Using FLUXNET data to improve models of springtime vegetation activity onset in forest ecosystems
Melaas, E. ; Richardson, A. ; Friedl, M. ; Dragoni, D. ; Gough, C. ; Herbst, M. ; Montagnani, L. ; Moors, E.J. - \ 2013
Agricultural and Forest Meteorology 171-172 (2013). - ISSN 0168-1923 - p. 46 - 56.
terrestrial biosphere model - deciduous forest - co2 exchange - temperate regions - soil-temperature - phenology model - carbon-dioxide - annual cycle - bud-burst - trees
Vegetation phenology is sensitive to climate change and variability, and is a first order control on the carbon budget of forest ecosystems. Robust representation of phenology is therefore needed to support model-based projections of how climate change will affect ecosystem function. A variety of models have been developed to predict species or site-specific phenology of trees. However, extension of these models to other sites or species has proven difficult. Using meteorological and eddy covariance data for 29 forest sites (encompassing 173 site-years), we evaluated the accuracy with which 11 different models were able to simulate, as a function of air temperature and photoperiod, spatial and temporal variability in the onset of spring photosynthetic activity. In parallel, we also evaluated the accuracy with which dynamics in remotely sensed vegetation indices from MODIS captured the timing of spring onset. To do this, we used a subset of sites in the FLUXNET La Thuile database located in evergreen needleleaf and deciduous broadleaf forests with distinct active and dormant seasons and where temperature is the primary driver of seasonality. As part of this analysis we evaluated predictions from refined versions of the 11 original models that include parameterizations for geographic variation in both thermal and photoperiod constraints on phenology. Results from cross-validation analysis show that the refined models predict the onset of spring photosynthetic activity with significantly higher accuracy than the original models. Estimates for the timing of spring onset from MODIS were highly correlated with the onset of photosynthesis derived from flux measurements, but were biased late for needleleaf sites. Our results demonstrate that simple phenology models can be used to predict the timing of spring photosynthetic onset both across sites and across years at individual sites. By extension, these models provide an improved basis for predicting how the phenology and carbon budgets of temperature-limited forest ecosystems may change in the coming decades.
Thermal adaptation of net ecosystem exchange
Yuan, W. ; Luo, Y. ; Liang, S. ; YU, G. ; Niu, S. ; Stoy, J. ; Chen, J. ; Desai, A.R. ; Lindroth, A. ; Gough, C.M. ; Ceulenmans, R. ; Arain, A. ; Bernhofer, C. ; Cook, B. ; Cook, D.R. ; Dragoni, D. ; Gielen, B. ; Janssens, I.A. ; Longdoz, B. ; Liu, H. ; Lund, M. ; Matteucci, G. ; Moors, E.J. ; Scott, R.L. ; Seufert, G. ; Varner, R. - \ 2011
Biogeosciences 8 (2011)6. - ISSN 1726-4170 - p. 1453 - 1463.
carbon-dioxide exchange - long-term measurements - oak-dominated forest - scots pine forest - sub-alpine forest - soil respiration - deciduous forest - interannual variability - temperate forest - european forests
Thermal adaptation of gross primary production and ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of net ecosystem exchange of carbon (NEE). In this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland ecosystems located at latitudes ranging from ~29° N to 64° N. The response curves were used to define two critical temperatures: transition temperature (Tb) at which ecosystem transfer from carbon source to sink and optimal temperature (To) at which carbon uptake is maximized. Tb was strongly correlated with annual mean air temperature. To was strongly correlated with mean temperature during the net carbon uptake period across the study ecosystems. Our results imply that the net ecosystem exchange of carbon adapts to the temperature across the geographical range due to intrinsic connections between vegetation primary production and ecosystem respiration.
Latitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables
Yuan, W.P. ; Luo, Y.Q. ; Richardson, A.D. ; Oren, R. ; Luyssaert, S. ; Janssens, I.A. ; Ceulemans, R. ; Zhou, X.H. ; Grunwald, T. ; Aubinet, M. ; Berhofer, C. ; Baldocchi, D.D. ; Chen, J.Q. ; Dunn, A.L. ; Deforest, J.L. ; Dragoni, D. ; Goldstein, A.H. ; Moors, E.J. ; Munger, J.W. ; Monson, R.K. ; Suyker, A.E. ; Star, G. ; Scott, R.L. ; Tenhunen, J. ; Verma, S.B. ; Vesala, T. ; Wofsy, S. - \ 2009
Global Change Biology 15 (2009)12. - ISSN 1354-1013 - p. 2905 - 2920.
netto ecosysteem uitwisseling - kooldioxide - eddy-covariantie - patronen - ruimtelijke variatie - variatie in de tijd - net ecosystem exchange - carbon dioxide - eddy covariance - patterns - spatial variation - temporal variation - water-vapor exchange - northern temperate grassland - native tallgrass prairie - carbon-dioxide exchange - long-term measurements - plant functional-type - eddy covariance data - deciduous forest - european forests - co2 exchange
Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in net ecosystem exchange (NEE) of CO2 based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from ~29°N to ~64°N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.
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
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.