Sapwood biomass carbon in northern boreal and temperate forests

Thurner, M.; Beer, C.; Crowther, T.; Falster, D.; Manzoni, S.; Prokushkin, A.; Schulze, E.-D.
2019 | Glob. Ecol. Biogeogr. | 28 (5) (640-660)

Aim
Information on the amount of carbon stored in the living tissue of tree stems (sapwood) is crucial for carbon and water cycle applications. Here, we aim to investigate sapwood‐to‐stem proportions and differences therein between tree genera and derive a sapwood biomass map.

Location
Northern Hemisphere boreal and temperate forests.

Time period
2010.

Major taxa studied
Twenty‐five common tree genera.

Methods
First, we develop a theoretical framework to estimate sapwood biomass for a given stem biomass by applying relationships between sapwood cross‐sectional area (CSA) and stem CSA and between stem CSA and stem biomass. These measurements are extracted from a biomass and allometry database (BAAD), an extensive literature review and our own studies. The established allometric relationships are applied to a remote sensing‐based stem biomass product in order to derive a spatially continuous sapwood biomass map. The application of new products on the distribution of stand density and tree genera facilitates the synergy of satellite and forest inventory data.

Results
Sapwood‐to‐stem CSA relationships can be modelled with moderate to very high modelling efficiency for different genera. The total estimated sapwood biomass equals 12.87 ± 6.56 petagrams of carbon (PgC) in boreal (mean carbon density: 1.13 ± 0.58 kgC m−2) and 15.80 ± 9.10 PgC in temperate (2.03 ± 1.17 kgC m−2) forests. Spatial patterns of sapwood‐to‐stem biomass proportions are crucially driven by the distribution of genera (spanning from 20–30% in Larix to > 70% in Pinus and Betula forests).

Main conclusions
The presented sapwood biomass map will be the basis for large‐scale estimates of plant respiration and transpiration. The enormous spatial differences in sapwood biomass proportions reveal the need to consider the functionally more important sapwood instead of the entire stem biomass in global carbon and water cycle studies. Alterations in tree species distribution, induced by forest management or climate change, can strongly affect the available sapwood biomass even if stem biomass remains unchanged.

Reviews and syntheses: Carbon use efficiency from organisms to ecosystems – definitions, theories, and empirical evidence

Manzoni, S.; Capek, P., Porada, P.; Thurner, M.; Winterdahl, M.; Beer, C.; Brüchert, V.; Frouz, J.; Hermann, A.M.; Lindahl, B.D.; Lyon, S.W.; Santruckova, H.; Vico, G.; Way, D.
2018 | Biogeosciences | 15 (5929-5949)

The cycling of carbon (C) between the Earth surface and the atmosphere is controlled by biological and abiotic processes that regulate C storage in biogeochemical compartments and release to the atmosphere. This partitioning is quantified using various forms of C-use efficiency (CUE) – the ratio of C remaining in a system to C entering that system. Biological CUE is the fraction of C taken up allocated to biosynthesis. In soils and sediments, C storage depends also on abiotic processes, so the term C-storage efficiency (CSE) can be used. Here we first review and reconcile CUE and CSE definitions proposed for autotrophic and heterotrophic organisms and communities, food webs, whole ecosystems and watersheds, and soils and sediments using a common mathematical framework. Second, we identify general CUE patterns; for example, the actual CUE increases with improving growth conditions, and apparent CUE decreases with increasing turnover. We then synthesize >5000CUE estimates showing that CUE decreases with increasing biological and ecological organization – from unicellular to multicellular organisms and from individuals to ecosystems. We conclude that CUE is an emergent property of coupled biological–abiotic systems, and it should be regarded as a flexible and scale-dependent index of the capacity of a given system to effectively retain C.

Uncertainty quantification of extratropical forest biomass in CMIP5 models over the Northern Hemisphere

Yang, C.-E.; Mao, J.; Hoffman, F.M.; Ricciuto, D.M.; Fu, J.S.; Jones, C.D.; Thurner, M.
2018 | Sci Rep | 8 (10962)

Simplified representations of processes influencing forest biomass in Earth system models (ESMs) contribute to large uncertainty in projections. We evaluate forest biomass from eight ESMs outputs archived in the Coupled Model Intercomparison Project Phase 5 (CMIP5) using the biomass data synthesized from radar remote sensing and ground-based observations across northern extratropical latitudes. ESMs exhibit large biases in the forest distribution, forest fraction, and mass of carbon pools that contribute to uncertainty in forest total biomass (biases range from −20 Pg C to 135 Pg C). Forest total biomass is primarily positively correlated with precipitation variations, with surface temperature becoming equally important at higher latitudes, in both simulations and observations. Relatively small differences in forest biomass between the pre-industrial period and the contemporary period indicate uncertainties in forest biomass were introduced in the pre-industrial model equilibration (spin-up), suggesting parametric or structural model differences are a larger source of uncertainty than differences in transient responses. Our findings emphasize the importance of improved (1) models of carbon allocation to biomass compartments, (2) distribution of vegetation types in models, and (3) reproduction of pre-industrial vegetation conditions, in order to reduce the uncertainty in forest biomass simulated by ESMs.

Unexpectedly large impact of forest management and grazing on global vegetation biomass

Erb, K.-H.; Kastner, T.; Plutzar, C.; Bais, A.L.S.; Carvalhais, N.; Fetzel, T.; Gingrich, S.; Haberl, H.; Lauk, C.; Niedertscheider, M.; Pongratz, J.; Thurner, M.; Luyssaert, S.
2018 | Nature | 553 (73-76)

Carbon stocks in vegetation have a key role in the climate system1,2,3,4. However, the magnitude, patterns and uncertainties of carbon stocks and the effect of land use on the stocks remain poorly quantified. Here we show, using state-of-the-art datasets, that vegetation currently stores around 450 petagrams of carbon. In the hypothetical absence of land use, potential vegetation would store around 916 petagrams of carbon, under current climate conditions. This difference highlights the massive effect of land use on biomass stocks. Deforestation and other land-cover changes are responsible for 53–58% of the difference between current and potential biomass stocks. Land management effects (the biomass stock changes induced by land use within the same land cover) contribute 42–47%, but have been underestimated in the literature. Therefore, avoiding deforestation is necessary but not sufficient for mitigation of climate change. Our results imply that trade-offs exist between conserving carbon stocks on managed land and raising the contribution of biomass to raw material and energy supply for the mitigation of climate change. Efforts to raise biomass stocks are currently verifiable only in temperate forests, where their potential is limited. By contrast, large uncertainties hinder verification in the tropical forest, where the largest potential is located, pointing to challenges for the upcoming stocktaking exercises under the Paris agreement.

Land-use and land-cover change carbon emissions between 1901 and 2012 constrained by biomass observations

Li, W.; Ciais, P.; Peng, S.; Yue, C.; Wang, Y.; Thurner, M.; Saatchi, S. S.; Arneth, A.; Avitabile, V.; Carvalhais, N.; Harper, A. B.; Kato, E.; Koven, C.; Liu, Y. Y.; Nabel, J. E. M. S.; Pan, Y.; Pongratz, J.; Poulter, B.; Pugh, T. A. M.; Santoro, M.; Sitch, S.; Stocker, B. D.; Viovy, N.; Wiltshire, A.; Yousefpour, R.; Zaehle, S.
2017 | Biogeosciences | 14 (5053-5067)

The use of dynamic global vegetation models (DGVMs) to estimate CO2 emissions from land-use and land-cover change (LULCC) offers a new window to account for spatial and temporal details of emissions and for ecosystem processes affected by LULCC. One drawback of LULCC emissions from DGVMs, however, is lack of observation constraint. Here, we propose a new method of using satellite- and inventory-based biomass observations to constrain historical cumulative LULCC emissions (ELUCc) from an ensemble of nine DGVMs based on emerging relationships between simulated vegetation biomass and ELUCc. This method is applicable on the global and regional scale. The original DGVM estimates of ELUCc range from 94 to 273 PgC during 1901–2012. After constraining by current biomass observations, we derive a best estimate of 155 ± 50 PgC (1σ Gaussian error). The constrained LULCC emissions are higher than prior DGVM values in tropical regions but significantly lower in North America. Our emergent constraint approach independently verifies the median model estimate by biomass observations, giving support to the use of this estimate in carbon budget assessments. The uncertainty in the constrained ELUCc is still relatively large because of the uncertainty in the biomass observations, and thus reduced uncertainty in addition to increased accuracy in biomass observations in the future will help improve the constraint. This constraint method can also be applied to evaluate the impact of land-based mitigation activities.

Evaluation of climate-related carbon turnover processes in global vegetation models for boreal and temperate forests

Thurner, M.; Beer, C.; Ciais, P.; Friend, A. D.; Ito, A.; Kleidon, A.; Lomas, M. R.; Quegan, S.; Rademacher, T. T.; Schaphoff, S.; Tum, M.; Wiltshire, A.; Carvalhais, N.
2017 | Glob. Change Biol. | 23 (8) (3076-3091)

Turnover concepts in state-of-the-art global vegetation models (GVMs) account for various processes, but are often highly simplified and may not include an adequate representation of the dominant processes that shape vegetation carbon turnover rates in real forest ecosystems at a large spatial scale. Here we evaluate vegetation carbon turnover processes in GVMs participating in the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP; including HYBRID4, JeDi, JULES, LPJml, ORCHIDEE, SDGVM, and VISIT) using estimates of vegetation carbon turnover rate (k) derived from a combination of remote sensing based products of biomass and net primary production (NPP). We find that current model limitations lead to considerable biases in the simulated biomass and in k (severe underestimations by all models except JeDi and VISIT compared to observation-based average k), likely contributing to underestimation of positive feedbacks of the northern forest carbon balance to climate change caused by changes in forest mortality. A need for improved turnover concepts related to frost damage, drought and insect outbreaks in order to better reproduce observation-based spatial patterns in k is identified. Since direct frost damage effects on mortality are usually not accounted for in these GVMs, simulated relationships between k and winter length in boreal forests are not consistent between different regions and strongly biased compared to the observation-based relationships. Some models show a response of k to drought in temperate forests as a result of impacts of water availability on NPP, growth efficiency or carbon balance dependent mortality as well as soil or litter moisture effects on leaf turnover or fire. However, further direct drought effects like carbon starvation (only in HYBRID4) or hydraulic failure are usually not taken into account by the investigated GVMs. While they are considered dominant large-scale mortality agents, mortality mechanisms related to insects and pathogens are not explicitly treated in these models.

Large-scale variation in boreal and temperate forest carbon turnover rate related to climate

Thurner, M.; Beer, C.; Carvalhais, N.; Forkel, M.; Santoro, M.; Tum, M.; Schmullius, C.
2016 | Geophys Res Lett | 43 (4576-4585)

Forest growing stock volume of the northern hemisphere: an estimate for 2010 derived from Envisat ASAR data

Santoro, M.; Beaudoin, A.; Beer, C.; Cartus, O.; Fransson, J. E. S.; Hall, R.; Pathe, C.; Schmullius, C.; Shvidenko, A.; Schepaschenko, D.; Thurner, M.; Wegmüller, U.
2015 | Remote Sens. Environ. | 168 (316-334)

Carbon stock and density of northern boreal and temperate forests

Thurner, M.; Beer, C.; Santoro, M.; Carvalhais, N.; Wutzler, T.; Schepaschenko, D.; Shvidenko, A.; Kompter, E.; Ahrens, B.; Levick, S. R.; Schmullius, C.
2014 | Glob. Ecol. Biogeogr. | 23 (297-310)

Global covariation of carbon turnover times with climate in terrestrial ecosystems

Carvalhais, N.; Forkel, M.; Khomik, M.; Bellarby, J.; Jung, M.; Migliavacca, M.; Mu, M.; Saatchi, S.; Santoro, M.; Thurner, M.; Weber, U.; Ahrens, B.; Beer, C.; Cescatti, A.; Randerson, J.T.; Reichstein, M.
2014 | Nature | 514 (213-217)

Extraction of Plant Physiological Status from Hyperspectral Signatures Using Machine Learning Methods

Doktor, D; Lausch, A; Spengler, D; Thurner, M
2014 | Remote Sens. | 6 (12) (12247-12274)
algorithms , chlorophyll content , classification , crop , feature reduction , hyperspectral data , land-cover , model , prosail , random forest , random forests , regression , vegetation , vegetation status , water-stress

Identifying environmental controls on vegetation greenness phenology through model-data integration

Forkel, M; Carvalhais, N; Schaphoff, S; von Bloh, W; Migliavacca, M; Thurner, M; Thonicke, K
2014 | Biogeosciences | 11 (23) (7025-7050)
climate change , earth system models , eddy-covariance data , gross primary production , growing-season , in situ measurements , land-surface models , leaf-area index , ndvi time-series , terrestrial ecosystems

Contact information

Visiting addresses:

Geovetenskapens Hus,
Svante Arrhenius väg 8, Stockholm

Arrheniuslaboratoriet, Svante Arrhenius väg 16, Stockholm (Unit for Analytical and Toxicological Chemistry)

Mailing address:
Department of Environmental Science and Analytical Chemistry (ACES)
Stockholm University
106 91 Stockholm

Press enquiries should be directed to:

Stella Papadopoulou
Science Communicator
Phone +46 (0)8 674 70 11
stella.papadopoulou@aces.su.se