This study examined the carbon (C) concentration of the major tree species (Scots pine, Norway spruce, and Birch) in Sweden based on destructively sampled biomass data. The examination was made using single trees and comprised three components: branches with needles, stemwood with bark, and stump with roots. We developed a weighted C concentration estimator accounting for fresh weights of tree components to infer the C concentration at the population level. Significant differences in C concentration (%) were found among species, with the highest in pine (50.671 +/- 0.211), followed by spruce (49.518 +/- 0.164) and the lowest in birch (49.347 +/- 0.241). Additionally, the C concentration varied among tree components, regardless of tree size, growth rate, and site conditions. At the national level, we applied the estimated species- and component-specific C concentration constants to the measured total biomass of the major tree species from the National Forest Inventory. This extrapolation revealed that the average C concentration of major trees across all forestlands in Sweden was approximately 50.012%. These findings have significant implications for accurate C sequestration reporting in the LULUCF sector.

Our research targets the role of forests under the international Paris Climate Agreement, the EU Green Deal and Forest Strategy. In line with the latter objectives, Member States are expected to encourage forest owners to contribute to international climate goals via national strategic plans and new management measures. How forest owners will respond, however, to a range of climate smart forestry (CSF) measures in the near future, is not well known. After postal and email distribution in 2020, 98 Swedish (response rate 21

Changes over time in annual basal area growth and mean height for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) over the period, 1983-2020 were studied using sample tree data from temporary plots recorded in the Swedish National Forest Inventory. The annual basal area growth was derived from the last measured full ring on increment cores. Using 20 to 60-year-old dominant trees, the mean height and annual basal area growth were examined as functions of tree, stand and site conditions, and trends were assessed mainly using residual analyses over time. A significant increase in mean height at a given age was found for both species, but the annual basal area growth level remained stable over the 38-year period. Currently, at a given age of 50 annual rings at breast height, the mean heights of pines and spruces increased on average by 10.1% (i.e. similar to 2 m), compared to 50 year-old pines and spruces in the 1980s, and the increase was similar in the different regions. The results suggest that trees have become taller and slenderer in Swedish forests. Increasing tree height over time at a given age in Northern Europe has been documented in several reports and many causes have been suggested, such as changed forest management, increasing temperatures and nitrogen deposition. We suggest that elevated CO2 in the air and improved water-use efficiency for the trees might also be strong drivers.

Background Under the growing pressure to implement mitigation actions, the focus of forest management is shifting from a traditional resource centric view to incorporate more forest ecosystem services objectives such as carbon sequestration. Estimating the above-ground biomass in forests using airborne laser scanning (ALS) is now an operational practice in Northern Europe and is being adopted in many parts of the world. In the boreal forests, however, most of the carbon (85%) is stored in the soil organic (SO) matter. While this very important carbon pool is “invisible” to ALS, it is closely connected and feeds from the growing forest stocks. We propose an integrated methodology to estimate the changes in forest carbon pools at the level of forest stands by combining field measurements and ALS data. Results ALS-based models of dominant height, mean diameter, and biomass were fitted using the field observations and were used to predict mean tree biophysical properties across the entire study area (50 km 2 ) which was in turn used to estimate the biomass carbon stocks and the litter production that feeds into the soil. For the soil carbon pool estimation, we used the Yasso15 model. The methodology was based on (1) approximating the initial soil carbon stocks using simulations; (2) predicting the annual litter input based on the predicted growing stocks in each cell; (3) predicting the soil carbon dynamics of the annual litter using the Yasso15 soil carbon model. The estimated total carbon change (standard errors in parenthesis) for the entire area was 0.741 (0.14) Mg ha −1 yr −1 . The biomass carbon change was 0.405 (0.13) Mg ha −1 yr −1 , the litter carbon change (e.g., deadwood and leaves) was 0.346 (0.027) Mg ha −1 yr −1 , and the change in SO carbon was − 0.01 (0.003) Mg ha −1 yr −1 . Conclusions Our results show that ALS data can be used indirectly through a chain of models to estimate soil carbon changes in addition to changes in biomass at the primary level of forest management, namely the forest stands. Having control of the errors contributed by each model, the stand-level uncertainty can be estimated under a model-based inferential approach.

The carbon ecosystem service is important due to climate change and the effects of forest management practices. Many research efforts have been made to relate carbon storage with forest management practices and identify the most suitable sites for this purpose. Different methods for digitizing and mapping of carbon ecosystem services are needed to improve the value of ecosystem services at the local scale and to decide on natural resource management. In this study, a decision-making model to guide carbon storage and sequestration mapping has been established from ecosystem services and tested with real data. One objective of this study is to provide a carbon suitability map for stands of high carbon storage/growth potential. A second goal is to develop a template guiding surveyors to identify and map areas with different carbon storage potential. Stands of high carbon storage/growth potential were mapped and identified as the carbon suitability hotspots in Turkey at the local scale, taking into account the methods used in previous modeling and mapping studies. Criteria for carbon suitability mapping for Belgrad Forest were determined by using expert opinions and literature. Finally, carbon storage and carbon sequestration values were calculated. The model presented will reduce the uncertainty associated with carbon suitability mapping. The work presented suggests that local studies are needed to improve carbon mapping. The Multi-Criteria Decision Analysis (MCDA) methods and expert knowledge in forest studies can be utilized to assess their stands suitable for carbon storage. Based on these stands, zones suitable for carbon storage can be developed.

Key message Using satellite-based maps, Ceccherini et al. (Nature 583:72-77, 2020) report abruptly increasing harvested area estimates in several EU countries beginning in 2015. Using more than 120,000 National Forest Inventory observations to analyze the satellite-based map, we show that it is not harvested area but the map’s ability to detect harvested areas that abruptly increases after 2015 in Finland and Sweden.

Reversing the European trend toward a declining land carbon sink has become the new mantra. The decision to increase net carbon uptake in the forest, however, is made without adequately considering the consequences for the circular bioeconomy and climate change mitigation more generally. LULUCF (Land Use, Land Use Change and Forestry) accounting fails to balance net carbon uptake with the positive substitution effects from forest use recorded in the energy sector. The singular focus on the net forest carbon sink distracts attention from the fact that, over the past century, many EU Member states have managed to harvest ever larger amounts of forest, and, simultaneously, to continuously increase both forest carbon stocks, as well as the size of the annual forest increment. In the language of the European Commission’s proposed LULUCF policy framework, however, high harvesting rates and high forest use intensity are seen as anathema to climate change mitigation because they are thought to threaten the reliability of the EU UNFCCC emission reduction commitment framework, as well as the longevity of Europe’s forests, more generally. This, at least, is the unabashed message of one recent Joint Research Centre (JRC) assessment of EU forestry, which argues that rapid increases in harvest rates challenge the environmental integrity of EU emission-reduction commitments. According to the authors, ‘the loss of carbon in standing forests will require additional efforts in other sectors to reach the EU climate neutrality target by 2050’.1 We explore the parameters of this assessment, highlighting the fact that preferences for more protected forests obscure our understanding of the climate benefits forestry and forest resource use can provide. We argue the continuous net annual contributions to the global carbon budget provided by the circular bioeconomy (avoided emissions, net removals and renewed forest growth) should be more carefully considered. Increasing net forest carbon uptake by reducing forest use intensity (i.e., annual harvest) is not the only, nor is it even the most beneficial, pathway to increasing LULUCF-based climate change mitigation potential. Policymakers should pay greater attention both to the mix of micro-level mechanisms and incentives created by the EU LULUCF policy framework and the mix of public and private sector interests and investment goals intended to undergird future forest growth and LULUCF-based mitigation potential. As we demonstrate, promoting reforestation efforts beyond Managed Forest Lands (MFL) has contributed only minimally to the global carbon budget and has failed to garner the kind of investment momentum required to make it a meaningful mitigation solution. MFL, on the other hand, have witnessed far greater contributions to the global carbon budget but are generally not fully mobilized in the EU climate policy framework. Striking an appropriate balance between the many climate change mitigation, human livelihood and consumption benefits forests and forest-based resources can provide, on the one hand, and protected, biodiverse-rich forest environments, on the other, requires a more balanced approach.

We analyse the short- and long-term consequences for atmospheric greenhouse gas (GHG) concentrations of forest management strategies and forest product uses in Sweden by comparing the modelled consequences of forest resource use vs. increased conservation at different levels of GHG savings from carbon sequestration and product substitution with bioenergy and other forest products. Increased forest set-asides for conservation resulted in larger GHG reductions only in the short term and only when substitution effects were low. In all other cases, forest use was more beneficial. In all scenarios, annual carbon dioxide (CO2) sequestration rates declined in conservation forests as they mature, eventually approaching a steady state. Forest set-asides are thus associated with increasing opportunity costs corresponding to foregone wood production and associated mitigation losses. Substitution and sequestration rates under all other forest management strategies rise, providing support for sustained harvest and cumulative mitigation gains. The impact of increased fertilization was everywhere beneficial to the climate and surpassed the mitigation potential of the other scenarios. Climate change can have large-positive or negative-influence on outcomes. Despite uncertainties, the results indicate potentially large benefits from forest use for wood production. These benefits, however, are not clearly linked with forestry in UNFCCC reporting, and the European Union's Land Use, Land-Use Change and Forestry carbon accounting, framework may even prevent their full realization. These reporting and accounting frameworks may further have the consequence of encouraging land set-asides and reduced forest use at the expense of future biomass production. Further, carbon leakage and resulting biodiversity impacts due to increased use of more GHG-intensive products, including imported products associated with deforestation and land degradation, are inadequately assessed. Considerable opportunity to better mobilize the climate change mitigation potential of Swedish forests therefore remains.

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.

Bade KP och EU:s nya forordning (EU/2018/841) sarredovisar och bokfor avskogning som en egen aktivitet. Sveriges klimatrapportering under Klimatkonventionen, KP och EU anvander data om arealer for ...

15 Long-standing debate over the benefits of forest conservation vs. those of forest resource use and 16 substitution continue to occupy attention in Europe and beyond. To study this question, we 17 simulate the short- and long-term consequences for atmospheric greenhouse gas (GHG) 18 concentrations of different forest management strategies and forest product uses in Sweden. We compare the projected short- and long-term consequences of increasing forest use vs. increasing 20 land set-asides. In all scenarios but one, forest management for wood production results in higher 21 net GHG reduction than the alternative to set-aside forests for conservation. In all scenarios, 22 annual carbon dioxide (CO 2 ) sequestration rates in conservation forests decline as maturing 23 forests eventually reach a steady state, while they rise in all other forest management strategies. Thus, there is an apparent tradeoff between wood production and nature conservation. Forest set- 25 asides are associated with sizable long-term opportunity costs corresponding to the foregone 26 wood production capacity. Retained in the circular bioeconomy system over the long-term, forest 27 management for wood production eventually stabilizes at significantly higher amounts than a 28 management system which promotes greater shares of forest protection and conservation. In all 29 cases, the long-term mitigation gains from wood production are cumulative and significant. 30 Likewise, the indicative level of wood supply for biobased production that can be maintained 31 without causing systematic loss in land carbon stocks is large. Such long-term consequences, 32 however, are not properly accounted for in the European Union’s (EU’s) legislative LULUCF 33 (Land Use, Land-Use Change and Forestry) carbon accounting framework, which effectively 34 encourages land set-asides at the expense of forest wood production capacity. 35

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).

Genom att aktiviteter inom markanvandning och skogsbruk (LULUCF-sektorn) fatt storre betydelse i klimatarbetet, saval internationellt (EU/2018/841) som nationellt (SOU 2020:4) har behovet av forbattrad uppfoljning av dessa aktiviteter aktualiserats. Det finns aven ett behov av att forbattra bedomningen av potentialen, dvs. effekten pa vaxthusgasbalansen av att atgarderna infors. I denna rapport analyseras hur kolinlagringen kan oka genom beskogning av jordbruksmark och hur atgarden kan foljas upp. I uppdraget ingar att (i) foresla hur forandrade utslapp och upptag kan kvantifieras pa objektsniva i samband med utford atgard, (ii) identifiera tillgangliga datakallor for att folja upp atgarderna, (iii) foresla eventuellt ytterligare behov av data for uppfoljning av atgarderna. Eftersom omfattande inventering kravs for mata effekten av beskogning pa plats har vi tagit fram en uppsattning typbestand for olika tradslag (gran, tall, bjork, asp, contortatall, ek, lark, bok), bordighet (lag, medel, hog), tidigare markanvandning (vallbruk, odling av ettariga grodor respektive grontrada) for tre regioner (Gotaland, Svealand, Norrland), dvs. 216 olika alternativ. Dessutom har vi ocksa tagit fram motsvarande uppsattning for fall dar foryngringen ar nagot mindre lyckad. De olika typbestanden simulerades med Heureka Planwise med komplettering av markkolsdata for tidigare markanvandning som simulerades med ICBM-modellen. For att ocksa visa effekten av att valja snabbvaxande tradslag som poppel och hybridasp gjordes en litteraturgenomgang som jamfordes med de simulerade bestanden. Det ar stor skillnad i utfallet for de olika simulerade beskogningsalternativen. Gran binder i genomsnitt 2,3 ton C ha-1 ar-1 over en omloppstid, medan bjork binder 0,9 ton C ha-1 ar-1 over en omloppstid. Generellt sker ett storre kolupptag vid lyckade foryngringar med i snitt 1,4 ton C ha-1 ar-1 nettoupptag over en omloppstid vid 2000 stammar vid en atervaxtinventering jamfort med 1,1 ton C ha-1 ar-1 vid 1000 stammar. Hogre bonitet ger i snitt 1,7 ton C ha-1 ar-1 jamfort med 0,9 ton C ha-1 ar-1 vid lagre bonitet i genomsnitt over samtliga simulerade bestand. En intressant observation ar att det tar ett antal ar innan bestanden bidrar som nettosanka (men med stor variation givet variationerna ovan). Detta beror pa att nedbrytningen av det gamla kolet i marken inledningsvis ar hogre an tillforseln av nytt kol. Aven om man ska tolka dessa simulerade resultat med viss forsiktighet visar det att tidigare markanvandning bor tas i beaktande for var beskogning bor ske och med vilka tradslag. Det finns annars en risk att nyttan med beskogningen begransas bade i total effekt och tidsmassigt for att bidraget ska bli signifikant relativt befintliga klimatmal. Underlagen fran de simulerade typbestanden kan anvandas i kombination med aktivitetsdata, dvs. arealer for aktiv plantering for att beraknas totaleffekt av beskogning. Genomsnitt kan t.ex. tas fram som kan komplettera de utslapps- och upptagsfaktorer som anvands i klimatrapporteringen idag i kombination med data fran SLU Riksskogstaxeringen (RT), exempel ges i rapporten pa regionvisa faktorer. Det ar ocksa mojligt att anvanda typvarden pa den aggregeringsniva som ar lamplig givet de aktivitetsdata som finns tillgangliga. Andra kallor for aktivitetsdata kan vara den anmalan som gors till Lansstyrelsen nar jordbruksmark tas ur bruk eller uppgifter om att jordbruksmarken inte langre ingar i ansokan om stod inom landsbygdsprogrammet. Om en bra uppfoljning ska kunna goras i framtiden behover ett system som sammanstaller den anmalan som gors idag och de ansokningar om stod som kan bli verklighet om aktiviteten beskogning kommer ges stod i nagon form (antingen genom ett nytt system eller genom att det implementeras i befintliga stodsystem). Uppfoljning kan goras genom stickprovsinventering i lampliga tidsintervall men ocksa genom att markagaren informerar ansvarig myndighet lopande om bestandets utveckling, i.e. i vilken utstrackning beskogningen varit lyckad (kanske vart femte ar). Uppgiftslamnarbordan ska dock hallas sa lag som mojligt for att inte minska intresset for atgarden. Nar det galler potentialen av beskogning relativt klimatmal till 2030 och 2045 ar det uppenbart att bidraget inte hinner bli sa stort till 2030 givet att det tar tid innan tillvaxten far fart och effekten av att nedbrytningen av markkol ar hogre an tillforseln av nytt kol initialt. Vi har beraknat ett antal scenarier med stod av simuleringar av typbestand. Utgangspunkten har varit dagens beskogningsintensitet och tradslagsfordelning. Den additionella effekten jamfort med det bidrag som aktiviteten beskogning ger idag, hamnar pa i storleksordningen 50 kton CO2 ar--1 10 ar efter att scenarierna startar, men efter 25 ar, dvs. runt 2045 kan bidraget bli mer an 1 000 kton CO2 ar-1 vid beskogning pa 10 kha ar-1 i 20 ar, dvs. totalt 200 kha. Det ar dock stor variation beroende pa vilken beskogningsstrategi som valjs. Ett alternativ dar andelen lov okar samtidigt som vi antar att battre lokaler valjs ger bara ett extra bidrag pa drygt 100 kton CO2 ar-1 efter 25 ar. Kortsiktigt verkar det effektivt att satsa pa att plantera snabbvaxande tradslag som poppel eller hybridasp, atminstone pa en del av den aktuella arealen. Beskogningen bidrar inte bara med inlagring av koldioxid utan ocksa till produktion av traravara. Efter 60 ar kan bidraget fran beskogad mark, dvs. den mark som beskogas i scenarierna bidra med mellan ca 0,4 miljoner m3 sk ar-1 (scenario lov) och ca 1,4 miljoner m3 sk ar-1 (scenario BAUx2) i gallring. Om utvecklingen foljer alternativ Hog kan det handla om uppemot 2 miljoner m3 sk ar-1for scenario BAUx2 (som innebar att upp till 400 kha mark tas i ansprak for beskogning). Jamfort med dagens avverkningsnivaer motsvarar detta ca 1-2% av det arliga virkesuttaget. Dartill tillkommer forstas virkesleveranser nar bestanden slutavverkas men den kolmangden ar inkluderad i nettoupptaget. Potentiellt skulle beskogning och produktion av skogsravara pa nedlagd jordbruksmark kunna frigora produktiv skogsmark for andra andamal, t.ex. for okat bevarande av biologisk mangfald. Hur vara marker utnyttjas i framtiden ar dock en svar balansgang, samtidigt som jordbruksmark laggs ner, pekar mycket pa dessa arealer kan behovas for livsmedelsproduktion i framtiden. Det ar darfor rimligt att inte inteckna alltfor stor areal for beskogning. Var bedomning ar att de 200 kha som vi anvant i denna studie inte i alltfor stor utstrackning inkraktar pa framtida livsmedelsproduktion eftersom marken i huvudsak redan tagits ur jordbruksproduktion.

The announced goal of reversing the European trend toward a declining land carbon sink has garnered much ink. Words can, however, be misleading. Annual additions/contributions (sinks) to the land carbon sink (stocks) from growing forest and increasing forest cover have slowed marginally in recent years. However, the existing European land forest sink (stocks) has (have) expanded continuously across most or all of the 20th century and on into the 21st. More importantly perhaps, EU Member states with significant long-term investments in the forestry sector have historically witnessed strong forest expansion and notmerely with the initiation of international attention to climate change mitigation through the UNFCCC negotiating and climate commitment framework. In this context, frequent assaults on forestry from multiple directions are cause for some bewilderment. We first highlight weaknesses in claims of increased forest use intensity and illustrate that forestry in the Nordic countries has a remarkably small and stable footprint over the 20th and 21st centuries. Addressing the second problem, however, understanding why such attacks occur in the first place, is more complex. Methodologically speaking, challenges to forestry should presumably be balanced by an understanding of the many human welfare benefits forests and the practice of forestry currently provide, as well as the costs of relinquishing those practices. Perhaps due to strong preferences among NGO’s and in parts of the academic community for natural, untouched, biodiverse forests, the benefits of forestry and forest resource use are consistently under-appreciated. Striking a balance between the desire for natural and biodiverse-rich forest environments on the one hand, and the climate change mitigation (and adaptation) benefits of forestry, forest resource use and substitution on the other is presumably a political and socio-economic necessity. The real question may be to what extent bias in favor of the “natural” may ultimately disrupt real, measurable progress toward effective climate change mitigation? Continuous, positive mitigation-related contributions to the growing European land cover sink (stocks), as well as to the global carbon budget (through annual net removals and substitution), have been and should remain the norm. These goals ultimately require an aggressive EU LULUCF strategy capable of fully mobilizing forest and forest resource use in favor of the goal of climate change mitigation (and adaptation).

For boreal forests in colder climates, changes in environmental conditions are hypothesised to substantially affect ecosystem processes. In this study, trends of top height growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) were analysed using permanent sample plot data from more than 300 long-term experimental sites distributed from temperate zones to the boreal forest conditions in Sweden. By regression analyses, the effects of temperature-sum and precipitation-sum on top height growth were assessed in the period 1986-2018. A significant upward temporal trend in height growth was observed for both species, with the trend more pronounced after the millennium shift. The magnitude of the annual relative height growth after the millennium was about 16.92% and 9.54% higher than expected, respectively for Scots pine and Norway spruce. A potential climate response on height growth was found for both species with temperature-sum positively correlated with top height growth. No significant effect of precipitation-sum on height growth was observed for either species. Our results suggest improved growing conditions and forest sites became more productive in response to increasing temperature in the northern temperate and boreal regions. The increasing growth trends may offer shorter rotation periods and increased forest value for Norway spruce and Scots pine, coupled with contributions of boreal forests to the emerging bio-economy and the regulation of global atmospheric carbon.

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).

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

The pipe model approach was compared with foliage biomass models by using the cross-sectional area at the tree crown base for predicting foliage biomass of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.). We evaluated the impacts of site type, fertilization, and climate on the relationship between foliage biomass and cross-sectional area at the tree crown base, referred as to the pipe model ratio. Our hypotheses were that (i) the pipe model approach is a more precise and accurate method for foliage prediction than the traditional biomass models and (ii) the pipe model ratio for foliage does not explicitly depend on any single environmental driver. Data used here consisted of felled trees from Finnish and Swedish biomass studies. These data were analyzed by linear mixed models with different covariates, and the uncertainties of different modelling approaches were evaluated. The pipe model outperformed other models for Scots pine but not for Norway spruce. Results showed larger pipe model ratios for Scots pine in herb-rich forests compared with those of trees in subxeric heath forest. Results from fertilized trees indicated that the addition of nitrogen temporarily increased foliage biomass.