## 2 Material and Methods  
### Description of Study Area  
The Altay Mountains spans China, Kazakhstan, Russia and Mongolia, with a total length of approximately 2000 km. It runs from northwest to southeast. In this study, the Altay Mountains in China is selected as the study area. This area belongs to the south slope of the middle section of the Altay Mountains, with a length of approximately 450 km from east to west and a width of approximately 80-150 km from north to the south. The mountain gradually becomes narrow from northwest to southeast, showing the topographic characteristics of high and wide in the northwest and low and narrow in the southeast (Figure 1), with a total area of 2.6 \(\times\) 10\({}^{4}\) km\({}^{2}\)[33].  
The Altay Mountains has a vast area of forests, grasslands and abundant wetlands, which are important components to maintain the ecological functions of the mountain area. Among them, the forest area is 9802 km\({}^{2}\), accounting for 37.7%, and the total area of the wetland is approximately 800 km\({}^{2}\), accounting for 3% of the total area of the Altay Mountains. The forest is mainly composed of Siberian larch (_Larix sibirica_), and the main arbors include Siberian spruce (_Picea obovata_) and Betula pendula, which, respectively, constitute the larch forest, spruce forest, larch-spruce mixed forest and Betula pendula mixed forest. There is a large number of peat swamps. It is the largest and most complete peat swamp and the key \"carbon pool\" for water conservation in Xinjiang.  
The Altay Mountains, with continental climate characteristics, are located in the hinterland of Eurasia and far from the sea. The spring temperature rises quickly and is windy, the summer is cool and short, the autumn temperature drops quickly and is sunny, and the winter is cold and long. The annual average temperature is approximately \(-2~{}^{\circ}\)C, and the extreme maximum temperature is 33.3 \({}^{\circ}\)C. The mountain area with an altitude of 3100\(\sim\)3300 m is covered with snow all year. The annual average temperature in the middle- and high-mountain area, with an altitude of 1400-2600 m, is below \(-9~{}^{\circ}\)C, and is the hottest in July, which is only approximately 15 \({}^{\circ}\)C. The annual temperature difference is approximately 30 \({}^{\circ}\)C, and the daily temperature difference is approximately 12 \({}^{\circ}\)C. The annual average temperature in the low-mountain and hilly area is below 4 \({}^{\circ}\)C. The altitude increases by 100 m, and the annual precipitation increases by 30/80 mm. The annual precipitation is 200-300 mm in the low-mountain belt, 300-500 mm in the middle-mountain belt, and 600-800 mm in the high-mountain belt, and decreases from north to south and from west to east. The Altay Mountains are an important natural forest area in Xinjiang, known as the ecological protective screen in the north of Xinjiang. The total area of the forest is \(69~{}\times~{}10^{4}\) km\({}^{2}\), and the standing forest volume is \(9.197~{}\times~{}10^{4}\) m\({}^{3}\), accounting for 47% of the natural forest in Xinjiang [14; 34; 35].  
Figure 1: Location of Study Area (Driving number of map: GS (2019) 1823).