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

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). Highlights - ¿ A robust method is presented to quantify uncertainty of annual totals of net ecosystem productivity (NEP). ¿ The method contains uncertainty estimates for the most important known components of the total uncertainty: measurement error and flux calculation uncertainty, self-heating correction uncertainty, u* threshold uncertainty, statistical selection uncertainty and gap-filling uncertainty. ¿ The uncertainties associated with the friction velocity threshold criterion and measurement error and flux calculation are substantial and much higher than the other uncertainties. ¿ Total uncertainty of NEP for the Loobos site was on average ±32 g C m-2 a-1 (±8% of NEP). Abbreviations - NEP, annual net ecosystem productivity (g C m-2 a-1 positive values represent accumulation of carbon by the ecosystem); Fec, eddy-covariance flux (µmol m-2 s-1 positive values represent carbon released to the atmosphere); Fs, storage flux (µmol m-2 s-1 positive values represent carbon released to the atmosphere); NEE, net ecosystem exchange (µmol m-2 s-1 positive values represent carbon released to the atmosphere