.1 % and 5.4 %, respectively. Carbon density per unit of area is estimated on level 0.27 kg C·m-2 for snags and 0.24 kg C·m-2 for logs. There was found that carbon density per unit of area for snags increases in wetter growth conditions and carbon density for logs increases in areas with worse site index. In general, snags and logs of Ukrainian oak stands deposit 830 Gg С and 227 Gg С, respectively, which in sum is about only 0.8 % of total potential biomass carbon sink in all oak Ukrainian forests. The results indicate the insignificant role of coarse woody debris in carbon depositing processes in Ukrainian oak forests in comparison with the oak stands in Austria, in particular, where coarse dead biomass deposits about 39 % of these stands biomass carbon. Therefore, CWD values in oak forests of Ukraine are potentially larger because snags and logs during the forest inventory processes were considered only in inventory areas where its volume had been more than 5 cubic meters per ha. Accordingly, we have to hold systematic research for more accurate snags and logs volume and deposited carbon amounts within calculations and need more perfect forest inventory system for further estimation of total carbon sink in Ukrainian oak forests

The Return of Nature to the Chernobyl Exclusion Zone: Increases in Forest Cover of 1.5 Times since the 1986 Disaster

For 34 years since the 1986 nuclear disaster, the Chernobyl Exclusion Zone (ChEZ) landscapes have been protected with very limited human interventions. Natural afforestation has largely occurred throughout the abandoned farmlands, while natural disturbance regimes, which dominantly include wildfires, have become more frequent and severe in the last years. Here, we utilize the dense time series of Landsat satellite imagery (1986–2020) processed by using the temporal segmentation algorithm LandTrendr in order to derive a robust land cover and forest mask product for the ChEZ. Additionally, we carried out an analysis of land cover transitions on the former farmlands. The Random Forest classification model developed here has achieved overall accuracies of 80% (using training data for 2017) and 89% on a binary “forest/non-forest” validation (using data from 1988). The total forest cover area within the ChEZ has increased from 41% (in 1986) to 59% (in 2020). This forest gain can be explained by the afforestation that has occurred in abandoned farmlands, which compensates for forest cover losses due to large fire events in 1992, 2015–2016, and 2020. Most transitions from open landscapes to dense forest cover occurred after the year 2000 and are possibly linked to past forest management practices. We conclude that a consistent forest strategy, with the aid of remote monitoring, is required to efficiently manage new forests in the ChEZ in order to retain their ecosystem functions and to ensure sustainable habitats

Wall-to-wall mapping of carbon loss within the Chornobyl Exclusion Zone after the 2020 catastrophic wildfire

Key message We propose a framework to derive the direct loss of aboveground carbon stocks after the 2020 wildfire in forests of the Chornobyl Exclusion Zone using optical and radar Sentinel satellite data. Carbon stocks were adequately predicted using stand-wise inventory data and local combustion factors where new field observations are impossible. Both the standalone Sentinel-1 backscatter delta (before and after fire) indicator and radar-based change model reliably predicted the associated carbon loss. Context The Chornobyl Exclusion Zone (CEZ) is a mosaic forest landscape undergoing dynamic natural disturbances. Local forests are mostly planted and have low ecosystem resilience against the negative impact of global climate and land use change. Carbon stock fluxes after wildfires in the area have not yet been quantified. However, the assessment of this and other ecosystem service flows is crucial in contaminated (both radioactively and by unexploded ordnance) landscapes of the CEZ. Aims The aim of this study was to estimate carbon stock losses resulting from the catastrophic 2020 fires in the CEZ using satellite data, as field visitations or aerial surveys are impossible due to the ongoing war. Methods The aboveground carbon stock was predicted in a wall-to-wall manner using random forest modelling based on Sentinel data (both optical and synthetic aperture radar or SAR). We modelled the carbon stock loss using the change in Sentinel-1 backscatter before and after the fire events and local combustion factors. Results Random forest models performed well (root-mean-square error (RMSE) of 22.6 MgC·ha−1 or 37% of the mean) to predict the pre-fire carbon stock. The modelled carbon loss was estimated to be 156.3 Gg C (9.8% of the carbon stock in burned forests or 1.5% at the CEZ level). The standalone SAR backscatter delta showed a higher RMSE than the modelled estimate but better systematic agreement (0.90 vs. 0.73). Scots pine (Pinus sylvestris L.)-dominated stands contributed the most to carbon stock loss, with 74% of forests burned in 2020. Conclusion The change in SAR backscatter before and after a fire event can be used as a rough proxy indicator of aboveground carbon stock loss for timely carbon map updating. The model using SAR backscatter change and backscatter values prior to wildfire is able to reliably estimate carbon emissions when on-ground monitoring is impossible

⁹⁰Sr Content in the Stemwood of Forests Within Ukrainian Polissya

The consequences of the Chernobyl disaster continue to threaten humans and ecosystems across fallout gradient in Northern Ukraine and nearby. Forest ecosystems contain substantial stocks of long-lived radionuclide 90Sr which was leached from the fuel matrix during the disaster. Nowadays, there is a lack of information about current transfer factors (TF) of this radionuclide from soil to the stemwood of native tree species. We have estimated 90Sr content in the forest stemwood of three tree species utilizing models of their growth and yield and collected woody samplings. TFs provided here vary greatly across studied tree species (18.0 × 2.1±1, 8.7 × 2.8±1, and 10.4 × 6.0±1 n×10−3 m2·kg−1 (geometrical mean (GM) ± geometrical standard deviation, GSD) for the above species, respectively) and together with indicators of soil contamination allow us to reliably assess local stocks in the stemwood. Silver birch stands are estimated to deposit the highest 90Sr stocks. Herewith, at 25 years old Black alder stands could accumulate higher stocks (up to 35 MBq·ha−1) under rich growth conditions. TFs obtained in this study substantially exceed values provided by the International Atomic Energy Agency for studied tree species and thus could entail respective restrictions on use of firewood across large areas in Ukrainian Polissya. Data provided here may be harnessed to support decisions of respective stakeholders to provide credibly safe management of the contaminated forest ecosystems

War drives forest fire risks and highlights the need for more ecologically-sound forest management in post-war Ukraine

Since 24 February 2022, Ukraine has experienced full-scale military aggression initiated by the Russian Federation. The war has had a major negative impact on vegetation cover of war-affected regions. We explored interactions between pre-war forest management and the impacts of military activities in three of the most forested Ukrainian areas of interest (AOI), affected by the war. These were forests lying between Kharkiv and Luhansk cities (AOI 'East'), forests along the Dnipro River delta (AOI 'Kherson'), and those of the Chornobyl Exclusion Zone (AOI CEZ). We used Sentinel satellite imagery to create damaged forest cover masks for the year 2022. We mapped forests with elevated fire hazard, which was defined as a degree of exposure to the fire-supporting land use (mostly an agricultural land, a common source of ignitions in Ukraine). We evaluated the forest disturbance rate in 2022, as compared to pre-war rates. We documented significant increases in non-stand replacing disturbances (low severity fires and non-fire disturbances) for all three of the AOIs. Damaged forest cover varied among the AOIs (24,180 ± 4,715 ha, or 9.3% ± 1.8% in the 'East' AOI; 7,293 ± 1,925 ha, or 15.7% ± 4.1% in the 'Kherson' AOI; 7,116 ± 1,274 ha, or 5.0% ± 0.9% in the CEZ AOI). Among the forests damaged in 2022, the 'Kherson' AOI will likely have the highest proportion of an area with elevated fire hazard in the coming decades, as compared to other regions (89% vs. 70% in the 'East' and CEZ AOIs respectively). Future fire risks and extensive war-related disturbance of forest cover call for forest management to develop strategies explicitly addressing these factors

Impact of Disturbances on the Carbon Cycle of Forest Ecosystems in Ukrainian Polissya

Climate change continues to threaten forests and their ecosystem services while substantially altering natural disturbance regimes. Land cover changes and consequent management entail discrepancies in carbon sequestration provided by forest ecosystems and its accounting. Currently there is a lack of sufficient and harmonized data for Ukraine that can be used for the robust and spatially explicit assessment of forest provisioning and regulation of ecosystem services. In the frame of this research, we established an experimental polygon (area 45 km2) in Northern Ukraine aiming at estimating main forest carbon stocks and fluxes and determining the impact caused by natural disturbances and harvest for the study period of 2010–2015. Coupled field inventory and remote sensing data (RapidEye image for 2010 and SPOT 6 image for 2015) were used. Land cover classification and estimation of biomass and carbon pools were carried out using Random Forest and k-Nearest Neighbors (k-NN) method, respectively. Remote sensing data indicates a ca. 16% increase of carbon stock, while ground-based computations have shown only a ca. 1% increase. Net carbon fluxes for the study period are relatively even: 5.4 Gg C·year−1 and 5.6 Gg C C·year−1 for field and remote sensing data, respectively. Stand-replacing wildfires, as well as insect outbreaks and wind damage followed by salvage logging, and timber harvest have caused 21% of carbon emissions among all C sources within the experimental polygon during the study period. Hence, remote sensing data and non-parametric methods coupled with field data can serve as reliable tools for the precise estimation of forest carbon cycles on a regional spatial scale. However, featured land cover changes lead to unexpected biases in consistent assessment of forest biophysical parameters, while current management practices neglect natural forest dynamics and amplify negative impact of disturbances on ecosystem services

Working code and data for a wall-to-wall mapping of carbon loss within the Chornobyl Exclusion Zone after the 2020 catastrophic wildfire

Links to data in this code are from GitHub repository. But can be replaced by the files supplied here. Only code to generate models and to create figures for their validation is provided. Also code to create GMFR function (from Riemann et al. 2010 and adapted in Henderson et al. 2019) is provided. Code to: calculate C stock for training and validation data set per biomass compartment; prepare raster data (mostly in Google Earth Engine); make raster predictions; calculate C loss according to local combustion factors and NBR severity levels is available upon request. MetaData.xlsx contains a description of all files within this package, and variable explanation for provided data sets

The Forest Observation System, building a global reference dataset for remote sensing of forest biomass [data paper]

Forest biomass is an essential indicator for monitoring the Earth's ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world's forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS- based biomass products while developing new synergies between the RS and ground-based ecosystem research communities

A global reference dataset for remote sensing of forest biomass. The Forest Observation System approach

Forest biomass is an essential indicator for monitoring the Earth’s ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25ha scale from field measurements made in permanent research plots across the world's forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities. Live, most up-to-date dataset is available at https://forest-observation-system.net

The Forest Observation System, building a global reference dataset for remote sensing of forest biomass

Forest biomass is an essential indicator for monitoring the Earth's ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world's forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS- based biomass products while developing new synergies between the RS and ground-based ecosystem research communities.</p