Article

Assessing the uncertainty of estimated annual totals of net ecosystem productivity: A practical approach applied to a mid-latitude temperate pine forest

Alterra, Wageningen UR, Earth System Science and Climate Change Group, PO Box 47, 6700 AA, Wageningen, The Netherlands
Agricultural and Forest Meteorology (Impact Factor: 3.76). 07/2011; 151:1823-1830. DOI: 10.1016/j.agrformet.2011.07.020

ABSTRACT

Values for annual NEP of micrometeorological tower sites are usually published without an estimate of associated uncertainties. Few authors quantify total uncertainty of annual NEP. Moreover, different methods to assess total uncertainty are applied, usually addressing only one aspect of the uncertainty. This paper presents a robust and easy to apply method to quantify uncertainty of annual totals of Net Ecosystem Productivity (NEP), related to multiple factors involved therein. The method was applied to NEP observations for a Scots pine forest (Loobos) in the Netherlands. Total uncertainty of annual NEP for the Loobos site was on average ±32 g C m−2 a−1 (±8% of NEP), which is a quarter of the standard deviation of annual NEP (127 g C m−2 a−1).

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Available from: Jan A Elbers, Sep 03, 2014
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    • "The tower footprint stretches to several hundred metres, while the forest extends for more than 1.5 km in all directions from this point. EC data are processed to half-hourly corrected fluxes with the instrumentation and method described in Elbers et al. (2011). These data are quality checked, flagged and, if necessary, gap filled and split up in gross primary productivity (GPP) and ecosystem respiration (R eco ), using the online EC gap-filling and flux partitioning tool at http://www.bgc-jena.mpg.de/~MDIwork/ "
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    ABSTRACT: The vegetation–atmosphere carbon and water exchange at one particular site can strongly vary from year to year, and understanding this interannual variability in carbon and water exchange (IAVcw) is a critical factor in projecting future ecosystem changes. However, the mechanisms driving this IAVcw are not well understood. We used data on carbon and water fluxes from a multi-year eddy covariance study (1997–2009) in a Dutch Scots pine forest and forced a process-based ecosystem model (Lund–Potsdam–Jena General Ecosystem Simulator; LPJ-GUESS) with local data to, firstly, test whether the model can explain IAVcw and seasonal carbon and water exchange from direct environmental factors only. Initial model runs showed low correlations with estimated annual gross primary productivity (GPP) and annual actual evapotranspiration (AET), while monthly and daily fluxes showed high correlations. The model underestimated GPP and AET during winter and drought events. Secondly, we adapted the temperature inhibition function of photosynthesis to account for the observation that at this particular site, trees continue to assimilate at very low atmospheric temperatures (up to daily averages of −10 °C), resulting in a net carbon sink in winter. While we were able to improve daily and monthly simulations during winter by lowering the modelled minimum temperature threshold for photosynthesis, this did not increase explained IAVcw at the site. Thirdly, we implemented three alternative hypotheses concerning water uptake by plants in order to test which one best corresponds with the data. In particular, we analyse the effects during the 2003 heatwave. These simulations revealed a strong sensitivity of the modelled fluxes during dry and warm conditions, but no single formulation was consistently superior in reproducing the data for all timescales and the overall model–data match for IAVcw could not be improved. Most probably access to deep soil water leads to higher AET and GPP simulated during the heatwave of 2003. We conclude that photosynthesis at lower temperatures than assumed in most models can be important for winter carbon and water fluxes in pine forests. Furthermore, details of the model representations of water uptake, which are often overlooked, need further attention, and deep water access should be treated explicitly.
    Full-text · Article · Jul 2015 · Earth System Dynamics
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    • "Related literature (Stella et al., 2009) (Chiesi et al., 2005) (Suni et al., 2003) (Köster et al., 2013) (Nagy et al., 2006) (Elbers et al., 2011) (Lundin et al., 1999) (Ziemblińska et al., 2013) Localization (latitude/longitude, elevation): 1 – France 44°5'N 0°5'E, 60 m a.s.l.; 2 – Italy 43°43'N 10°17'E, 6 m a.s.l.; 3 , 4 – Finland 61°5'N 24°17'E, 170 m a.s.l.; 67°21'N 26°38'E, 180 m a.s.l.; 5 – Belgium 51°18'N 4°31'E, 16 m a.s.l.; 6 – Netherlands 2°10'N 5°44'E, 25 m a.s.l.; 7 – Sweden 60°5'N 17°29'E, 45 m a.s.l.; 8 – Poland 53°11'N 16°05'E, 180 m a.s.l. Excel (2007). "
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    ABSTRACT: The Scots pine is one of the most important species in European and Asian forests. Due to a widespread occurrence of pine forests, their significance in the energy and mass exchange between the Earth surface and the atmosphere is also important, particularly in the context of climate change and greenhouse gases balance. The aim of this work is to present the relationship between the average annual net ecosystem productivity and growing season length, latitude and air temperature (tay) over Europe. Therefore, CO
    Full-text · Article · Mar 2015 · International Agrophysics
    • "The tower footprint stretches to several hundred metres, while the forest extends for more than 1.5 km in all directions from this point. EC data are processed to half-hourly corrected fluxes with the instrumentation and method described in Elbers et al. (2011). These data are quality checked, flagged and, if necessary, gap filled and split up in gross primary productivity (GPP) and ecosystem respiration (R eco ), using the online EC gap-filling and flux partitioning tool at http://www.bgc-jena.mpg.de/~MDIwork/ "
    [Show abstract] [Hide abstract]
    ABSTRACT: Vegetation – atmosphere carbon and water exchange at one particular site can strongly vary from year to year, and understanding this interannual variability in carbon and water exchange (IAVcw) is a critical factor in projecting future ecosystem changes. However, the mechanisms driving this IAVcw are not well understood. We used data on carbon and water fluxes from a multi-year Eddy Covariance study (1997–2009) in a Dutch Scots pine forest and forced a process-based ecosystem model (LPJ-GUESS) with local data to, firstly, test whether the model can explain IAVcw and seasonal carbon and water exchange from direct environmental factors only. Initial model runs showed low correlations with estimated annual gross primary productivity (GPP) and annual actual evapotranspiration (AET), while monthly and daily fluxes showed high correlations. The model underestimated GPP and AET during winter and drought events. Secondly, we adapted the temperature inhibition function of photosynthesis to account for the observation that at this particular site, trees continue to assimilate at very low atmospheric temperatures (up to daily averages of −10 °C), resulting in a net carbon sink in winter. While we were able to improve daily and monthly simulations during winter by lowering the modelled minimum temperature threshold for photosynthesis, this did not increase explained IAVcw at the site. Thirdly, we implemented three alternative hypotheses concerning water uptake by plants in order to test which one best corresponds with the data. In particular, we analyse the effects during the 2003 heatwave. These simulations revealed a strong sensitivity of the modelled fluxes during dry and warm conditions, but no single formulation was consistently superior in reproducing the data for all time scales and the overall model-data match for IAVcw could not be improved. Most probably access to deep soil water leads to higher AET and GPP simulated during the heat wave of 2003. We conclude that photosynthesis at lower temperatures than assumed in most models can be important for winter carbon and water fluxes in pine forests. Furthermore, details of the model representations of water uptake, which are often overlooked, need further attention, and deep water access should be treated explicitly.
    No preview · Article · Feb 2015 · Earth System Dynamics Discussions 
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