Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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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.

Winter respiratory C losses provide explanatory power for net ecosystem productivity
Haeni, M. ; Zweifel, R. ; Eugster, W. ; Gessler, A. ; Zielis, S. ; Bernhofer, C. ; Carrara, A. ; Grünwald, T. ; Havránková, K. ; Heinesch, B. ; Marek, M. ; Moors, E. ; Schelhaas, M.J. ; Buchmann, N. - \ 2017
Journal of Geophysical Research: Biogeosciences 122 (2017)1. - ISSN 2169-8953 - p. 243 - 260.
carbon sink - carbon source - CO exchange - eddy covariance - growing season length - winter respiration

Accurate predictions of net ecosystem productivity (NEPc) of forest ecosystems are essential for climate change decisions and requirements in the context of national forest growth and greenhouse gas inventories. However, drivers and underlying mechanisms determining NEPc (e.g., climate and nutrients) are not entirely understood yet, particularly when considering the influence of past periods. Here we explored the explanatory power of the compensation day (cDOY)—defined as the day of year when winter net carbon losses are compensated by spring assimilation—for NEPc in 26 forests in Europe, North America, and Australia, using different NEPc integration methods. We found cDOY to be a particularly powerful predictor for NEPc of temperate evergreen needleleaf forests (R2 = 0.58) and deciduous broadleaf forests (R2 = 0.68). In general, the latest cDOY correlated with the lowest NEPc. The explanatory power of cDOY depended on the integration method for NEPc, forest type, and whether the site had a distinct winter net respiratory carbon loss or not. The integration methods starting in autumn led to better predictions of NEPc from cDOY then the classical calendar method starting 1 January. Limited explanatory power of cDOY for NEPc was found for warmer sites with no distinct winter respiratory loss period. Our findings highlight the importance of the influence of winter processes and the delayed responses of previous seasons' climatic conditions on current year's NEPc. Such carry-over effects may contain information from climatic conditions, carbon storage levels, and hydraulic traits of several years back in time.

Matching the phenology of Net Ecosystem Exchange and vegetation indices estimated with MODIS and FLUXNET in-situ observations
Balzarolo, M. ; Vicca, S. ; Nguy-Robertson, A.L. ; Bonal, D. ; Elbers, J.A. ; Fu, Y.H. ; Grünwald, T. ; Horemans, J.A. ; Papale, D. ; Peñuelas, J. ; Suyker, A. ; Veroustraete, F. - \ 2016
Remote Sensing of Environment 174 (2016). - ISSN 0034-4257 - p. 290 - 300.
Net Ecosystem Exchange (NEE) - Phenology - Plant functional types (PFT's) - Start of growing season (SGS) - Start of net carbon uptake (SGS) - Vegetation indices (VI's)

Shifts in ecosystem phenology play an important role in the definition of inter-annual variability of net ecosystem carbon uptake. A good estimate at the global scale of ecosystem phenology, mainly that of photosynthesis or gross primary productivity (GPP), may be provided by vegetation indices derived from MODIS satellite image data.However, the relationship between the start date of a growing (or greening) season (SGS) when derived from different vegetation indices (VI's), and the starting day of carbon uptake is not well elucidated. Additionally, the validation of existing phenology data with in-situ measurements is largely missing. We have investigated the possibility to use different VI's to predict the starting day of the growing season for 28 FLUXNET sites as well as MODIS data. This analysis included main plant functional types (PFT's).Of all VI's taken into account in this paper, the NDVI (Normalized Difference Vegetation Index) shows the highest correlation coefficient for the relationship between the starting day of the growing season as observed with MODIS and in-situ observations. However, MODIS observations elicit a 20-21 days earlier SGS date compared to in-situ observations. The prediction for the NEE start of the growing season diverges when using different VI's, and seems to depend on the amplitude for carbon and VI and on PFT. The optimal VI for estimation of a SGS date was PFT-specific - for example the WRDVI for cropland, but the MODIS NDVI performed best when applied as an estimator for Net Ecosystem Exchange and when considering all PFT's pooled.

Evapotranspiration amplifies European summer drought
Teuling, A.J. ; Loon, A.F. van; Seneviratne, S.I. ; Lehner, I. ; Aubinet, M. ; Heinesch, B. ; Bernhofer, C. ; Grünwald, T. ; Prasse, H. ; Spank, U. - \ 2013
Geophysical Research Letters 40 (2013)10. - ISSN 0094-8276 - p. 2071 - 2075.
forest - simulations - exchange - carbon - scale
Drought is typically associated with a lack of precipitation, whereas the contribution of evapotranspiration and runoff to drought evolution is not well understood. Here we use unique long-term observations made in four headwater catchments in central and western Europe to reconstruct storage anomalies and study the drivers of storage anomaly evolution during drought. We provide observational evidence for the “drought-paradox” in that region: a consistent and significant increase in evapotranspiration during drought episodes, which acts to amplify the storage anomalies. In contrast, decreases in runoff act to limit storage anomalies. Our findings stress the need for the correct representation of evapotranspiration and runoff processes in drought indices.
Estimating noctural ecosystem respiration from the vertical turbulent flux and change in storange of CO2
Gorsel, E. van; Delpierre, N. ; Leuning, R. ; Black, A. ; Munger, J.W. ; Wofsy, S. ; Aubinet, M. ; Feigenwinter, C. ; Beringer, J. ; Bonal, D. ; Chen, B. ; Chen, J. ; Clement, R. ; Davis, K.J. ; Desai, A.R. ; Dragoni, D. ; Etzold, S. ; Grünwald, T. ; Gu, L. ; Heinesch, B. ; Hutyra, L.R. ; Jans, W.W.P. ; Kutsch, W. ; Law, B.E. ; Leclerc, Y. ; Mammarella, I. ; Montagnani, L. ; Noormets, A. ; Rebmann, C. ; Wharton, S. - \ 2009
Agricultural and Forest Meteorology 149 (2009)11. - ISSN 0168-1923 - p. 1919 - 1930.
ecosystemen - ademhaling - meettechnieken - nacht - kooldioxide - eddy-covariantie - micrometeorologie - luchtstroming - netto ecosysteem koolstofbalans - ecosystems - respiration - measurement techniques - night - carbon dioxide - eddy covariance - micrometeorology - air flow - net ecosystem carbon balance - eddy covariance measurements - temperate deciduous forest - carbon-dioxide exchange - ponderosa pine forests - long-term measurements - douglas-fir stand - old-growth forest - soil respiration - pacific-northwest - difficult conditions
Micrometeorological measurements of nighttime ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397–403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (FC) and change in storage (FS) of CO2 in the few hours after sundown. The sum of FC and FS reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration RRmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of Fc + Fs extrapolated to zero light, RLRC, and (3) with a detailed process-based forest ecosystem model, Rcast. At most sites respiration rates estimated using the u*-filter, Rust, were smaller than RRmax and RLRC. Agreement of our approach with independent measurements indicates that RRmax provides an excellent estimate of nighttime ecosystem respiration.
Quality control of CarboEurope flux data - Part II: Inter-comparison of eddy-covariance soltware
Mauder, M. ; Foken, T. ; Clement, R. ; Elbers, J.A. ; Eugster, W. ; Grünwald, T. ; Heusinkveld, B.G. ; Kolle, O. - \ 2007
Biogeosciences Discussions 4 (2007)6. - ISSN 1810-6277 - p. 4067 - 4099.
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.
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
Analyzing the ecosystem carbon dynamics of four European coniferous forests using a biogeochemistry model
Churkina, G. ; Tenhunen, J. ; Thornton, P. ; Falge, E. ; Elbers, J.A. ; Erhard, M. ; Grünwald, T. ; Kowalski, A. ; Rannik, Ü. ; Sprinz, D. - \ 2003
Ecosystems 6 (2003)2. - ISSN 1432-9840 - p. 168 - 184.
time climate variability - daily solar-radiation - global change - gap models - terrestrial ecosystems - atmospheric transport - regional applications - deciduous forest - nitrogen budgets - satellite data
This paper provides the first steps toward a regional-scale analysis of carbon (C) budgets. We explore the ability of the ecosystem model BIOME-BGC to estimate the daily and annual C dynamics of four European coniferous forests and shifts in these dynamics in response to changing environmental conditions. We estimate uncertainties in the model results that arise from incomplete knowledge of site management history (for example, successional stage of forest). These uncertainties are especially relevant in regional-scale simulations, because this type of information is difficult to obtain. Although the model predicted daily C and water fluxes reasonably well at all sites, it seemed to have a better predictive capacity for the photosynthesis-related processes than for respiration. Leaf area index (LAI) was modeled accurately at two sites but overestimated at two others (as a result of poor long-term climate drivers and uncertainties in model parameterization). The overestimation of LAI (and consequently gross photosynthetic production (GPP)), in combination with reasonable estimates of the daily net ecosystem productivity (NEP) of those forests, also illustrates the problem with modeled respiration. The model results suggest that all four European forests have been net sinks of C at the rate of 100-300 gC/m2/y and that this C sequestration capacity would be 30%-70% lower without increasing nitrogen (N) deposition and carbon dioxide (CO2) concentrations. The magnitude of the forest responses was dependent not only on the rate of changes in environmental factors, but also on site-specific conditions such as climate and soil depth. We estimated that the modeled C exchange at the study sites was reduced by 50%-100% when model simulations were performed for climax forests rather than regrowing forests. The estimates of water fluxes were less sensitive to different initializations of state variables or environmental change scenarios than C fluxes.
Phase and amplitude of ecosystem carbon release and uptake potentials as derived from FLUXNET measurements
Falge, E. ; Tenhunen, J. ; Baldocchi, D. ; Aubinet, M. ; Bakwin, P. ; Berbigier, P. ; Bernhofer, C. ; Bonnefond, J.M. ; Burba, G. ; Clement, R. ; Davis, K.J. ; Elbers, J.A. ; Falk, M. ; Goldstein, A.H. ; Grelle, A. ; Granier, A. ; Grünwald, T. ; Gudmundsson, J. ; Hollinger, D. ; Janssens, I.A. ; Keronen, P. ; Kowalski, A.S. ; Katul, G. ; Law, B.E. ; Malhi, Y. ; Meyers, T. ; Monson, R.K. ; Moors, E.J. ; Munger, J.W. - \ 2002
Agricultural and Forest Meteorology 113 (2002)1-4. - ISSN 0168-1923 - p. 75 - 95.
bos - broeikaseffect - ecologie - energiebalans - klimaat - koolstofhuishouding - meteorologie - vegetatie
g: should we doubt "surprising" results?; a reply to Piovesan & Adams
Jarvis, P.G. ; Dolman, A.J. ; Schulze, E.D. ; Matteucci, G. ; Kowalski, A.S. ; Ceulemans, R. ; Rebmann, C. ; Moors, E.J. ; Granier, A. ; Gross, P. ; Jensen, N.O. ; Pilegaard, K. ; Lindroth, A. ; Grelle, A. ; Bernhofer, C. ; Grünwald, T. ; Aubinet, M. ; Vesala, T. ; Rannik, Ü. ; Berbigier, P. ; Loustau, D. ; Gudmundson, J. ; Ibrom, A. ; Morgenstern, K. ; Clement, R. ; Moncrieff, J. ; Montagnani, L. ; Minerbi, S. ; Valentini, R. - \ 2001
Journal of Vegetation Science 12 (2001)1. - ISSN 1100-9233 - p. 145 - 150.
bosecologie - koolstofhuishouding
This paper responds to the Forum contribution by Piovesan & Adams (2000) who criticized the results obtained by the EUROFLUX network on carbon fluxes of several European forests. The major point of criticism was that the data provided by EUROFLUX are inconsistent with current scientific understanding. It is argued that understanding the terrestrial global carbon cycle requires more than simply restating what was known previously, and that Piovesan & Adams have not been able to show any major conflicts between our findings and ecosystem or atmospheric-transport theories.
Productivity overshadows temperature in determining soil and ecosystem respiration across European forests
Janssens, I.A. ; Lankreijer, H. ; Matteucci, G. ; Kowalski, A.S. ; Buchmann, N. ; Epron, D. ; Pilegaard, K. ; Kutsch, W. ; Longdoz, B. ; Grünwald, T. ; Montagnani, L. ; Dore, S. ; Rebmann, C. ; Moors, E.J. ; Grelle, A. ; Rannik, Ü. ; Morgenstern, K. ; Oltchev, S. ; Clement, R. ; Gudmundsson, J. ; Minerbi, S. ; Berbigier, P. ; Ibrom, A. ; Moncrieff, J. ; Aubinet, M. ; Bernhofer, C. ; Jensen, N.O. ; Vesala, T. ; Granier, A. - \ 2001
Global Change Biology 7 (2001)3. - ISSN 1354-1013 - p. 269 - 278.
This paper presents CO2 flux data from 18 forest ecosystems, studied in the European Union funded EUROFLUX project. Overall, mean annual gross primary productivity (GPP, the total amount of carbon (C) fixed during photosynthesis) of these forests was 1380 ± 330 gC m-2y-1 (mean ± SD). On average, 80 f GPP was respired by autotrophs and heterotrophs and released back into the atmosphere (total ecosystem respiration, TER = 1100 ± 260 gC m-2y-1). Mean annual soil respiration (SR) was 760 ± 340 gC m-2y-1 (55 f GPP and 69 f TER). Among the investigated forests, large differences were observed in annual SR and TER that were not correlated with mean annual temperature. However, a significant correlation was observed between annual SR and TER and GPP among the relatively undisturbed forests. On the assumption that (i) root respiration is constrained by the allocation of photosynthates to the roots, which is coupled to productivity, and that (ii) the largest fraction of heterotrophic soil respiration originates from decomposition of young organic matter (leaves, fine roots), whose availability also depends on primary productivity, it is hypothesized that differences in SR among forests are likely to depend more on productivity than on temperature. At sites where soil disturbance has occurred (e.g. ploughing, drainage), soil espiration was a larger component of the ecosystem C budget and deviated from the relationship between annual SR (and TER) and GPP observed among the less-disturbed forests. At one particular forest, carbon losses from the soil were so large, that in some years the site became a net source of carbon to the atmosphere. Excluding the disturbed sites from the present analysis reduced mean SR to 660 ± 290 gC m-2y-1, representing 49 f GPP and 63 f TER in the relatively undisturbed forest ecosystems.
Gap filling strategies for long term energy flux data sets
Falge, E. ; Baldocchi, D. ; Olson, R. ; Anthoni, P. ; Aubinet, M. ; Bernhofer, C. ; Burba, G. ; Ceulemans, R. ; Clement, R. ; Dolman, H. ; Granier, A. ; Gross, P. ; Grünwald, T. ; Hollinger, D. ; Jensen, N.O. ; Katul, G. ; Keronen, P. ; Kowalski, A. ; Lai, C.T. ; Law, B.E. ; Meyers, T. ; Moncrieff, J. ; Moors, E.J. ; Munger, J.W. ; Pilegaard, K. ; Rebmann, C. ; Suyker, A. ; Tenhunen, J. ; Tu, K. - \ 2001
Agricultural and Forest Meteorology 107 (2001)1. - ISSN 0168-1923 - p. 71 - 77.
At present a network of over 100 field sites are measuring carbon dioxide, water vapor and sensible heat fluxes between the biosphere and atmosphere, on a nearly continuous basis. Gaps in the long term measurements of evaporation and sensible heat flux must be filled before these data can be used for hydrological and meteorological applications. We adapted methods of gap filling for NEE (net ecosystem exchange of carbon) to energy fluxes and applied them to data sets available from the EUROFLUX and AmeriFlux eddy covariance databases. The average data coverage for the sites selected was 69% and 75% for latent heat (λE) and sensible heat (H). The methods were based on mean diurnal variations (half-hourly binned means of fluxes based on previous and subsequent days, MDV) and look-up tables for fluxes during assorted meteorological conditions (LookUp), and the impact of different gap filling methods on the annual sum of λE and H is investigated. The difference between annual λE filled by MDV and λE filled by LookUp ranged from - 120 to 210 MJ m-2 per year, i.e. -48 to +86 mm per year, or -13 to +39% of the annual sum. For annual sums of H differences between -140 and + 140 MJ m-2 per year or -12 to +19% of the annual sum were found.
Gap filling strategies for defensible annual sums of net ecosystem exchange
Falge, E. ; Baldocchi, D. ; Olson, R. ; Anthoni, P. ; Aubinet, M. ; Bernhofer, C. ; Burba, G. ; Ceulemans, R. ; Clement, R. ; Dolman, H. ; Granier, A. ; Gross, P. ; Grünwald, T. ; Hollinger, D. ; Jensen, N.O. ; Katul, G. ; Keronen, P. ; Kowalski, A. ; Lai, C.T. ; Law, B.E. ; Meyers, T. ; Moncrieff, J. ; Moors, E.J. ; Munger, J.W. ; Pilegaard, K. ; Rebmann, C. ; Suyker, A. ; Tenhunen, J. ; Tu, K. - \ 2001
Agricultural and Forest Meteorology 107 (2001)1. - ISSN 0168-1923 - p. 43 - 69.
Heightened awareness of global change issues within both science and political communities has increased interest in using the global network of eddy covariance flux towers to more fully understand the impacts of natural and anthropogenic phenomena on the global carbon balance. Comparisons of net ecosystem exchange (FNEE) responses are being made among biome types, phenology patterns, and stress conditions. The comparisons are usually performed on annual sums of FNEE; however, the average data coverage during a year is only 65%. Therefore, robust and consistent gap filling methods are required. We review several methods of gap filling and apply them to data sets available from the EUROFLUX and AmeriFlux databases. The methods are based on mean diurnal variation (MDV), look-up tables (LookUp), and nonlinear regressions (Regr.), and the impact of different gap filling methods on the annual sum of FNEE is investigated. The difference between annual FNEE filled by MDV compared to FNEE filled by Regr. ranged from -45 to +200 g C m-2 per year (MDV-Regr.). Comparing LookUp and Regr. methods resulted in a difference (LookUp-Regr.) ranging from -30 to +150 g C m-2 per year. We also investigated the impact of replacing measurements at night, when turbulent mixing is insufficient. The nighttime correction for low friction velocities (u*) shifted annual FNEE on average by +77 g C m-2 per year, but in certain cases as much as + 185 g C m-2 per year. Our results emphasize the need to standardize gap filling-methods for improving the comparability of flux data products from regional and global flux networks.
Estimates of the annual net carbon and water exchange of forests: the EUROFLUX methodology
Aubinet, M. ; Grelle, A. ; Ibrom, A. ; Rannik, S. ; Moncrieff, J. ; Foken, T. ; Kowalski, A.S. ; Martin, P.H. ; Berbigier, P. ; Bernhofer, C. ; Clement, R. ; Elbers, J.A. ; Granier, A. ; Grünwald, T. ; Morgenstern, K. ; Pilegaard, K. ; Rebmann, C. ; Snijders, W. ; Valentini, R. ; Vesa, T. - \ 2000
Advances in Ecological Research 30 (2000)1. - ISSN 0065-2504 - p. 113 - 175.
Respiration as the main determinant of carbon balance in European forests
Valentini, R. ; Matteucci, G. ; Dolman, A.J. ; Schulze, E.D. ; Rebmann, C. ; Moors, E.J. ; Granier, A. ; Gross, P. ; Jensen, N.O. ; Pilegaard, K. ; Lindroth, A. ; Grelle, A. ; Bernhofer, C. ; Grünwald, T. ; Aubinet, M. ; Ceulemans, R. ; Kowalski, A.S. ; Vesala, T. ; Rannik, Ü. ; Berbigier, P. ; Loustau, D. ; Gudmundsson, J. ; Thorgeirsson, H. ; Ibrom, A. ; Morgenstern, K. ; Clement, R. ; Moncrieff, J. ; Montagnani, L. ; Minerbi, S. ; Jarvis, P.G. - \ 2000
Nature 404 (2000)6780. - ISSN 0028-0836 - p. 861 - 865.
Carbon exchange between the terrestrial biosphere and the atmosphere is one of the key processes that need to be assessed in the context of the Kyoto Protocol. Several studies suggest that the terrestrial biosphere is gaining carbon, but these estimates are obtained primarily by indirect methods, and the factors that control terrestrial carbon exchange, its magnitude and primary locations, are under debate. Here we present data of net ecosystem carbon exchange, collected between 1996 and 1998 from 15 European forests, which confirm that many European forest ecosystems act as carbon sinks. The annual carbon balances range from an uptake of 6.6 tonnes of carbon per hectare per year to a release of nearly 1 t C ha-1 yr-1, with a large variability between forests. The data show a significant increase of carbon uptake with decreasing latitude, whereas the gross primary production seems to be largely independent of latitude. Our observations indicate that, in general, ecosystem respiration determines net ecosystem carbon exchange. Also, for an accurate assessment of the carbon balance in a particular forest ecosystem, remote sensing of the normalized difference vegetation index or estimates based on forest inventories may not be sufficient.
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