Browsing by Subject "CARBON-CYCLE"

Sort by: Order: Results:

Now showing items 1-10 of 10
  • Trotsiuk, Volodymyr; Hartig, Florian; Cailleret, Maxime; Babst, Flurin; Forrester, David I.; Baltensweiler, Andri; Buchmann, Nina; Bugmann, Harald; Gessler, Arthur; Gharun, Mana; Minunno, Francesco; Rigling, Andreas; Rohner, Brigitte; Stillhard, Jonas; Thurig, Esther; Waldner, Peter; Ferretti, Marco; Eugster, Werner; Schaub, Marcus (2020)
    The response of forest productivity to climate extremes strongly depends on ambient environmental and site conditions. To better understand these relationships at a regional scale, we used nearly 800 observation years from 271 permanent long-term forest monitoring plots across Switzerland, obtained between 1980 and 2017. We assimilated these data into the 3-PG forest ecosystem model using Bayesian inference, reducing the bias of model predictions from 14% to 5% for forest stem carbon stocks and from 45% to 9% for stem carbon stock changes. We then estimated the productivity of forests dominated by Picea abies and Fagus sylvatica for the period of 1960-2018, and tested for productivity shifts in response to climate along elevational gradient and in extreme years. Simulated net primary productivity (NPP) decreased with elevation (2.86 +/- 0.006 Mg C ha(-1) year(-1) km(-1) for P. abies and 0.93 +/- 0.010 Mg C ha(-1) year(-1) km(-1) for F. sylvatica). During warm-dry extremes, simulated NPP for both species increased at higher and decreased at lower elevations, with reductions in NPP of more than 25% for up to 21% of the potential species distribution range in Switzerland. Reduced plant water availability had a stronger effect on NPP than temperature during warm-dry extremes. Importantly, cold-dry extremes had negative impacts on regional forest NPP comparable to warm-dry extremes. Overall, our calibrated model suggests that the response of forest productivity to climate extremes is more complex than simple shift toward higher elevation. Such robust estimates of NPP are key for increasing our understanding of forests ecosystems carbon dynamics under climate extremes.
  • Korrensalo, Aino; Kettunen, Laura; Laiho, Raija; Alekseychik, Pavel; Vesala, Timo; Mammarella, Ivan; Tuittila, Eeva-Stiina (2018)
    Question: Peatlands are globally important for carbon storage due to the imbalance between plant biomass production and decomposition. Distribution of both live standing biomass (BM, dry mass g/m(2)) and biomass production (BMP, dry mass gm(-2) growing season(-1)) are known to be dependent on the water table (WT). However, the relations of BM and BMP to WT variation are poorly known. Here we investigated, how the above- and below-ground BM and BMP of three different plant functional types (PFTs), dwarf shrubs, sedges and Sphagnum mosses, relate to natural WT variation within an ombrotrophic boreal bog. In addition, we estimated ecosystem-level BMP and compared that with ecosystem net primary production (NPP) derived from eddy covariance (EC) measurements. Location: Siikaneva bog, Ruovesi, Finland. Methods: We quantified above- and below-ground BM and BMP of PFTs along the WT gradient, divided into six plant community types. Plant community scale BM and BMP were up-scaled to the ecosystem level. NPP was derived from EC measurements using a literature-based ratio of heterotrophic respiration to total ecosystem respiration. Results: BM varied from 211 to 979 g/m(2) among the plant community types, decreasing gradually from dry to wet community types. In contrast, BMP was similar between plant community types (162-216 g/m(2)), except on nearly vegetation-free bare peat surfaces where it was low (38 g/m(2)). Vascular plant BM turnover rate (BMP:BM, per year) varied from 0.14 to 0.30 among the plant community types, being highest in sedge-dominated hollows. On average 56% of the vascular BM was produced below ground. Mosses, when present, produced on average 31% of the total BM, ranging from 16% to 53% depending on community type. EC-derived NPP was higher than measured BMP due to underestimation of certain components. Conclusions: We found that the diversity of PFTs decreases the spatial variability in productivity of a boreal bog ecosystem. The observed even distribution of BMP resulted from different WT optima and BMP:BM of dwarf shrubs, sedges and Sphagnum species. These differences in biomass turnover rate and species responses to environmental conditions may provide a resilience mechanism for bog ecosystems in changing conditions.
  • Navarro, J. C. Acosta; Smolander, S.; Struthers, H.; Zorita, E.; Ekman, A. M. L.; Kaplan, J. O.; Guenther, A.; Arneth, A.; Riipinen, I. (2014)
  • Gaillard, M. -J.; Sugita, S.; Mazier, F.; Trondman, A. -K.; Brostrom, A.; Hickler, T.; Kaplan, J. O.; Kjellstrom, E.; Kokfelt, U.; Kunes, P.; Lemmen, C.; Miller, P.; Olofsson, J.; Poska, A.; Rundgren, M.; Smith, B.; Strandberg, G.; Fyfe, R.; Nielsen, A. B.; Alenius, T.; Balakauskas, L.; Barnekow, L.; Birks, H. J. B.; Bjune, A.; Bjorkman, L.; Giesecke, T.; Hjelle, K.; Kalnina, L.; Kangur, M.; van der Knaap, W. O.; Koff, T.; Lageras, P.; Latalowa, M.; Leydet, M.; Lechterbeck, J.; Lindbladh, M.; Odgaard, B.; Peglar, S.; Segerstrom, U.; von Stedingk, H.; Seppä, H. (2010)
  • Bacour, C.; Maignan, F.; MacBean, N.; Porcar-Castell, A.; Flexas, J.; Frankenberg, C.; Peylin, P.; Chevallier, F.; Vuichard, N.; Bastrikov, V. (2019)
    Abstract Over the last few years, solar-induced chlorophyll fluorescence (SIF) observations from space have emerged as a promising resource for evaluating the spatio-temporal distribution of gross primary productivity (GPP) simulated by global terrestrial biosphere models. SIF can be used to improve GPP simulations by optimizing critical model parameters through statistical Bayesian data assimilation techniques. A prerequisite is the availability of a functional link between GPP and SIF in terrestrial biosphere models. Here we present the development of a mechanistic SIF observation operator in the ORCHIDEE (Organizing Carbon and Hydrology In Dynamic Ecosystems) terrestrial biosphere model. It simulates the regulation of photosystem II fluorescence quantum yield at the leaf level thanks to a novel parameterization of non-photochemical quenching as a function of temperature, photosynthetically active radiation, and normalized quantum yield of photochemistry. It emulates the radiative transfer of chlorophyll fluorescence to the top of the canopy using a parametric simplification of the SCOPE (Soil Canopy Observation Photosynthesis Energy) model. We assimilate two years of monthly OCO-2 (Orbiting Carbon Observatory-2) SIF product at 0.5° (2015?2016) to optimize ORCHIDEE photosynthesis and phenological parameters over an ensemble of grid points for all plant functional types. The impact on the simulated GPP is considerable with a large decrease of the global scale budget by 28 GtC/year over the period 1990?2009. The optimized GPP budget (134/136 GtC/year over 1990?2009/2001?2009) remarkably agrees with independent GPP estimates, FLUXSAT (137 GtC/year over 2001?2009) in particular and FLUXCOM (121 GtC/year over 1990?2009). Our results also suggest a biome dependency of the SIF-GPP relationship that needs to be improved for some plant functional types.
  • Mäkela, Jarmo; Knauer, Juergen; Aurela, Mika; Black, Andrew; Heimann, Martin; Kobayashi, Hideki; Lohila, Annalea; Mammarella, Ivan; Margolis, Hank; Markkanen, Tiina; Susiluoto, Jouni; Thum, Tea; Viskari, Toni; Zaehle, Soenke; Aalto, Tuula (2019)
    We calibrated the JSBACH model with six different stomatal conductance formulations using measurements from 10 FLUXNET coniferous evergreen sites in the boreal zone. The parameter posterior distributions were generated by the adaptive population importance sampler (APIS); then the optimal values were estimated by a simple stochastic optimisation algorithm. The model was constrained with in situ observations of evapotranspiration (ET) and gross primary production (GPP). We identified the key parameters in the calibration process. These parameters control the soil moisture stress function and the overall rate of carbon fixation. The JSBACH model was also modified to use a delayed effect of temperature for photosynthetic activity in spring. This modification enabled the model to correctly reproduce the springtime increase in GPP for all conifer sites used in this study. Overall, the calibration and model modifications improved the coefficient of determination and the model bias for GPP with all stomatal conductance formulations. However, only the coefficient of determination was clearly improved for ET. The optimisation resulted in best performance by the Bethy, Ball-Berry, and the Friend and Kiang stomatal conductance models. We also optimised the model during a drought event at a Finnish Scots pine forest site. This optimisation improved the model behaviour but resulted in significant changes to the parameter values except for the unified stomatal optimisation model (USO). Interestingly, the USO demonstrated the best performance during this event.
  • Trondman, A. -K.; Gaillard, M. -J.; Mazier, F.; Sugita, S.; Fyfe, R.; Nielsen, A. B.; Twiddle, C.; Barratt, P.; Birks, H. J. B.; Bjune, A. E.; Bjorkman, L.; Brostrom, A.; Caseldine, C.; David, R.; Dodson, J.; Doerfler, W.; Fischer, E.; van Geel, B.; Giesecke, T.; Hultberg, T.; Kalnina, L.; Kangur, M.; van der Knaap, P.; Koff, T.; Kunes, P.; Lageras, P.; Latalowa, M.; Lechterbeck, J.; Leroyer, C.; Leydet, M.; Lindbladh, M.; Marquer, L.; Mitchell, F. J. G.; Odgaard, B. V.; Peglar, S. M.; Persson, T.; Poska, A.; Roesch, M.; Seppä, H.; Veski, S.; Wick, L. (2015)
    We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1 degrees x1 degrees spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.
  • Liu, Yuli; Zhou, Guomo; Du, Huaqiang; Berninger, Frank; Mao, Fangjie; Li, Xuejian; Chen, Liang; Cui, Lu; Li, Yangguang; Zhu, Di'en (2018)
    Moso bamboo has large potential to alleviate global warming through carbon sequestration. Since soil respiration (R-s) is a major source of CO2 emissions, we analyzed the dynamics of soil respiration (R-s) and its relation to environmental factors in a Moso bamboo (Phllostachys heterocycla cv. pubescens) forest to identify the relative importance of biotic and abiotic drivers of respiration. Annual average R(s )was 44.07 t CO2 ha(-1) a(-1) R-s correlated significantly with soil temperature (P <0.01), which explained 69.7% of the variation in R-s at a diurnal scale. Soil moisture was correlated significantly with R-s on a daily scale except not during winter, indicating it affected R-s. A model including both soil temperature and soil moisture explained 93.6% of seasonal variations in R-s. The relationship between R-s and soil temperature during a day showed a clear hysteresis. R-s was significantly and positively (P <0.01) related to gross ecosystem productivity and leaf area index, demonstrating the significance of biotic factors as crucial drivers of R-s.
  • Fraixedas, Sara; Linden, Andreas; Meller, Kalle; Lindström, Åke; Keiss, Oskars; Kålås, John Atle; Husby, Magne; Leivits, Agu; Leivits, Meelis; Lehikoinen, Aleksi (2017)
    Northern European peatlands are important habitats for biological conservation because they support rich biodiversity and unique species compositions. However, historical management of peatland habitats has had negative consequences for biodiversity and their degradation remains a major conservation concern. Despite increasing awareness of the conservation value of peatlands, the statuses and ecological requirements of peat land species have remained largely understudied. Here, we first analysed temporal trends of Northern European peatland birds to document the status of their populations using bird data from five different countries. Second, we used Finnish monitoring data to assess habitat preferences of peatland bird species, hence helping to target conservation to the most relevant habitat types. There was a general decline of 40% in Northern European peatland bird population sizes in 1981-2014 (speed of decline 1.5%/year) largely driven by Finland, where populations declined almost 50% (2.0% annual decline). In Sweden and Norway, peatland bird populations declined by 20% during 1997-2014 (1.0% annual decline). In contrast, southern populations in Estonia and Latvia, where the majority of open peatlands are protected, showed a 40% increase during 1981-2014 (1.0% annual increase). The most important habitat characteristics preferred by common peatland species in Finland were openness and low tree height, while wetness proved to be an important feature for waders. Drainage of peatlands had clear negative effects on the densities of many species, with the only exception of rustic bunting, which specializes on edge habitats. Our findings call for more effective conservation actions in Northern European peatland habitats, especially in Finland where peatland drainage represents a major threat to biodiversity.
  • Treat, Claire C.; Kleinen, Thomas; Broothaerts, Nils; Dalton, April S.; Dommain, Rene; Douglas, Thomas A.; Drexler, Judith Z.; Finkelstein, Sarah A.; Grosse, Guido; Hope, Geoffrey; Hutchings, Jack; Jones, Miriam C.; Kuhry, Peter; Lacourse, Terri; Lahteenoja, Outi; Loisel, Julie; Notebaert, Bastiaan; Payne, Richard J.; Peteet, Dorothy M.; Sannel, A. Britta K.; Stelling, Jonathan M.; Strauss, Jens; Swindles, Graeme T.; Talbot, Julie; Tarnocai, Charles; Verstraeten, Gert; Williams, Christopher J.; Xia, Zhengyu; Yu, Zicheng; Väliranta, Minna; Hattestrand, Martina; Alexanderson, Helena; Brovkin, Victor (2019)
    Glacial-interglacial variations in CO2 and methane in polar ice cores have been attributed, in part, to changes in global wetland extent, but the wetland distribution before the Last Glacial Maximum (LGM, 21 ka to 18 ka) remains virtually unknown. We present a study of global peatland extent and carbon (C) stocks through the last glacial cycle (130 ka to present) using a newly compiled database of 1,063 detailed stratigraphic records of peat deposits buried by mineral sediments, as well as a global peatland model. Quantitative agreement between modeling and observations shows extensive peat accumulation before the LGM in northern latitudes (> 40 degrees N), particularly during warmer periods including the last interglacial (130 ka to 116 ka, MIS 5e) and the interstadial (57 ka to 29 ka, MIS 3). During cooling periods of glacial advance and permafrost formation, the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent, thickness, and modeled C stocks by 70 to 90% from warmer times. Tropical peatland extent and C stocks show little temporal variation throughout the study period. While the increased burial of northern peats was correlated with cooling periods, the burial of tropical peat was predominately driven by changes in sea level and regional hydrology. Peat burial by mineral sediments represents a mechanism for long-term terrestrial C storage in the Earth system. These results show that northern peatlands accumulate significant C stocks during warmer times, indicating their potential for C sequestration during the warming Anthropocene.