## 2 Data and Methods  
### Data  
In this study, we used meteorological data and ecosystem fluxes measured with the eddy covariance (EC) technique at 58 sites pertaining to the FLUXNET network and the processed MODIS leaf area index (LAI) product (MOD15A2) to simulate GPP at half-hourly, daily and 8-day temporal scales. The meteorological and flux data belongs to the LaThuile FLUXNET dataset and can be freely downloaded [35]. The sites were selected on the basis of the availability of key datasets, such as LAI, meteorology, and land surface C fluxes. GPP derived from tower measured NEP was used as benchmarks for model parameter optimization and model evaluation. All flux data were processed in the manner proposed within the Fluxnet project [36, 37] as described by [38, 39, 40, 41]. The 58 sites included 21 needle-leaf-forest (NF) sites, with 1 deciduous needle-leaf-forest (DNF) sites and 20 evergreen needle-leaf-forest (ENF) sites, 11 broadleaf-forest (BF) sites, with 2 evergreen broadleaf-forest (EBF) sites and 9 deciduous broadleaf-forest (DBF) sites, 4 mixed-forest (MF) sites, 7 crop (CROP) sites, 7 grassland (GRASS) sites, and 8 shrub (SHRUB) sites, located in Asia, Europe, and North America (Figure 1). The observations covered the period from January 2001 to December 2007 with at least two years of data for each site. In total, 143 site-years of data were used, of which 85 site-years of data were selected for parameter optimization (17 BF, 11 CROP, 10 GRASS, 6 MF, 29 NF, and 12 SHRUB site-years). The remaining 58 site-years of data were used for model evaluation, with one year of data for each site. Detailed information about each site is given in Table 1.  
Figure 1: Distribution of all sites with data used for parameter optimization and validation in this study. The background is the MODIS global land cover product (MCD12C1) in 2003. \begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Site Name** & **Country** & **Lat. (\({}^{\circ}\))** & **Long. (\({}^{\circ}\))** & **Veg.** & **Opti.** & **Vali.** & **Reference** \\  & & & & **Type** & **Years** & **Years** & \\ \hline Austin Cary (ACA) & USA & 29.74 & \(-\)82.22 & NF & 2003 & 2005 & Gholz and Clark (2002) [42] \\ ARM\_SGP\_Main (ASM) & USA & 36.61 & \(-\)97.49 & CROP & 2003 & 2004 & [PERSON] _et al._ (2007) [43] \\ Audubon (AUD) & USA & 31.59 & \(-\)110.51 & GRASS & 2003 & 2004 & [PERSON] and Meyers (2007) [44] \\ BC-DFir1949 (BD49) & Canada & 49.87 & \(-\)125.33 & NF & 2003 & 2004 & [PERSON] _et al._ (2006) [45] \\ Bartlett Experimental (BEP) & USA & 44.06 & \(-\)71.29 & BF & 2005 & 2006 & [PERSON] _et al._ (2007) [46] \\ BC-Harvest Dfr2000 (DF00) & Canada & 49.87 & \(-\)125.29 & NF & 2003 & 2004 & [PERSON] _et al._ (2006) [45] \\ BC-Harvest Dir1988 (DF88) & Canada & 49.53 & \(-\)124.9 & NF & 2004 & 2005 & [PERSON] _et al._ (2006) [45] \\ [PERSON] (BON) & USA & 40.01 & \(-\)88.29 & CROP & 2004,2005 & 2006 & [PERSON] and Meyers (2007) [44] \\ [PERSON] (CBS) & China & 42.40 & 128.10 & MF & 2003 & 2004 & [PERSON] _et al._ (2006a,b) [47,48] \\ [PERSON](DHS) & China & 23.17 & 112.53 & BF & 2003 & 2004 & [PERSON] _et al._ (2000) [49] \\ [PERSON] (DON) & USA & 29.75 & \(-\)82.16 & NF & 2003 & 2004 & Gholz and Clark (2002) [42] \\ El Saler (ES) & Spain & 39.35 & \(-\)0.32 & NF & 2001,2002 & 2003 & [PERSON] _et al._ (2006) [50] \\ Fort Peck (FPE) & USA & 48.31 & \(-\)105.1 & GRASS & 2003 & 2004 & [PERSON] and Meyers (2007) [44] \\ [PERSON] (FY) & Russia & 56.46 & 32.92 & NF & 2001 & 2003 & [PERSON] _et al._ (2002) [51] \\ Goodwin Creek (GCR) & USA & 34.25 & \(-\)89.87 & GRASS & 2004,2005 & 2006 & [PERSON] and Meyers (2007) [44] \\ Hainich (HA) & Germany & 51.08 & 10.45 & BF & 2001,2002 & 2003 & [PERSON] _et al._ (2010) [52] \\ Harvard Forest (HAF) & USA & 42.54 & \(-\)72.17 & BF & 2005 & 2006 & [PERSON] _et al._ (2007) [53] \\ [PERSON] (HB) & China & 37.67 & 101.33 & GRASS & 2003 & 2004 & [PERSON] _et al._ (2013) [23] \\ [PERSON] (HES) & France & 48.67 & 7.07 & BF & 2001,2002 & 2003 & [PERSON] _et al._ (2002) [54] \\ \hline \hline \end{tabular}
\end{table}