Atmospheric deposition, CO2, and change in the land carbon sink
Fernández-Martínez, M. ; Vicca, S. ; Janssens, I.A. ; Ciais, P. ; Obersteiner, M. ; Bartrons, M. ; Sardans, Jordi ; Verger, Aleixandre ; Canadell, J.G. ; Chevallier, F. ; Wang, X. ; Bernhofer, C. ; Curtis, P.S. ; Gianelle, D. ; Grünwald, T. ; Heinesch, B. ; Ibrom, A. ; Knohl, A. ; Laurila, T. ; Law, Beverly E. ; Limousin, J.M. ; Longdoz, B. ; Loustau, D. ; Mammarella, I. ; Matteucci, G. ; Monson, R.K. ; Montagnani, L. ; Moors, E.J. ; Munger, J.W. ; Papale, D. ; Piao, S.L. ; Peñuelas, J. - \ 2017
Scientific Reports 7 (2017). - ISSN 2045-2322 - 13 p.
Concentrations of atmospheric carbon dioxide (CO2) have continued to increase whereas atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades. Using time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models, we found that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011. Statistical models indicated that increasing atmospheric CO2 was the most important factor driving the increasing strength of carbon sinks in these forests. We also found that the reduction of sulphur deposition in Europe and the USA lead to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. Our findings support the hypothesis of a general CO2-fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions. Our results show the need to include the effects of changing atmospheric composition, beyond CO2, to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modelling.
Forest summer albedo is sensitive to species and thinning: how should we account for this in Earth system models?
Otto, J. ; Berveiller, D. ; Bréon, F.M. ; Delpierre, N. ; Geppert, G. ; Granier, A. ; Jans, W.W.P. ; Knohl, A. ; Schelhaas, M.J. ; Moors, E.J. - \ 2014
Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 2411 - 2427.
leaf-area index - boreal forest - reflectance models - canopy reflectance - carbon-cycle - climate - radiation - stands - simulations - variability
Although forest management is one of the instruments proposed to mitigate climate change, the relationship between forest management and canopy albedo has been ignored so far by climate models. Here we develop an approach that could be implemented in Earth system models. A stand-level forest gap model is combined with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning on summertime canopy albedo. This approach reveals which parameter has the largest affect on summer canopy albedo: we examined the effects of three forest species (pine, beech, oak) and four thinning strategies with a constant forest floor albedo (light to intense thinning regimes) and five different solar zenith angles at five different sites (40° N 9° E–60° N 9° E). During stand establishment, summertime canopy albedo is driven by tree species. In the later stages of stand development, the effect of tree species on summertime canopy albedo decreases in favour of an increasing influence of forest thinning. These trends continue until the end of the rotation, where thinning explains up to 50% of the variance in near-infrared albedo and up to 70% of the variance in visible canopy albedo. The absolute summertime canopy albedo of all species ranges from 0.03 to 0.06 (visible) and 0.20 to 0.28 (near-infrared); thus the albedo needs to be parameterised at species level. In addition, Earth system models need to account for forest management in such a way that structural changes in the canopy are described by changes in leaf area index and crown volume (maximum change of 0.02 visible and 0.05 near-infrared albedo) and that the expression of albedo depends on the solar zenith angle (maximum change of 0.02 visible and 0.05 near-infrared albedo). Earth system models taking into account these parameters would not only be able to examine the spatial effects of forest management but also the total effects of forest management on climate.
Temporal and among-site variability of inherent water use efficiency at the ecosystem level
Beer, C. ; Ciais, P. ; Reichstein, M. ; Baldocchi, D. ; Law, B.E. ; Papale, D. ; Soussana, J.F. ; Ammann, C. ; Buchmann, N. ; Frank, D. ; Gianelle, D. ; Janssens, I.A. ; Knohl, A. ; Kostner, B. ; Moors, E.J. ; Roupsard, O. ; Verbeeck, H. ; Vesala, T. ; Williams, C.A. ; Wohlfahrt, G. - \ 2009
Global Biogeochemical Cycles 23 (2009). - ISSN 0886-6236 - 13
watergebruiksrendement - kooldioxide - waterdampbeweging - terrestrische ecosystemen - atmosfeer - koolstofcyclus - water use efficiency - carbon dioxide - water vapour movement - terrestrial ecosystems - atmosphere - carbon cycle - scots pine forest - co2 exchange - carbon-dioxide - eddy covariance - central germany - ponderosa pine - canopy-scale - aspen forest - beech forest - time scales
Half-hourly measurements of the net exchanges of carbon dioxide and water vapor between terrestrial ecosystems and the atmosphere provide estimates of gross primary production (GPP) and evapotranspiration (ET) at the ecosystem level and on daily to annual timescales. The ratio of these quantities represents ecosystem water use efficiency. Its multiplication with mean daylight vapor pressure deficit (VPD) leads to a quantity which we call “inherent water use efficiency” (IWUE*). The dependence of IWUE* on environmental conditions indicates possible adaptive adjustment of ecosystem physiology in response to a changing environment. IWUE* is analyzed for 43 sites across a range of plant functional types and climatic conditions. IWUE* increases during short-term moderate drought conditions. Mean annual IWUE* varied by a factor of 3 among all sites. This is partly explained by soil moisture at field capacity, particularly in deciduous broad-leaved forests. Canopy light interception sets the upper limits to canopy photosynthesis, and explains half the variance in annual IWUE* among herbaceous ecosystems and evergreen needle-leaved forests. Knowledge of IWUE* offers valuable improvement to the representation of carbon and water coupling in ecosystem process models
Quality control of CarboEurope flux data - Part 1: Coupling footprint analyses with flux data quality assessment to evaluate sites in forest ecosystems
Gockede, M. ; Foken, T. ; Aubinet, M. ; Aurela, M. ; Banza, J. ; Bernhofer, C. ; Bonnefonds, J.M. ; Brunet, Y. ; Carrara, A. ; Clement, R. ; Dellwik, E. ; Elbers, J.A. ; Eugster, W. ; Fuhrer, J. ; Granier, A. ; Grunwald, T. ; Heinsch, B. ; Janssens, I.A. ; Knohl, A. ; Koeble, R. ; Laurila, T. ; Longdoz, B. ; Manca, G. ; Marek, M. ; Markkanen, T. ; Mateus, J. ; Matteucci, G. ; Mauder, M. ; Migliavacca, M. ; Minerbi, S. ; Moncrieff, J. ; Montagnani, L. ; Moors, E.J. ; Ourcival, J.M. ; Papale, D. ; Pereira, J.M. ; Pilegaard, K. ; Pita, G. ; Rambal, S. ; Rebmann, C. ; Rodrigues, A. ; Rotenberg, E. ; Sanz, M.J. ; Sedlak, P. ; Seufert, G. ; Siebicke, L. ; Soussana, J.F. ; Valentini, R. ; Vesala, T. ; Verbeeck, H. ; Yakir, D. - \ 2008
Biogeosciences 5 (2008)2. - ISSN 1726-4170 - p. 433 - 450.
warmtestroming - eddy-covariantie - gegevensanalyse - ecosystemen - bossen - atmosferische grenslaag - heat flow - eddy covariance - data analysis - ecosystems - forests - atmospheric boundary-layer - eddy covariance measurements - water-vapor - boundary-layer - heat-flux - turbulence statistics - correlation systems - stochastic-models - sonic anemometer - surface fluxes - carbon-dioxide
We applied a site evaluation approach combining Lagrangian Stochastic footprint modeling with a quality assessment approach for eddy-covariance data to 25 forested sites of the CarboEurope-IP network. The analysis addresses the spatial representativeness of the flux measurements, instrumental effects on data quality, spatial patterns in the data quality, and the performance of the coordinate rotation method. Our findings demonstrate that application of a footprint filter could strengthen the CarboEurope-IP flux database, since only one third of the sites is situated in truly homogeneous terrain. Almost half of the sites experience a significant reduction in eddy-covariance data quality under certain conditions, though these effects are mostly constricted to a small portion of the dataset. Reductions in data quality of the sensible heat flux are mostly induced by characteristics of the surrounding terrain, while the latent heat flux is subject to instrumentation-related problems. The Planar-Fit coordinate rotation proved to be a reliable tool for the majority of the sites using only a single set of rotation angles. Overall, we found a high average data quality for the CarboEurope-IP network, with good representativeness of the measurement data for the specified target land cover types.
Linking flux network measurements to continental scale simulations: ecosystem carbon dioxide exchange capacity under non-water-stressed conditions
Owen, K.E. ; Tenhunen, J. ; Reichstein, M. ; Wang, Q. ; Falge, E. ; Geyer, R. ; Xiao, X. ; Stoy, P. ; Ammann, C. ; Arain, A. ; Aubinet, M. ; Aurela, M. ; Bernhofer, C. ; Chojnicki, B.H. ; Granier, A. ; Gruenwald, T. ; Hadley, J. ; Heinesch, B. ; Hollinger, D. ; Knohl, A. ; Kutsch, W. ; Lohila, A. ; Meyers, T. ; Moors, E.J. ; Moureaux, C. ; Pilegaard, K. ; Saigusa, N. ; Verma, S. ; Vesala, T. ; Vogel, C. - \ 2007
Global Change Biology 13 (2007)4. - ISSN 1354-1013 - p. 734 - 760.
kooldioxide - eddy-covariantie - netto ecosysteem uitwisseling - gewassen - bossen - graslanden - wetlands - carbon dioxide - eddy covariance - net ecosystem exchange - crops - forests - grasslands - wetlands - northern temperate grassland - gross primary production - atmosphere co2 exchange - eddy-covariance measurements - daily canopy photosynthesis - danish beech forest - leaf-area index - rain-fed maize - long-term - process model
This paper examines long-term eddy covariance data from 18 European and 17 North American and Asian forest, wetland, tundra, grassland, and cropland sites under non-water-stressed conditions with an empirical rectangular hyperbolic light response model and a single layer two light-class carboxylase-based model. Relationships according to ecosystem functional type are demonstrated between empirical and physiological parameters, suggesting linkages between easily estimated parameters and those with greater potential for process interpretation. Relatively sparse documentation of leaf area index dynamics at flux tower sites is found to be a major difficulty in model inversion and flux interpretation. Therefore, a simplification of the physiological model is carried out for a subset of European network sites with extensive ancillary data. The results from these selected sites are used to derive a new parameter and means for comparing empirical and physiologically based methods across all sites, regardless of ancillary data. The results from the European analysis are then compared with results from the other Northern Hemisphere sites and similar relationships for the simplified process-based parameter were found to hold for European, North American, and Asian temperate and boreal climate zones. This parameter is useful for bridging between flux network observations and continental scale spatial simulations of vegetation/atmosphere carbon dioxide exchange
Evidence for soil water control on carbon and water dynamics in European forests during the extremely dry year: 2003
Granier, A. ; Reichstein, M. ; Bréda, N. ; Janssens, I.A. ; Falge, E. ; Ciais, P. ; Grünwald, T. ; Aubinet, M. ; Berbigier, P. ; Bernhofer, C. ; Buchmann, N. ; Facini, O. ; Grassi, G. ; Heinesch, B. ; Ilvesniemi, H. ; Keronen, P. ; Knohl, A. ; Köstner, B. ; Lagergren, F. ; Lindroth, A. ; Longdoz, B. ; Loustau, D. ; Mateus, J. ; Montagnani, L. ; Nys, C. ; Moors, E.J. ; Papale, D. ; Peiffer, M. ; Pilegaard, K. ; Pita, G. ; Pumpanen, J. ; Rambal, S. ; Rebmann, C. ; Rodrigues, A. ; Seufert, G. ; Tenhunen, J. ; Vesala, T. ; Wang, Q. - \ 2007
Agricultural and Forest Meteorology 143 (2007)1-2. - ISSN 0168-1923 - p. 123 - 145.
droogte - waterbalans - bodemwater - bossen - netto ecosysteem koolstofbalans - west-europa - drought - water balance - soil water - forests - net ecosystem carbon balance - western europe - leaf-area index - fagus-sylvatica l. - ecosystem co2 exchange - sap flow measurements - boreal aspen forest - canopy conductance - deciduous forest - severe drought - beech forest - scots pine
The drought of 2003 was exceptionally severe in many regions of Europe, both in duration and in intensity. In some areas, especially in Germany and France, it was the strongest drought for the last 50 years, lasting for more than 6 months. We used continuous carbon and water flux measurements at 12 European monitoring sites covering various forest ecosystem types and a large climatic range in order to characterise the consequences of this drought on ecosystems functioning. As soil water content in the root zone was only monitored in a few sites, a daily water balance model was implemented at each stand to estimate the water balance terms: trees and understorey transpiration, rainfall interception, throughfall, drainage in the different soil layers and soil water content. This model calculated the onset date, duration and intensity of the soil water shortage (called water stress) using measured climate and site properties: leaf area index and phenology that both determine tree transpiration and rainfall interception, soil characteristics and root distribution, both influencing water absorption and drainage. At sites where soil water content was measured, we observed a good agreement between measured and modelled soil water content. Our analysis showed a wide spatial distribution of drought stress over Europe, with a maximum intensity within a large band extending from Portugal to NE Germany. Vapour fluxes in all the investigated sites were reduced by drought, due to stomatal closure, when the relative extractable water in soil (REW) dropped below ca. 0.4. Rainfall events during the drought, however, typically induced rapid restoration of vapour fluxes. Similar to the water vapour fluxes, the net ecosystem production decreased with increasing water stress at all the sites. Both gross primary production (GPP) and total ecosystem respiration (TER) also decreased when REW dropped below 0.4 and 0.2, for GPP and TER, respectively. A higher sensitivity to drought was found in the beech, and surprisingly, in the broadleaved Mediterranean forests; the coniferous stands (spruce and pine) appeared to be less drought-sensitive. The effect of drought on tree growth was also large at the three sites where the annual tree growth was measured. Especially in beech, this growth reduction was more pronounced in the year following the drought (2004). Such lag effects on tree growth should be considered an important feature in forest ecosystems, which may enhance vulnerability to more frequent climate extremes.
Determinants of terrestrial ecosystem carbon balance inferred from European eddy covariance flux sites
Reichstein, M. ; Papale, D. ; Valentini, R. ; Aubinet, M. ; Bernhofer, C. ; Knohl, A. ; Laurila, T. ; Lindroth, A. ; Moors, E.J. ; Pilegaard, K. ; Seufert, G. - \ 2007
Geophysical Research Letters 34 (2007). - ISSN 0094-8276 - 5
netto ecosysteem koolstofbalans - eddy-covariantie - primaire productie - koolstofcyclus - terrestrische ecosystemen - net ecosystem carbon balance - eddy covariance - primary production - carbon cycle - terrestrial ecosystems - spatial variability - water-vapor - respiration - exchange - forests - climate - productivity - temperature - vegetation - dioxide
Pioneering work in the last century has resulted in a widely accepted paradigm that primary production is strongly positively related to temperature and water availability such that the northern hemispheric forest carbon sink may increase under conditions of global warming. However, the terrestrial carbon sink at the ecosystem level (i.e. net ecosystem productivity, NEP) depends on the net balance between gross primary productivity (GPP) and ecosystem respiration (TER). Through an analysis of European eddy covariance flux data sets, we find that the common climate relationships for primary production do not hold for NEP. This is explained by the fact that decreases in GPP are largely compensated by parallel decreases in TER when climatic factors become more limiting. Moreover, we found overall that water availability was a significant modulator of NEP, while the multivariate effect of mean annual temperature is small and not significant. These results indicate that climate- and particularly temperature-based projections of net carbon balance may be misleading. Future research should focus on interactions between the water and carbon cycles and the effects of disturbances on the carbon balance of terrestrial ecosystems.
Pan-European d13C values of air and organic matter from forest ecosystems
Hemming, D. ; Yakir, D. ; Ambus, P. ; Aurela, M. ; Besson, C. ; Black, K. ; Buchmann, N. ; Burlett, R. ; Cescatti, A. ; Clement, R. ; Gross, P. ; Granier, A. ; Grünwald, T. ; Havrankova, K. ; Janous, D. ; Janssens, I.A. ; Knohl, A. ; Köstner, B. ; Kowalski, A. ; Laurila, T. ; Mata, C. ; Marcolla, B. ; Matteucci, G. ; Moncrieff, J. ; Moors, E.J. ; Osborne, B. ; Santos Pereira, J. ; Pihlatie, M. ; Pilegaard, K. ; Ponti, F. ; Rosova, Z. ; Rossi, F. ; Scartazza, A. ; Vesala, T. - \ 2005
Global Change Biology 11 (2005)7. - ISSN 1354-1013 - p. 1065 - 1093.
carbon-isotope discrimination - tree-ring cellulose - below-ground carbon - fossil-fuel co2 - atmospheric co2 - sampling-network - environmental-regulation - dioxide emissions - soil respiration - root respiration
We present carbon stable isotope, delta C-13, results from air and organic matter samples collected during 98 individual field campaigns across a network of Carboeuroflux forest sites in 2001 (14 sites) and 2002 (16 sites). Using these data, we tested the hypothesis that delta C-13 values derived from large-scale atmospheric measurements and models, which are routinely used to partition carbon fluxes between land and ocean, and potentially between respiration and photosynthesis on land, are consistent with directly measured ecosystem-scale delta C-13 values. In this framework, we also tested the potential of delta C-13 in canopy air and plant organic matter to record regional-scale ecophysiological patterns. Our network estimates for the mean delta C-13 of ecosystem respired CO2 and the related 'discrimination' of ecosystem respiration, delta(er) and Delta(er), respectively, were -25.6 +/- 1.9 parts per thousand and 17.8 +/- 2.0 parts per thousand in 2001 and -26.6 +/- 1.5 parts per thousand and 19.0 +/- 1.6 parts per thousand in 2002. The results were in close agreement with delta C-13 values derived from regional-scale atmospheric measurement programs for 2001, but less so in 2002, which had an unusual precipitation pattern. This suggests that regional-scale atmospheric sampling programs generally capture ecosystem delta C-13 signals over Europe, but may be limited in capturing some of the interannual variations. In 2001, but less so in 2002, there were discernable longitudinal and seasonal trends in delta(er). From west to east, across the network, there was a general enrichment in C-13 (similar to 3 parts per thousand and similar to 1 parts per thousand for the 2 years, respectively) consistent with increasing Gorczynski continentality index for warmer and drier conditions. In 2001 only, seasonal C-13 enrichment between July and September, followed by depletion in November (from about -26.0 parts per thousand to -24.5 parts per thousand to -30.0 parts per thousand), was also observed. In 2001, July and August delta(er) values across the network were significantly related to average daytime vapor pressure deficit (VPD), relative humidity (RH), and, to a lesser degree, air temperature (T-a), but not significantly with monthly average precipitation (P-m). In contrast, in 2002 (a much wetter peak season), delta(er) was significantly related with T-a, but not significantly with VPD and RH. The important role of plant physiological processes on delta(er) in 2001 was emphasized by a relatively rapid turnover (between 1 and 6 days) of assimilated carbon inferred from time-lag analyses of delta(er) vs. meteorological parameters. However, this was not evident in 2002. These analyses also noted corresponding diurnal cycles of delta(er) and meteorological parameters in 2001, indicating a rapid transmission of daytime meteorology, via physiological responses, to the delta(er) signal during this season. Organic matter delta C-13 results showed progressive C-13 enrichment from leaves, through stems and roots to soil organic matter, which may be explained by C-13 fractionation during respiration. This enrichment was species dependent and was prominent in angiosperms but not in gymnosperms. delta C-13 values of organic matter of any of the plant components did not well represent short-term delta(er) values during the seasonal cycle, and could not be used to partition ecosystem respiration into autotrophic and heterotrophic components.
Quality analysis applied on eddy covariance measurements at complex forest sites using footprint modelling
Rebmann, C. ; Göckede, M. ; Foken, T. ; Aubinet, M. ; Aurela, M. ; Berbigier, P. ; Bernhofer, C. ; Buchmann, N. ; Carrara, A. ; Cescatti, A. ; Ceulemans, R. ; Clement, R. ; Elbers, J.A. ; Granier, A. ; Grünwald, T. ; Guyon, D. ; Havránková, K. ; Heinesch, B. ; Knohl, A. ; Laurila, T. ; Longdoz, B. ; Marcolla, B. ; Markkanen, T. ; Miglietta, F. ; Moncrieff, J. ; Montagnani, L. ; Moors, E.J. ; Nardino, M. ; Ourcival, J.M. ; Rambal, S. ; Rannik, Ü. ; Rotenberg, E. ; Sedlak, P. ; Unterhuber, G. ; Vesala, T. ; Yakir, D. - \ 2005
Theoretical and Applied Climatology 80 (2005). - ISSN 0177-798X - p. 121 - 141.
carbon sequestration - heterogeneous forest - flux measurements - deciduous forest - beech forest - net carbon - exchange - co2 - atmosphere - balance
Measuring turbulent fluxes with the eddy covariance method has become a widely accepted and powerful tool for the determination of long term data sets for the exchange of momentum, sensible and latent heat, and trace gases such as CO2 between the atmosphere and the underlying surface. Several flux networks developed continuous measurements above complex terrain, e.g. AmeriFlux and EUROFLUX, with a strong focus on the net exchange of CO2 between the atmosphere and the underlying surface. Under many conditions basic assumptions for the eddy covariance method in its simplified form, such as stationarity of the flow, homogeneity of the surface and fully developed turbulence of the flow field, are not fulfilled. To deal with non-ideal conditions which are common at many FLUXNET sites, quality tests have been developed to check if these basic theoretical assumptions are valid. In the framework of the CARBOEUROFLUX project, we combined quality tests described by Foken and Wichura (1996) with the analytical footprint model of Schmid (1997). The aim was to identify suitable wind sectors and meteorological conditions for flux measurements. These tools were used on data of 18 participating sites. Quality tests were applied on the fluxes of momentum, sensible and latent heat, and on the CO2-flux, respectively. The influence of the topography on the vertical wind component was also checked. At many sites the land use around the flux towers is not homogeneous or the fetch may not be large enough. So the relative contribution of the land use type intended to be measured was also investigated. Thus the developed tool allows comparative investigations of the measured turbulent fluxes at different sites if using the same technique and algorithms for the determination of the fluxes as well as analyses of potential problems caused by influences of the surrounding land use patterns