E. Falge

Max Planck Institute for Biogeochemistry Jena, Jena, Thuringia, Germany

Are you E. Falge?

Claim your profile

Publications (90)141.35 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments coupling changes of surface properties and processes with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan plateau. We coupled measurements of micro-lysimeter, chamber, 13C labeling, and eddy-covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyze how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation
    Biogeosciences Discussions 06/2014; 11:8861-8923.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments investigating changes of surface properties and processes together with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan Plateau. We connected measurements of micro-lysimeter, chamber, 13C labelling, and eddy covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyse how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum of evapotranspiration over a longer period cannot be confirmed. The results show an earlier onset of convection and cloud generation, likely triggered by a shift in evapotranspiration timing when dominated by evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a significant influence on larger scales.
    Biogeosciences 01/2014; 11:6633-6656. · 3.75 Impact Factor
  • Source
    28th Himalayan Karakorum Tibet Workshop and 6th International Symposium on Tibetan Plateau Joint Conference, Tuebingen; 08/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: Since about two decades, fast response ozone analyzers, based on gas-phase chemiluminescence ("Güsten type"), became more and more available and emerged to be operational in atmosphere-biosphere exchange studies using the eddy-covariance technique. While there are first preliminary reports about measurements of the vertical profile of ozone fluxes in forest canopies (addressing the question of vertical flux divergence), measurements by ozone flux stations distributed in a horizontally arranged array (addressing questions of horizontal divergence and/or footprint) might be feasible. For all these measurements, the precision of ozone flux stations is of particular interest, because it defines the vertical/horizontal resolution of expected flux divergence. As a first step in this direction, we performed a 9 week, side-by-side experiment of three ozone flux stations on a small airfield in Mainz-Finthen/Germany (49.969° N, 8.148° E, 227 m a.s.l.) in late summer/autumn 2011. Turbulent fluctuations of ozone concentration (in arbitrary units) have been measured by three identical gas-phase chemiluminescence anaylzers (enviscope GmbH/ Germany) with a sampling frequency of 20 Hz. Absolute ozone concentrations have been monitored by three slow-response UV-absorption based analyzers (model 205, 2BTechnologies/U.S.A.; model 49i, ThermoInstruments/U.S.A.) every 2 and 10 seconds, respectively. Three 3D sonic anemometers (model USA-1, METEK/Germany; model CSAT3, Campbell Scientific/U.K.) have been applied to obtain fluctuations of 3D wind vectors and temperature (20Hz). All fast response sensors were mounted at 3 m above ground, the three flux stations have been aligned in cross-wind direction in a distance of about 5.5 m to each other. Sensor separation (3D anemometer - ozone intake) was 0.3 m, the length of ozone intake tubes were about 3 m. Ozone monitors have routinely been calibrated every 15 days. For the calculation of turbulent fluxes of ozone, momentum, and sensible heat from the observed time series we used the well-known TK3 algorithm (Department of Micrometeorology, University Bayreuth, Germany), particularly to provide TK3's quality assurance and quality control (QA/QC) measures. We will present results of different sensor combinations to elucidate the impact of instrumental variability (among fast-response and slow-response ozone analyzers, as well as among 3D ultrasonic anemometers) on the evaluation of the ozone flux. Finally, we will quantify the precision of ozone flux stations under field conditions.
    04/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: As part of the EGER (ExchanGE processes in mountainous Regions) project the exchange of ozone between the atmosphere and a forest / clear-cut was investigated during summer 2011 in the Fichtelgebirge mountains (SE Germany). The winter storm "Kyrill" (2007) generated a road-like wind-throw in the spruce-forest ecosystem "Weidenbrunnen". The wind-throw was cleared from stems and trees and until 2010 secondary vegetation developed, which consists mainly of young Spruce, Calamagrostis, Deschampsia and Vaccinium and differs in its phenology and leaf physiology from the original Picea abies. We seized the opportunity to investigate (a) differences of the ozone exchange between the spruce forest and the clear-cut vegetation, and (b) the influence of the disturbed ecosystem as a whole on the exchange. Several towers were installed within the forest, in the clear-cut, and along the forest/clear-cut edge. The eddy-covariance technique was applied to measure vertical turbulent fluxes of ozone. Two fast (20 Hz) gas-phase chemiluminescence ozone analyzers (enviscope GmbH) were used to measure the turbulent fluctuations of ozone mixing ratio in arbitrary units, while the absolute ozone mixing ratio was monitored by slow-response (0.5 Hz), UV-absorption based ozone analyzers (2BTechnologies). Fast and slow-response measurements of ozone mixing ratio were performed at 32 m above the forest floor and 5.5 m above the soil surface in the clear-cut. In both cases, the fast ozone analyzers were combined with 3D sonic anemometers (METEK USA-1, Campbell CSAT3) For the calculation of turbulent fluxes of ozone, momentum, and sensible heat from the observed time series a computer based algorithm was applied that was developed in the EGER program previously. Dry deposition velocities of ozone were also determined. In addition to our flux calculating procedure, fluxes were also calculated by the well-known TK3 algorithm (Department of Micrometeorology, University Bayreuth, Germany) to check for consistency and to provide TK3's quality assurance and quality control (QA/QC) measures. The ozone flux differences between forest and clear cut are analyzed for mean daily cycles averaged over the whole measuring period as well as for three periods of four to five days with fairly good conditions. While the averaged flux above the forest show a clear diel variation with nighttime fluxes between -0.3 and -0.4 μg m-2 s-1 and daytime fluxes up to -0.6 μg m-2 s-1, the flux in the clear-cut shows nearly no diel cycle and is about one order of magnitude smaller than above the forest.
    04/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the energy, matter and reactive and non-reactive trace gas exchange between the atmosphere and a spruce forest in the German mountain region, two inten-sive measuring periods were conducted at the FLUXNET site DE-Bay (Waldstein-Weidenbrunnen) in September/October 2007 and June/July 2008. They were part of the project "Ex-chanGE processes in mountainous Regions" (EGER). Be-yond a brief description of the experiment, the main focus of the paper concerns the coupling between the trunk space, the canopy and the above-canopy atmosphere. Therefore, relevant coherent structures were analyzed for different in-and above canopy layers, coupling between layers was classi-fied according to already published procedures, and gradients and fluxes of meteorological quantities as well as concen-trations of non-reactive and reactive trace compounds have been sorted along the coupling classes. Only in the case of a fully coupled system, it could be shown, that fluxes measured above the canopy are related to gradients between the canopy and the above-canopy atmosphere. Temporal changes of con-centration differences between top of canopy and the forest floor, particularly those of reactive trace gases (NO, NO 2 , O 3 , and HONO) could only be interpreted on the basis of the coupling stage. Consequently, only concurrent and verti-cally resolved measurements of micrometeorological (turbu-lence) quantities and fluxes (gradients) of trace compounds will lead to a better understanding of the forest-atmosphere interaction.
    Atmospheric Chemistry and Physics 01/2012; 12:1923--1950. · 5.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: {textlessptextgreatertextless}br/textgreaterThe components of ecosystem evapotranspiration of a Norway spruce forest (Picea abies L.) as well as the vertical structure of canopy evapotranspiration were analyzed with a combination of measurements and models for a case study of 5 days in September 2007. Eddy-covariance and sap flux measurements were performed at several heights within the canopy at the FLUXNET site Waldstein-Weidenbrunnen (DE-Bay) in the Fichtelgebirge mountains in Germany. Within and above canopy fluxes were simulated with two stand-scale models, the 1D multilayer model ACASA that includes a third-order turbulence closure and the 3D model STANDFLUX. The soil and understory evapotranspiration captured with the eddy-covariance system in the trunk space constituted 10% of ecosystem evapotranspiration measured with the eddy-covariance system above the canopy. A comparison of transpiration measured with the sap flux technique and inferred from below and above canopy eddy-covariance systems revealed higher estimates from eddy-covariance measurements than for sap flux measurements. The relative influences of possible sources of this mismatch, such as the assumption of negligible contribution of evaporation from intercepted water, and differences between the eddy-covariance flux footprint and the area used for scaling sap flux measurements, were discussed. Ecosystem evapotranspiration as well as canopy transpiration simulated with the two models captured the dynamics of the measurements well, but slightly underestimated eddy-covariance values. Profile measurements and models also gave us the chance to assess in-canopy profiles of canopy evapotranspiration and the contributions of in-canopy layers. For daytime and a coupled or partly coupled canopy, mean simulated profiles of both models agreed well with eddy-covariance measurements, with a similar performance of the ACASA and the STANDFLUX model. Both models underestimated profiles for nighttime and decoupled conditions. During daytime, the upper half of the canopy contributed approximately 80% to canopy evapotranspiration, whereas during nighttime the contribution shifted to lower parts of the canopy.textless/ptextgreater
    Agricultural and Forest Meteorology. 01/2011; 151(6):709-729.
  • Source
    Atmospheric Chemistry and Physics Discussions. 01/2011; 11(9):26245-26345.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The process-based spatial simulation model SVAT-CN was used to estimate biogenic nitric oxide (NO) emission by soils of a Norway spruce forest (Weidenbrunnen) in the Fichtelgebirge, Germany. SVAT-CN core is a combination of a multiple-layer soil water balance model and a multi-layered canopy gas exchange model. The soil modules comprise a flexible hybrid between a layered bucket model and classical basic liquid flow theory. Further soil processes include: heat transport, distribution of transpiration demand proportionally to soil resistance, reduction of leaf physiological parameters with limiting soil moisture. Spruce forest soils usually are characterized by a thick organic layer (raw humus), with the topmost centimetres being the location where most of the biogenic NO is produced. Within individual spruce forest stands the understory might be composed of patches characterized by different species (e.g. Vaccinium myrtillus, Picea abies, Deschampsia caespitosa), and NO production potentials. The effect of soil physical and chemical parameters and understory types on NO emission from the organic layer was investigated in laboratory incubation and fumigation experiments on soils sampled below the various understory covers found at the Weidenbrunnen site. Results from the laboratory experiments were used to parameterize multi-factorial regression models of soil NO emission with respect to its response to soil temperature and moisture. Parameterization of the spatial model SVAT-CN includes horizontal heterogeneity of over- and understory PAI, understory species distribution, soil texture, bulk density, thickness of organic layer. Simulations are run for intensive observations periods of 2007 and 2008 of the EGER (ExchanGE processes in mountainous Regions) project, a late summer/fall and an early summer period, providing estimates for different understory types (young spruce, blueberry, grass, and moss/litter patches). Validation of the model is being carried out at point scale, by comparison with measured soil moisture and temperature data at 12 locations at the Weidenbrunnen site. In addition model output is compared to soil NO emission data from dynamic chambers. Understory type was found to have a strong influence on the magnitude of soil NO emissions, with emissions from blueberry and young spruce one order of magnitude larger than those from grass or moss/litter patches.
    05/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nitric oxide (NO) plays an important role in the photochemistry of the troposphere. NO from soil contributes up to 40% to the global budget of atmospheric NO. Soil NO emissions are primarily caused by biological activity (nitrification and denitrification), that occurs in the uppermost centimeter of the soil, a soil region often characterized by high contents of organic material. Most studies of NO emission potentials to date have investigated mineral soil layers. In our study we sampled soil organic matter under different understories (moss, grass, spruce and blueberries) in a humid mountainous Norway spruce forest plantation in the Fichtelgebirge (Germany). We performed laboratory incubation and flushing experiments using a customized chamber technique to determine the response of net potential NO flux to physical and chemical soil conditions (water content and temperature, bulk density, particle density, pH, C/N ratio, organic C, soil ammonium, soil nitrate). Net potential NO fluxes (in terms of mass of N) from soil samples taken under different understories ranged from 1.7-9.8 ng m-2 s-1 (soil sampled under grass and moss cover), 55.4-59.3 ng m-2 s-1 (soil sampled under spruce cover), and 43.7-114.6 ng m-2 s-1 (soil sampled under blueberry cover) at optimum water content and a soil temperature of 10 °C. The water content for optimum net potential NO flux ranged between 0.76 and 0.8 gravimetric soil moisture for moss covered soils, between 1.0 and 1.1 for grass covered soils, 1.1 and 1.2 for spruce covered soils, and 1.3 and 1.9 for blueberry covered soils. Effects of soil physical and chemical characteristics on net potential NO flux were statistically significant (0.01 probability level) only for NH4+. Therefore, as an alternative explanation for the differences in soil biogenic NO emission we consider more biological factors like understory vegetation type, amount of roots, and degree of mycorrhization; they have the potential to explain the observed differences of net potential NO fluxes.
    Biogeosciences 05/2010; · 3.75 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nitric oxide (NO) plays an important role in the photochemistry of the troposphere. NO from soil contributes up to 40% to the global budget of atmospheric NO. Soil NO emissions are primarily caused by biological activity (nitrification and denitrification), that occurs in the uppermost centimetres of the soil, a soil region often characterized by high contents of organic material. Most studies of NO emission potentials to date have investigated mineral soil layers. In our study we sampled soil organic matter under different understories (moss, grass, spruce and blueberries) in a humid mountainous Norway spruce forest plantation in the Fichtelgebirge (Germany). We performed laboratory incubation and fumigation experiments using a customized chamber technique to determine the response of net potential NO flux to physical and chemical soil conditions (water content and temperature, bulk density, particle density, pH, C/N ratio, organic C, soil ammonium, soil nitrate). Net potential NO fluxes (in terms of mass of N) from soils of different understories ranged from 1.7–9.8 ng m−2 s−1 (grass and moss), 55.4–59.3 ng m−2 s−1 (spruce), and 43.7–114.6 ng m−2 s−1 (blueberry) at optimum water content and a soil temperature of 10°C. The water content for optimum net potential NO flux ranged between 0.76 and 0.8 gravimetric soil moisture for moss, between 1.0 and 1.1 for grass, 1.1 and 1.2 for spruce, and 1.3 and 1.9 for blueberries. Effects of soil physical and chemical characteristics on net potential NO flux were statistically significant (0.01 probability level) only for NH4+. Therefore, the effects of biogenic factors like understory type, amount of roots, and degree of mycorrhization on soil biogenic NO emission are discussed; they have the potential to explain the observed different of net potential NO fluxes. Quantification of NO emissions from the upmost soil layer is therefore an important step to quantify soil NO emissions in ecosystems with substantial organic soil horizons.
    Biogeosciences Discussions. 01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The sensitivity and predictive uncertainty of the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) was assessed by employing the Generalized Likelihood Uncertainty Estimation (GLUE) method. ACASA is a stand-scale, multi-layer soil-vegetation-atmosphere transfer model that incorporates a third order closure method to simulate the turbulent exchange of energy and matter within and above the canopy. Fluxes simulated by the model were compared to sensible and latent heat fluxes as well as the net ecosystem exchange measured by an eddy-covariance system above the spruce canopy at the FLUXNET-station Waldstein-Weidenbrunnen in the Fichtelgebirge Mountains in Germany. From each of the intensive observation periods carried out within the EGER project (ExchanGE processes in mountainous Regions) in autumn 2007 and summer 2008, five days of flux measurements were selected. A large number (20 000) of model runs using randomly generated parameter sets were performed and goodness of fit measures for all fluxes for each of these runs calculated. The 10% best model runs for each flux were used for further investigation of the sensitivity of the fluxes to parameter values and to calculate uncertainty bounds. A strong sensitivity of the individual fluxes to a few parameters was observed, such as the leaf area index. However, the sensitivity analysis also revealed the equifinality of many parameters in the ACASA model for the investigated periods. The analysis of two time periods, each representing different meteorological conditions, provided an insight into the seasonal variation of parameter sensitivity. The calculated uncertainty bounds demonstrated that all fluxes were well reproduced by the ACASA model. In general, uncertainty bounds encompass measured values better when these are conditioned on the respective individual flux only and not on all three fluxes concurrently. Structural weaknesses of the ACASA model concerning the soil respiration calculations were detected and improvements suggested.
    Biogeosciences 01/2010; · 3.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) was used to model the turbulent fluxes of heat, water vapor and momentum as well as the carbon dioxide exchange within and above a spruce canopy at the FLUXNET-station Waldstein-Weidenbrunnen (DE-Bay) in the Fichtelgebirge mountains in northern Bavaria, Germany. ACASA is a multilayer canopy-surface-layer model that incorporates a third-order closure method to calculate turbulent transfer within and above the canopy and was developed at the University of California, Davis. Within the EGER (ExchanGE processes in mountainous Regions) project, comprehensive micrometeorological and plant physiological measurements were performed during two intensive observation periods in fall 2007 and summer 2008. This data base allowed us to extensively test the ability of the ACASA model to simulate the exchange of energy and matter at our site. Here, the vertical structure of evapotranspiration within and above the canopy for a few days is investigated in detail. The ACASA model provides profiles of all components of evapotranspiration, such as transpiration and evaporation from the soil, and estimates the interception of precipitation and the corresponding evaporation from wet plant surfaces. Fluxes of momentum, heat, carbon dioxide and water vapor were measured with six eddy-covariance systems below, within and above the canopy on a 36 m high tower. Furthermore, xylem sapflow measurements at six heights within the canopy were performed for the determination of canopy transpiration. This combination of multilevel measurements allowed us to estimate all components of evapotranspiration of and within the spruce forest. Model results and measurements of evapotranspiration are analyzed with regard to the partitioning between its components as well as between the canopy layers. Furthermore, the ability of the ACASA model to reproduce evapotranspiration profiles for different exchange regimes of the subcanopy and the canopy is assessed.
    AGU Fall Meeting Abstracts. 12/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the interactive effects of canopy structural and optical properties on vegetation/atmosphere exchange, validated models are necessary that allow for canopy heterogeneity in structure and physiological traits. We used a three dimensional (3D) canopy light absorptance model (STANDFLUX, Ryel et al. 1993, Falge et al. 1997) to illustrate how reflection and transmission properties of needles interact with canopy structure and produce probability density functions (PDFs) for light transmittance, transpiration, and net photosynthesis in horizontal canopy layers of the Weidenbrunnen site, a 54-year-old Picea abies (L.) Karst. stand. The stand is located in the Lehstenbach catchment, a subcatchment of the Eger catchment. Model parameterization was obtained for the intensive campaigns of the EGER project in fall 2007 and early summer 2008. Simulation results for the biosphere exchange of latent heat in the horizontal canopy layers were compared with analogous PDFs of latent heat fluxes as measured by eddy covariance above and below the canopy, yet limited by the ergodic assumption during the assimilation of eddy covariance data (time for space substitution). Comparisons of the model results with eddy covariance estimates for latent heat exchange are analyzed with respect to coupling stages of the subcanopy and canopy of this managed montane forest. 3D distribution of tree biomass are key for defining surfaces for source or sink strength of (trace) gases, and 3D irregularities in the canopy are crucial for defining potential flow paths for advection processes within the canopy. For the future, airborne photographs or remote sensing scenes for the Lehstenbach catchment must be evaluated together with extended model simulations to determine the spatial variability of biosphere gas exchange. The results are a contribution to the EGER project (Exchange Processes in Mountainous Regions, Deutsche Forschungsgemeinschaft), which investigates the role of process interactions among different scales of soil, in-canopy and atmospheric processes for mass and energy budgets of vegetated surfaces.
    04/2009;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Eddy covariance flux towers measure net exchange of land–atmosphere flux. For the flux of carbon dioxide, this net ecosystem exchange (NEE) is governed by two processes, gross primary production (GPP) and a sum of autotrophic and heterotrophic respiration components known as ecosystem respiration (RE). A number of statistical flux-partitioning methods, often developed to fill missing NEE data, can also be used to estimate GPP and RE from NEE time series. Here we present results of the first comprehensive, multi-site comparison of these partitioning methods. An initial test was performed with a subset of methods in retrieving GPP and RE from NEE generated by an ecosystem model, which was also degraded with realistic noise. All methods produced GPP and RE estimates that were highly correlated with the synthetic data at the daily and annual timescales, but most were biased low, including a parameter inversion of the original model. We then applied 23 different methods to 10 site years of temperate forest flux data, including 10 different artificial gap scenarios (10% removal of observations), in order to investigate the effects of partitioning method choice, data gaps, and intersite variability on estimated GPP and RE. Most methods differed by less than 10% in estimates of both GPP and RE. Gaps added an additional 6–7% variability, but did not result in additional bias. ANOVA showed that most methods were consistent in identifying differences in GPP and RE across sites, leading to increased confidence in previously published multi-site comparisons and syntheses. Several methods produced outliers at some sites, and some methods were systematically biased against the ensemble mean. Larger model spread was found for Mediterranean sites compared to temperate or boreal sites. For both real and synthetic data, high variability was found in modeling of the diurnal RE cycle, suggesting that additional study of diurnal RE mechanisms could help to improve partitioning algorithms.
    Agricultural and Forest Meteorology 06/2008; 148:821-838. · 3.89 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Information about the uncertainties associated with eddy covariance measurements of surface–atmosphere CO2 exchange is needed for data assimilation and inverse analyses to estimate model parameters, validation of ecosystem models against flux data, as well as multi-site synthesis activities (e.g., regional to continental integration) and policy decision-making. While model residuals (mismatch between fitted model predictions and measured fluxes) can potentially be analyzed to infer data uncertainties, the resulting uncertainty estimates may be sensitive to the particular model chosen. Here we use 10 site-years of data from the CarboEurope program, and compare the statistical properties of the inferred random flux measurement error calculated first using residuals from five different models, and secondly using paired observations made under similar environmental conditions. Spectral analysis of the model predictions indicated greater persistence (i.e., autocorrelation or “memory”) compared to the measured values. Model residuals exhibited weaker temporal correlation, but were not uncorrelated white noise. Random flux measurement uncertainty, expressed as a standard deviation, was found to vary predictably in relation to the expected magnitude of the flux, in a manner that was nearly identical (for negative, but not positive, fluxes) to that reported previously for forested sites. Uncertainty estimates were generally comparable whether the uncertainty was inferred from model residuals or paired observations, although the latter approach resulted in somewhat smaller estimates. Higher order moments (e.g., skewness and kurtosis) suggested that for fluxes close to zero, the measurement error is commonly skewed and leptokurtic. Skewness could not be evaluated using the paired observation approach, because differencing of paired measurements resulted in a symmetric distribution of the inferred error. Patterns were robust and not especially sensitive to the model used, although more flexible models, which did not impose a particular functional form on relationships between environmental drivers and modeled fluxes, appeared to give the best results. We conclude that evaluation of flux measurement errors from model residuals is a viable alternative to the standard paired observation approach.
    Agricultural and Forest Meteorology 01/2008; · 3.89 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Global Change Biology 03/2007; 13(4):734 - 760. · 8.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Flux measurements from eight global FLUXNET sites were used to estimate parameters in a process-based, land-surface model (CSIRO Biosphere Model (CBM), using nonlinear parameter estimation techniques. The parameters examined were the maximum photosynthetic carboxylation rate () the potential photosynthetic electron transport rate (jmax, 25) of the leaf at the top of the canopy, and basal soil respiration (rs, 25), all at a reference temperature of 25°C. Eddy covariance measurements used in the analysis were from four evergreen forests, three deciduous forests and an oak-grass savanna. Optimal estimates of model parameters were obtained by minimizing the weighted differences between the observed and predicted flux densities of latent heat, sensible heat and net ecosystem CO2 exchange for each year. Values of maximum carboxylation rates obtained from the flux measurements were in good agreement with independent estimates from leaf gas exchange measurements at all evergreen forest sites. A seasonally varying and jmax, 25 in CBM yielded better predictions of net ecosystem CO2 exchange than a constant and jmax, 25 for all three deciduous forests and one savanna site. Differences in the seasonal variation of and jmax, 25 among the three deciduous forests are related to leaf phenology. At the tree-grass savanna site, seasonal variation of and jmax, 25 was affected by interactions between soil water and temperature, resulting in and jmax, 25 reaching maximal values before the onset of summer drought at canopy scale. Optimizing the photosynthetic parameters in the model allowed CBM to predict quite well the fluxes of water vapor and CO2 but sensible heat fluxes were systematically underestimated by up to 75 W m−2.
    Global Change Biology 03/2007; 13(3):652-670. · 8.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Agricultural and Forest Meteorology. 01/2007; 143(1-2):123-145.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We review 15 techniques for estimating missing values of net ecosystem CO2 exchange (NEE) in eddy covariance time series and evaluate their performance for different artificial gap scenarios based on a set of 10 benchmark datasets from six forested sites in Europe.
    Agricultural and Forest Meteorology. 01/2007; 147(3-4):209-232.

Publication Stats

6k Citations
141.35 Total Impact Points

Institutions

  • 2010
    • Max Planck Institute for Biogeochemistry Jena
      Jena, Thuringia, Germany
  • 2008
    • Max Planck Institute for Chemistry
      Mayence, Rheinland-Pfalz, Germany
  • 1996–2007
    • University of Bayreuth
      • Chair of Plant Ecology
      Bayreuth, Bavaria, Germany
  • 2000–2001
    • University of California, Berkeley
      • Division of Ecosystem Sciences
      Berkeley, California, United States