South Qilian Mountain Ecological Zone (Ⅰ)

The South Qilian Mountain Ecological Zone is located in the Qilian Mountain area above the Heihe Valley, including most of Qilian County in Qinghai Province and some areas in Sunan, Gansu Province. Qilian Mountain extends to the northwest, stretching nearly Qian Qian meters, with high terrain, with an average elevation of more than 3,000 meters, and permafrost is distributed in most areas. Influenced by the climate of Qinghai-Tibet Plateau and Mengxin Desert, the climate is cold and humid, the precipitation increases with the elevation, and the water resources are abundant, which makes the northern foot of Qilian Mountain the birthplace of Shiyang River, Heihe River and Shule River, and provides essential water resources for Hexi Corridor.

1. Vegetation characteristics

Landscape types: The exposed bedrock of the northern margin of Qinghai-Tibet Plateau, such as ridges, snow-capped mountains, glaciers, grasslands, forests, rivers, farmland and other landscape elements, constitute nonlinear patches with different characteristics. The exposed bedrock patches are distributed in several bands along the northwest of the mountain range, stretching for hundreds of kilometers; Snow mountains and glaciers are embedded in irregular patches of exposed bedrock; Alpine meadow patches are distributed in strips on gentle slopes, valleys and river valleys on both sides of bare bedrock patches; The patches of alpine shrub grassland and arid grassland are distributed in the Zhongshan area near Hexi Corridor in a strip shape. Spruce forest belt is embedded in alpine shrub grassland in blocks. The landscape zoning is obvious.

Community type: There are two vegetation communities, grassland and forest, which can be divided into alpine meadow grassland, alpine shrub grassland and arid grassland. The forest is spruce forest and shrub forest. Kobresia tibetica, Kobresia alpina and Kobresia humilis are the main constructive species of alpine meadow, accompanied by edelweiss and Carex. In the alpine shrub grassland, the main constructive species are Salix, Caragana sagittata and Prunus mume, and the plants under the shrub are complex, including Kobresia humilis, Leontopodium and Carex. The main constructive species of forest is Picea crassifolia, and there are Sabina vulgaris in some places. There are shrubs such as willow, boxwood and poplar under the forest. 2. Vegetation zoning

The distribution of vegetation community is controlled by altitude and precipitation, and the vertical zoning is obvious, which can be divided into 6 subregions.

Sub-region ia: It is a snow-capped mountain glacier belt, located in the mountainous area above 4800 meters above sea level, with a precipitation of more than 500 mm. It is a permafrost distribution area, covered with snow and ice all year round, without vegetation, and the ecological conditions are extremely bad.

Subzone Ⅰ B: It is a high mountain desert zone, located on the ridge above 4500 meters above sea level, with exposed bedrock and strong physical weathering. The surface layer is cold desert soil, and the vegetation types are mainly cushion plants, such as plum blossom, jellyfish Saussurea involucrata, Paris polyphylla and Rhodiola. The community coverage rate is less than 15%, and the ecological conditions are extremely bad.

Sub-zone I c: Alpine meadow area, located in the gentle slope of the valley at an altitude of 3300-4000m, with rainfall of 400~500mm. Most of the low-lying areas in the ravine are alpine swamp meadows, and the groundwater depth is 0.5~2.0m, which belongs to the seasonal melting zone of permafrost. The surface layer is alpine meadow soil, and the vegetation types are KOBRESIA tibetica, KOBRESIA alpina, Carex and Euphorbia humilis, and the community coverage is 70.

Sub-zone Ⅰ D: Alpine shrub grassland zone, located in the mountainous area with an altitude of 3200 ~ 3800 meters, with rainfall of 330 ~ 500mm ... The groundwater depth is greater than 100m, and the water-rich amount is less than 100m/d3. The vadose zone is characterized by seasonal frozen soil, hydrochemical type is HCO3, salt content is less than 1.0g/L, the surface layer is subalpine meadow soil, shrub types are Yanagi Takayama, Mume and Caragana sagittata, and herbs under the shrub are mainly Carex and Crotalaria.

Subzone Ⅰ e: spruce forest belt, with an altitude of 2,500-3,300m and rainfall of 250-350mm. The buried depth of groundwater is more than 100m, the water abundance is less than 100m/D3, the hydrochemical type is HCO3, and the salinity is less than1.0g/L. The surface layer is gray cinnamon soil, and the vegetation type on the shady slope is Picea crassifolia, with shrubs such as Buxus buxus and Populus tomentosa under the forest, and Sabina przewalskii on the sunny slope, which is in good ecological condition.

Sub-zone Ⅰ G: It is a grassland belt with an altitude of 2300 ~ 2800 meters and a rainfall of 200 ~ 300mm ... The buried depth of groundwater is greater than 100m, and the rich water is less than 100m/d3. There is a lot of chestnut soil on the surface. Vegetation types include Stipa purpurea, Stipa grandis, Leymus chinensis and Artemisia ordosica. The coverage rate is mostly between 50% and 70%, and the ecological conditions are good. See Table 9-8.

Table 9-8 Eco-geological Zoning Table of Heihe River Basin

3. The function of vegetation as water source culvert.

Qilian Mountain has good vegetation coverage, which is distributed in alpine meadows in Heihe River basin, tributaries and gentle slopes, with high coverage and good water conservation function. Woodland, shrub grassland and dry land grassland developed on sloping land have the functions of slowing down the surface water flow speed, increasing precipitation infiltration, prolonging runoff duration and reducing flood peak. Among them, alpine meadow ecosystem and spruce forest ecosystem with high coverage and widest distribution area have the best water conservation ability. In the upper reaches of Heihe River, compared with the watershed with forest coverage of 32%, the runoff of the watershed with forest coverage of 65% increased by 28.87mm in dry season and decreased by 98.90mm in flood season, and the flood peak (26.6mm) formed by single precipitation was delayed by 2.5h hours. Forest vegetation affects the runoff process from beginning to end, and will not reduce the total amount of river runoff (Wang Jinye et al., 1998). The vegetation ecosystem in Qilian Mountains is good, which plays an indispensable role in ensuring the water stability of Heihe River system.