## 3 Results and Discussions  
### General Characteristics of Vegetation Productivity in the Altay Mountains  
In this study, both the annual GPP and growing season GPP of vegetation in different parts of the Altay Mountains were compared (Figure 2). It can be seen from Figure 2 that the spatial distribution pattern of annual GPP and growth season GPP of vegetation in the Altay Mountains is almost the same, and the proportion of each grade is also very similar. In the whole mountain area, the area with a GPP of 400\(\sim\)600 g c/m\({}^{2}\) has the highest proportion, with annual and growing season proportions of 41.10% and 40.88%, respectively (Table 1). These areas are mainly distributed in the middle- and high-mountain areas in the middle and west parts of the Altay Mountains. The area with a GPP of 200\(\sim\)400 g c/m\({}^{2}\) ranks the second, with annual and growing season GPP proportions of 29.21% and 29.96%, respectively, which are mainly distributed in the areas with a higher altitude in the east and west parts of the Altay Mountains. The area with a GPP of <100 g c/m\({}^{2}\) is the smallest, with annual and growing season GPP proportions of 6.17% and 6.28%, respectively, which are mainly distributed in high-altitude areas in the west and east parts of the Altay Mountains. The GPP of different months in the growing season is significantly different. In this study, the proportion of the area with a different GPP from April to September was compared, and the distributions of the higher GPP area and lower GPP area were analyzed (Figure 3). It can be seen from Figure 3 that, in April, there is still a large area of snow cover in the high-mountain area. In the areas with vegetation coverage, the proportion of the area with a GPP of 1\(\sim\)5 g c/m\({}^{2}\) is the highest, which is 36.73%, and is mainly distributed in the areas below the snow line in the middle part of the mountain. The GPP with 83.73% of the area is less than 15 g c/m\({}^{2}\). In May, the vegetation coverage area expanded and the vegetation GPP increased; the proportion of area with a GPP of 80-120 g c/m\({}^{2}\) is the largest, accounting for 39.04%, which was mainly distributed at the west part of middle- and lower-altitude area. However, there are still lower vegetation coverage areas in this month; the areas with a GPP < 10 g c/m\({}^{2}\) are mainly distributed under the snow line at a high altitude. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Period**} & \multicolumn{5}{c}{**GPP (g c\(\cdot\)m\({}^{-2}\))**} \\ \cline{2-6}  & **\textless{}100** & **100\textasci{}200** & **200\textasci{}400** & **400\textasci{}600** & **>600** \\ \hline Annual (\%) & 6.17 & 9.18 & 29.21 & 41.10 & 14.34 \\ Growing season (\%) & 6.28 & 9.26 & 29.96 & 40.88 & 13.62 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Proportion of the area with a different GPP in annual and growing season. Figure 2: Overall characteristics of annual GPP (**a**) and growing season GPP (**b**) in the Altay Mountains. In June, the vegetation grew vigorously, and the vegetation GPP gradually increased. The proportion of area with a GPP of 100-150 g c/m\({}^{2}\) is the highest, which is 32.58%, and it is widely distributed in the east and middle parts of the mountain. The proportion of the highest vegetation coverage areas with a GPP \(>\) 200 g c/m\({}^{2}\) is 8.18%, which is mainly distributed in the western part of the mountain with a medium altitude. In July, the vegetation GPP of the Altay Mountains was further improved, and the vegetation GPP of most parts of the mountain has a higher value and is relatively consistent. The proportion of area with a GPP of 100-150 g c/m\({}^{2}\) is the highest, which is 36.15%, and is mainly distributed at the east and middle parts of the mountain. In this month, there are still some lower vegetation coverage areas with a GPP \(<\) 50 g c/m\({}^{2}\), accounting for 8.75%, and are mainly distributed at the high-altitude areas in the east and west sections of the Altay Mountains.