## 3 Results
### Spatial Distribution of Global VPP Estimates  
We investigated the spatial distribution of the global averaged SOG and EOG estimates for the period 2001-2017 (Figure 5a,b, respectively) as well as changes in SOG and EOG along with latitude (Figure 5c,d, respectively). Generally, the SOG decreases with a decrease in latitude, ranging from DOY 165 to DOY 80 between 85\({}^{\circ}\)N and 17\({}^{\circ}\)N, while it increases from DOY 80 to DOY 120 between 17\({}^{\circ}\)N and 13\({}^{\circ}\)N due to the arid climate of North Africa. Thereafter, it sharply decreases again from DOY 120 to DOY 65 between 13\({}^{\circ}\)N and the equator. In the Southern hemisphere, the SOG increases from DOY 250 at the equator to DOY 300 at 18\({}^{\circ}\)S, decreases from DOY 300 at 18\({}^{\circ}\)S to DOY 250 at 38\({}^{\circ}\)S, and then fluctuates between DOY 250 and DOY 300. The EOG increases with a decrease in latitude, ranging from DOY 235 at 85\({}^{\circ}\)N to DOY 305 at the equator. The EOG increases from DOY 130 at the equator to DOY 160 at 15\({}^{\circ}\)S, decreases to DOY 120 at 30\({}^{\circ}\)S, and then remains relatively stable from 30\({}^{\circ}\)S to 55\({}^{\circ}\)S in the Southern hemisphere.  
In the Northern hemisphere, late SOG occurs at high latitudes in the mid-western United States of America, the Alps in Europe, northeast and western China, central India, and North Africa, with SOG values ranging between DOY 130 and 180. In the Southern hemisphere, late SOG occurs in northern Australia, South Africa, and southern South America, with SOG values ranging between DOY 300 and 330. Early SOG is observed in the southeastern regions of the United States of America, across the Amazon, Western Europe, Central Africa, Southeast China, and Asia. Early EOG, with values ranging from DOY 240 to DOY 280, was found at high latitudes in the mid-western United States of America, Western Europe, North China, and western India. The spatial variation in EOG in the Southern hemisphere was smaller than that in the Northern hemisphere. We found that the spatial patterns of SOG and EOG were strongly correlated with ice/snow cover, altitude, climate, and vegetation types such as CRO.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**PFT**} & \multicolumn{3}{c}{**SOG**} & \multicolumn{3}{c}{**EOG**} \\ \cline{2-7}  & \(\mathbf{R^{2}}\) & **Bias** & **RMSE** & **(Days)** & **R2** & **Bias** & **RMSE** \\  & & **(Days)** & **(Days)** & **(Days)** & **(Days)** \\ \hline OSH + & \(0.79\) & \(2.1\) & \(23.0\) & \(0.24\) & \(4.5\) & \(39.0\) \\ CSH & & & & & & \\ SAV + & \(0.73\) & \(-0.9\) & \(25.2\) & \(0.68\) & \(4.7\) & \(27.5\) \\ WSA & \(0.71\) & \(0.7\) & \(19.3\) & \(0.59\) & \(-0.1\) & \(13.4\) \\ GRA & \(0.90\) & \(-3.4\) & \(15.6\) & \(0.53\) & \(1.4\) & \(25.4\) \\ WET & \(0.60\) & \(1.0\) & \(18.3\) & \(0.58\) & \(-1.2\) & \(16.5\) \\ ALL & \(0.78\) & \(-0.5\) & \(19.4\) & \(0.64\) & \(1.1\) & \(22.9\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Accuracy evaluation for starting day of GPP (SOG) and ending day of GPP (EOG) estimates from the statistical models for non-forest types: open shrublands (OSH), closed shrublands (CSH), savannas (SAV), woody savannas (WSA), grasslands (GRA), croplands (CRO), and wetlands (WET).  
Figure 5: _Cont._