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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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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.
Summertime canopy albedo is sensitive to forest thinning
Otto, J. ; Berveiller, D. ; Bréon, F.M. ; Delpierre, N. ; Geppert, G. ; Granier, A. ; Jans, W.W.P. ; Knohl, A. ; Moors, E.J. - \ 2013
Biogeosciences Discussions 10 (2013). - ISSN 1810-6277 - p. 15373 - 15414.
Despite an emerging body of literature linking canopy albedo to forest management, understanding of the process is still fragmented. We combined a stand-level forest gap model with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning, that is removing trees at a certain time during the forest rotation, on summertime canopy albedo. The effects of different forest species (pine, beech, oak) and four thinning strategies (light to intense thinning regimes) were examined. 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 on summertime canopy albedo. These trends continue until the end of the rotation where thinning explains up to 50% of the variance in near-infrared canopy albedo and up to 70% of the variance in visible canopy albedo. More intense thinning lowers the summertime shortwave albedo in the canopy by as much as 0.02 compared to unthinned forest. The structural changes associated with forest thinning can be described by the change in LAI in combination with crown volume. However, forests with identical canopy structure can have different summertime albedo values due to their location: the further north a forest is situated, the more the solar zenith angle increases and thus the higher is the summertime canopy albedo, independent of the wavelength. Despite the increase of absolute summertime canopy albedo values with latitude, the difference in canopy albedo between managed and unmanaged forest decreases with increasing latitude. Forest management thus strongly altered summertime forest albedo.
Effects of species selection and management on forest canopy albedo
Otto, J. ; Berveiller, D. ; Breon, F.M. ; Delpierre, N. ; Geppert, G. ; Granier, A. ; Jans, W.W.P. ; Moors, E.J. ; Schelhaas, M. - \ 2013
Forest management is considered to be one of the more easy to implement instruments available to mitigate climate change as it can lead to increased sequestration of atmospheric carbon dioxide. However, the changes in canopy albedo, and hence surface energy balance, may neutralise or offset the climate benefits of carbon sequestration. Although there is an emerging body of literature linking canopy albedo to management, understanding is still fragmented. We here make use of a generally applicable approach: we combine a stand-level forest gap model with a canopy radiation transfer model and satellite-derived model parameters in order to quantify the effects of forest management on canopy albedo for different forest species and management strategies. The structural changes associated with forest management can be described by the change in LAI in combination with crown volume. However, not only the removal of trees but also the type of understorey affects the canopy albedo. The relationship between the canopy cover and the canopy albedo is explained by the influence of the albedo of the forest floor. A low canopy cover allows more light to penetrate to the forest floor and is more likely to support an abundant understorey vegetation. When the albedo of the understorey vegetation exceeds the albedo of the overstorey canopy, a low canopy cover is likely to result in a high albedo. We find that the most intensive management measures lead to the largest albedo change, which can reach up to 9% compared to unmanaged forest. The choice of species, in combination with thinning, dominates the variation in canopy albedo. During stand establishment, albedo is driven by tree species. Following canopy closure, the effect of tree species on albedo decreases in favour of an increasing importance of forest management on albedo. These trends continue until the end of the rotation where management finally explains up to 80% of the variance in canopy albedo. In summary, forest albedo, and hence surface energy balance, is strongly altered by humans.
Multiresistant Salmonella enterica serovar 4,[5],12:i:- in Europe: a new pandemic strain?
Hopkins, K.L. ; Kirchner, M. ; Guerra, B. ; Granier, A. ; Lucarelli, C. ; Porrero, M.C. ; Jakubczak, A. ; Threlfall, J. ; Mevius, D.J. - \ 2010
Eurosurveillance 15 (2010)22. - ISSN 1025-496X - p. 1 - 9.
antimicrobial resistance genes - molecular characterization - multidrug-resistance - monophasic variant - serotype typhimurium - 4,5,12-i - identification - infections - emergence - carcasses
A marked increase in the prevalence of S. enterica serovar 4,[5],12:i:- with resistance to ampicillin, streptomycin, sulphonamides and tetracyclines (R-type ASSuT) has been noted in food-borne infections and in pigs/pig meat in several European countries in the last ten years. One hundred and sixteen strains of S. enterica serovar 4,[5],12:i:- from humans, pigs and pig meat isolated in England and Wales, France, Germany, Italy, Poland, Spain and the Netherlands were further subtyped by phage typing, pulsed-field gel electrophoresis and multilocus variable number tandem repeat analysis to investigate the genetic relationship among strains. PCR was performed to identify the fljB flagellar gene and the genes encoding resistance to ampicillin, streptomycin, sulphonamides and tetracyclines. Class 1 and 2 integrase genes were also sought. Results indicate that genetically related serovar 4,[5],12:i:- strains of definitive phage types DT193 and DT120 with ampicillin, streptomycin, sulphonamide and tetracycline resistance encoded by blaTEM, strA-strB, sul2 and tet(B) have emerged in several European countries, with pigs the likely reservoir of infection. Control measures are urgently needed to reduce spread of infection to humans via the food chain and thereby prevent the possible pandemic spread of serovar 4,[5],12:i:- of R-type ASSuT as occurred with S. Typhimurium DT104 during the 1990s.
Toward a consistency cross-check of eddy covariance flux-based and biometric estimates of ecosystem carbon balance
Luyssaert, S. ; Reichstein, M. ; Schulze, E.D. ; Janssens, I.A. ; Law, B.E. ; Papale, D. ; Dragoni, D. ; Goulden, M.L. ; Granier, A. ; Kutch, W.L. ; Linder, S. ; Matteucci, G. ; Moors, E.J. ; Munger, J.W. ; Pilegaard, K. ; Saunders, M. ; Falge, E.M. - \ 2009
Global Biogeochemical Cycles 23 (2009). - ISSN 0886-6236 - 13
netto ecosysteem koolstofbalans - schattingen - eddy-covariantie - primaire productie - biometrie - meetsystemen - net ecosystem carbon balance - estimates - eddy covariance - primary production - biometry - measurement systems - net primary production - gross primary production - ponderosa pine forests - mixed hardwood forest - water-vapor exchange - soil co2 efflux - european forests - beech forest - chamber measurements - spatial variability
Quantification of an ecosystem's carbon balance and its components is pivotal for understanding both ecosystem functioning and global cycling. Several methods are being applied in parallel to estimate the different components of the CO2 balance. However, different methods are subject to different sources of error. Therefore, it is necessary that site level component estimates are cross-checked against each other before being reported. Here we present a two-step approach for testing the accuracy and consistency of eddy covariance–based gross primary production (GPP) and ecosystem respiration (Re) estimates with biometric measurements of net primary production (NPP), autotrophic (Ra) and heterotrophic (Rh) respiration. The test starts with closing the CO2 balance to account for reasonable errors in each of the component fluxes. Failure to do so within the constraints will classify the flux estimates on the site level as inconsistent. If the CO2 balance can be closed, the test continues by comparing the closed site level Ra/GPP with the Rh/GPP ratio. The consistency of these ratios is then judged against expert knowledge. Flux estimates of sites that pass both steps are considered consistent. An inconsistent ratio is not necessarily incorrect but provides a signal for careful data screening that may require further analysis to identify the possible biological reasons of the unexpected ratios. We reviewed the literature and found 16 sites, out of a total of 529 research forest sites, that met the data requirements for the consistency test. Thirteen of these sites passed both steps of the consistency cross-check. Subsequently, flux ratios (NPP/GPP, Rh/NPP, Rh/Re, and Re/GPP) were calculated for the consistent sites. Similar ratios were observed at sites which lacked information to check consistency, indicating that the flux data that are currently used for validating models and testing ecological hypotheses are largely consistent across a wide range of site productivities. Confidence in the output of flux networks could be further enhanced if the required fluxes are independently estimated at all sites for multiple years and harmonized methods are used
Impact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana
Bonal, D. ; Bosc, A. ; Ponton, S. ; Goret, J. ; Burban, B. ; Gross, P. ; Bonnefonds, J.M. ; Elbers, J.A. ; Longdoz, B. ; Epron, D. ; Guehl, J. ; Granier, A. - \ 2008
Global Change Biology 14 (2008)8. - ISSN 1354-1013 - p. 1917 - 1933.
ecosystemen - droog seizoen - tropische regenbossen - eddy-covariantie - netto ecosysteem koolstofbalans - atmosferische grenslaag - droogte - frans-guyana - ecosystems - dry season - tropical rain forests - eddy covariance - net ecosystem carbon balance - atmospheric boundary-layer - drought - french guiana - transitional tropical forest - carbon-dioxide uptake - soil co2 efflux - european forests - amazonian ecosystems - respiration - climate - fluxes
The lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEPd) and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (5 °16'54"N, 52 °54'44"W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93-day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 g C m¿2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower REd combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 g C m¿2. Severe drought conditions resulted in even lower REd, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 g C m¿2), emphasizing that environmental conditions, such as during a severe drought, modify the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance
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.
CO2 balance of boreal, temperate, and tropical forests
Luyssaert, S. ; Inglima, I. ; Jungs, M. ; Richardson, A. ; Reichsteins, M. ; Papale, D. ; Piao, S.L. ; Schulzes, E.D. ; Wingate, L. ; Matteucci, G. ; Aragaoss, L. ; Aubinet, M. ; Beers, C. van; Bernhofer, C. ; Black, K.G. ; Bonal, D. ; Bonnefonds, J.M. ; Chambers, J. ; Ciais, P. ; Cook, B. ; Davis, K.J. ; Dolman, A.J. ; Gielen, B. ; Goulden, M. ; Grace, J. ; Granier, A. ; Grelle, A. ; Griffis, T. ; Grunwald, T. ; Guidolotti, G. ; Hanson, P.J. ; Harding, R. ; Hollinger, D.Y. ; Hutyra, L.R. ; Kolari, P. ; Kruijt, B. ; Kutsch, W. ; Lagergren, F. ; Laurila, T. ; Law, B.E. ; Maire, G. Le; Lindroth, A. ; Loustau, D. ; Malhi, Y. ; Mateus, J. ; Migliavacca, M. ; Misson, L. ; Montagnani, L. ; Moncrief, J. ; Moors, E.J. ; Munger, J.W. ; Nikinmaa, E. ; Ollinger, S.V. ; Pita, G. ; Rebmann, C. ; Roupsard, O. ; Saigusa, N. ; Sanz, M.J. ; Seufert, G. ; Sierra, C. ; Smith, M. ; Tang, J. ; Valentini, R. ; Vesala, T. ; Janssens, I.A. - \ 2007
Global Change Biology 13 (2007)12. - ISSN 1354-1013 - p. 2509 - 2537.
net primary production - carbon-dioxide exchange - total soil respiration - eddy-covariance measurements - water-vapor exchange - black spruce forests - ponderosa pine forests - amazonian rain-forest - broad-leaved forest - gross primary production
Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 °C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for.
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 - 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.
Sensitivity of water and carbon fluxes to climate changes from 1960 to 2100 in European forest ecosystems
Davi, H. ; Dufrêne, E. ; Francois, C. ; Maire, G. Le; Loustau, D. ; Bosc, A. ; Rambal, S. ; Granier, A. ; Moors, E.J. - \ 2006
Agricultural and Forest Meteorology 141 (2006)1. - ISSN 0168-1923 - p. 35 - 56.
modeling canopy photosynthesis - elevated co2 concentration - beech forest - temperature response - pine forest - seasonal drought - global radiation - direct component - atmospheric co2 - increasing co2
The effects of climate changes on carbon and water fluxes are quantified using a physiologically multi-layer, process-based model containing a carbon allocation model and coupled with a soil model (CASTANEA). The model is first evaluated on four EUROFLUX sites using eddy covariance data, which provide estimates of carbon and water fluxes at the ecosystem scale. It correctly reproduces the diurnal fluxes and the seasonal pattern. Thereafter simulations were conducted on six French forest ecosystems representative of three climatic areas (oceanic, continental and Mediterranean areas) dominated by deciduous species (Fagus sylvatica, Quercus robur), coniferous species (Pinus pinaster, Pinus sylvestris) or sclerophyllous evergreen species (Quercus ilex). The model is driven by the results of a meteorological model (ARPEGE) following the B2 scenario of IPCC. From 1960 to 2100, the average temperature increases by 3.1 °C (30%) and the rainfall during summer decreases by 68 mm (-27%). For all the sites, between the two periods, the simulations predict on average a gross primary production (GPP) increase of 513 g(C) m-2 (+38%). This increase is relatively steep until 2020, followed by a slowing down of the GPP rise due to an increase of the effect of water stress. Contrary to GPP, the ecosystem respiration (Reco) raises at a constant rate (350 g(C) m-2 i.e. 31% from 1960 to 2100). The dynamics of the net ecosystem productivity (GPP minus Reco) is the consequence of the effect on both GPP and Reco and differs per site. The ecosystems always remain carbon sinks; however the sink strength globally decreases for coniferous (-8%), increases for sclerophyllous evergreen (+34%) and strongly increases for deciduous forest (+67%) that largely benefits by the lengthening of the foliated period. The separately quantified effects of the main variables (temperature, length of foliated season, CO2 fertilization, drought effect), show that the magnitude of these effects depends on the species and the climatic zone.
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
Evaluation of six process-based forest growth models using eddy-covariance measurements of CO2 and H2O fluxes at six forest sites in Europe
Kramer, K. ; Leinonen, I. ; Bartelink, H.H. ; Berbigier, P. ; Borghetti, M. ; Bernhofer, C. ; Cienciala, E. ; Dolman, H. ; Froer, O. ; Gracia, C.A. ; Granier, A. ; Grunwold, T. ; Hari, P. ; Jans, W.W.P. ; Kellomaki, S. ; Loustau, D. ; Magnani, F. ; Markkanen, T. ; Matteucci, G. ; Mohren, G.M.J. ; Moors, E.J. ; Nissinen, A. ; Peltola, H. ; Sabate, S. ; Sanchez, A. ; Sontag, M. ; Valentini, R. ; Vesala, T. - \ 2002
Global Change Biology 8 (2002)3. - ISSN 1354-1013 - p. 213 - 230.
mean squared error - ecosystem respiration - simulation-model - gas-exchange - net carbon - scots pine - water - atmosphere - productivity - constraints
Reliable models are required to assess the impacts of climate change on forest ecosystems. Precise and independent data are essential to assess this accuracy. The flux measurements collected by the EUROFLUX project over a wide range of forest types and climatic regions in Europe allow a critical testing of the process-based models which were developed in the LTEEF project. The ECOCRAFT project complements this with a wealth of independent plant physiological measurements. Thus, it was aimed in this study to test six process-based forest growth models against the flux measurements of six European forest types, taking advantage of a large database with plant physiological parameters. The reliability of both the flux data and parameter values itself was not under discussion in this study. The data provided by the researchers of the EUROFLUX sites, possibly with local corrections, were used with a minor gap-filling procedure to avoid the loss of many days with observations. The model performance is discussed based on their accuracy, generality and realism. Accuracy was evaluated based on the goodness-of-fit with observed values of daily net ecosystem exchange, gross primary production and ecosystem respiration (gC m2 d1), and transpiration (kg H2O m2 d1). Moreover, accuracy was also evaluated based on systematic and unsystematic errors. Generality was characterized by the applicability of the models to different European forest ecosystems. Reality was evaluated by comparing the modelled and observed responses of gross primary production, ecosystem respiration to radiation and temperature. The results indicated that: Accuracy. All models showed similar high correlation with the measured carbon flux data, and also low systematic and unsystematic prediction errors at one or more sites of flux measurements. The results were similar in the case of several models when the water fluxes were considered. Most models fulfilled the criteria of sufficient accuracy for the ability to predict the carbon and water exchange between forests and the atmosphere. Generality. Three models of six could be applied for both deciduous and coniferous forests. Furthermore, four models were applied both for boreal and temperate conditions. However, no severe water-limited conditions were encountered, and no year-to-year variability could be tested. Realism. Most models fulfil the criterion of realism that the relationships between the modelled phenomena (carbon and water exchange) and environment are described causally. Again several of the models were able to reproduce the responses of measurable variables such as gross primary production (GPP), ecosystem respiration and transpiration to environmental driving factors such as radiation and temperature. Stomatal conductance appears to be the most critical process causing differences in predicted fluxes of carbon and water between those models that accurately describe the annual totals of GPP, ecosystem respiration and transpiration. As a conclusion, several process-based models are available that produce accurate estimates of carbon and water fluxes at several forest sites of Europe. This considerable accuracy fulfils one requirement of models to be able to predict the impacts of climate change on the carbon balance of European forests. However, the generality of the models should be further evaluated by expanding the range of testing over both time and space. In addition, differences in behaviour between models at the process level indicate requirement of further model testing, with special emphasis on modelling stomatal conductance realistically
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