# Estimation of Global Vegetation Productivity from Global LAnd Surface Satellite Data
## 3 Results  
### Temporal and Spatial Variation of Global GPP and NPP  
Using the MuSyQ-NPP algorithm, maps of global estimated 1 km GLASS GPP and NPP in 2004, 2008, and 2012 were obtained, as shown in Figure 3. The highest vegetation productivity (GPP \(>\) 2000 g C\(\cdot\)m\({}^{-2}\), NPP \(>\) 1000 g C\(\cdot\)m\({}^{-2}\)) was found in the humid tropic areas, such as Amazonia, Central Africa and South-east Asia, where both temperature and moisture requirements are fully satisfied for photosynthesis. Temperate regions have an intermediate vegetation productivity (GPP \(\approx\) 1000-1400 g C\(\cdot\)m\({}^{-2}\), NPP \(\approx\) 500-800 g C\(\cdot\)m\({}^{-2}\)), and the lowest vegetation productivity (GPP \(<\) 400 g C\(\cdot\)m\({}^{-2}\), NPP \(<\) 200 g C\(\cdot\)m\({}^{-2}\)) was found in either cold or arid regions, where either temperature or precipitation are limiting factors. Variations in GPP and NPP are demonstrated in Figure 4. In general, from 2004 to 2008, few changes occurred in most areas. The largest GPP increases, about 100 g C\(\cdot\)m\({}^{-2}\), were in Central China and Eastern Russia. In addition, the largest decreases, about 150 g C\(\cdot\)m\({}^{-2}\), occurred in Amazonia and South-eastern Asia. From 2008 to 2012, GPP and NPP increased in most areas. Specifically, the largest increasing trends occurred in tropic areas, such as Amazonia and South-eastern Asia, in which GPP increased by approximately 400 g C\(\cdot\)m\({}^{-2}\) and NPP increased approximately by 200 g C\(\cdot\)m\({}^{-2}\). The next largest increases were seen in areas in Russia, Northern America, and Northeastern China, in which GPP increased by about 100 g C\(\cdot\)m\({}^{-2}\) and NPP increased by about 50 g C\(\cdot\)m\({}^{-2}\). The largest decreasing trends occurred in areas of Eastern Brazil, where GPP decreased by about 300 g C\(\cdot\)m\({}^{-2}\) and NPP decreased by about 150 g C\(\cdot\)m\({}^{-2}\). Global total GPP in 2004, 2008 and 2012 was 108.84 Pg C, 107.30 Pg C and 119.73 Pg C, respectively. Global total GPP estimates are comparable with values of 109.29 Pg C [4], 110.5 \(\pm\) 21.3 Pg C [43] and 132 \(\pm\) 22 Pg C [1]. Global total GPP decreased 1.41% from 2004 to 2008 and increased 11.58% from 2008 to 2012. Global NPP in 2004, 2008 and 2012 was 61.15 Pg C, 60.15 Pg C and 69.53 Pg C, respectively, which was comparable to previously reported values of 56.40 Pg C [44], 56.02 Pg C [4] and values between 39.9 Pg C and 80.5 Pg C with a mean of 54.9 Pg C [45]. Global total NPP decreased by 1.64% from 2004 to 2008 and increased by 15.59% from 2008 to 2012 according to our study (Figure 5). Figure 2: MODerate Resolution Imaging Spectroradiometer (MODIS) International Geosphere Biosphere Program (IGBP) land-cover and location of FLUXNET sites and BigFoot sites. The mean and standard deviation of GPP and NPP for different land cover types are shown in Figure 6. GPP and NPP values were highest in EBF. GPP could be as high as 2799.90 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\), and NPP was approximately 1311.29 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\). GPP and NPP values were lowest in Bare Land: GPP was only 47.25 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\), and NPP was only 25.71 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\). Generally, GPP and NPP in 2012 were higher than these in 2004 and 2008 at all land cover types. GPP and NPP in 2008 were at their minimums among these three years. This is more obvious in EBF. GPP was 3097.35 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\) in 2012, 389.76 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\) more than in 2004 and 502.61 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\) more than in 2008. NPP in 2012 could be as high as 1571.14 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\), 354.75 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\) more than in 2004 and 424.82 g C\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\) more than in 2008. However, in DNF, MF, open shrubland (OSH) and bare land (BL), GPP kept increasing from 2004 to 2012.