Geographical Environment of Helanshan National Nature Reserve

Helan Mountain National Nature Reserve is located between Yinchuan Plain and Alashan Plateau, with a NNE-SW trend. It is about 250 kilometers long from north to south, 20-40 kilometers wide from east to west, and the altitude is generally 2000-3000 meters. Aobaogan, the main peak, is located in Inner Mongolia, on the west side of the main river basin, with an altitude of 3556. 1 m. It is customary to divide Helan Mountain into three sections: south, middle and north. The south section is south of Sanguankou, the middle section is from Sanguankou to Dawukou, and the north section is at Dawukou. The scope of this plant survey is about 38 degrees 2 1 min ~ 39 degrees 22 minutes north latitude and 44 minutes ~ 106 degrees 42 minutes east longitude. It is about 140 kilometers long between Sanguankou and Liutiaogou, including the middle and northern sections of Helan Mountain, and the east and west sides include piedmont alluvial fans. Helan Mountain Uplift began with Yanshan Movement in the late Mesozoic, and then experienced long-term denudation and leveling, until Cenozoic and Paleogene, becoming a low-altitude quasi-plain.

The mountainous area where Helanshan National Nature Reserve is located is a mountainous area with an ancient geological history, and the strata are relatively complete. Except for the deposits in the Late Ordovician and Early Carboniferous, most of them are complete from Paleozoic to Quaternary. Precambrian Archean and Proterozoic gneiss and rocks are exposed, which are found in Liutiaogou and Dawukou Gully. Litholites, sandstones and shales of Cambrian in Lower Paleozoic are developed and widely distributed. The Upper Paleozoic is characterized by the equal development of Carboniferous and Permian strata, which are found in Shikanjing, Hulusitai, Suyukou and Shizuishan. It is mainly composed of various sandstones and is one of the main coal-producing strata in this mountainous area. Neither Cretaceous nor Tertiary strata developed. Quaternary alluvial proluvial, aeolian deposits and piedmont deposits are widely distributed in piedmont zone and intermountain lowlands. Helanshan National Nature Reserve is located in the hinterland of Chinese mainland, in the vast arid grassland and desert zone, with a typical continental climate. Winter is controlled by the powerful Mongolian cold high pressure, which lasts for five months. The weather is sunny, dry and cold, and the northwest wind prevails. In spring, the temperature rises rapidly, cold waves often strike, and the weather is unstable and windy. In summer, because the surface temperature rises faster than the ocean, the Mongolian high retreats to the northwest, and the southeast monsoon takes advantage of it. However, because it is far away from the ocean, the humid airflow has become a spent force, with little precipitation, sunny and hot weather and frequent thunderstorms in the afternoon. In autumn, the ground gradually cools down, the continental high pressure system is strengthened again, the northwest wind is dominant again, and the weather is sunny, but it is short-lived. It was frosty in June+10/early October in 5438, and it soon entered winter.

Among various climatic factors, water and heat are important factors affecting the survival and distribution of plants. The water potential conditions in the area where Helan Mountain is located first take the eastern piedmont as an example, starting from Yongning in the south and reaching Shizuishan in the north. Although the altitude gradually decreases, the annual average temperature still decreases with the increase of latitude, from 8.6 degrees Celsius to 8.2 degrees Celsius. In the lowest month (65438+ 10), the average temperature in the south is higher than that in the north, but in the highest month (July), the average temperature is opposite, and the extreme minimum and maximum temperatures also have similar trends, which makes the daily temperature difference in the year and the year higher than 13 degrees Celsius and 3 1 0 degrees Celsius respectively, and the north is higher than the south.

The average annual precipitation is higher in Yinchuan, which is 202.8 mm, and the lowest in Shizuishan, which is 183.3 mm, and gradually decreases from south to north. The seasonal distribution of precipitation is also uneven, concentrated in July-September, accounting for about 60-70% of the annual precipitation, with the highest in July and August. The simultaneous occurrence of rain and heat is beneficial to the growth of plants, resulting in a natural scene of winter drought in Xia Rong.

Bayanhaote on the west side of Helanshan National Nature Reserve is at an altitude of1560m, located in the rain shadow area, and its annual average temperature and annual average precipitation are lower than the same height on the east side, especially the precipitation. For example, Suyukou, located on the east side at an altitude of 1400 meters, has an annual precipitation of 287.2 mm, more than 70 mm, indicating that the climate on the west side of Shanxi is drier and colder than that on the east side.

The change of the above climatic factors reflects that the temperature in the low mountain area of Helan Mountain National Nature Reserve and its surrounding areas changes sharply, with little rain and obvious continental climate. There are many soil types in Helan Mountain National Nature Reserve, and they are regularly distributed with the change of altitude and vegetation types. Calcareous soil is a zonal soil formed under the bioclimatic conditions of desert grassland, which is distributed in low mountainous areas and piedmont alluvial fan areas below 1900 meters above sea level, especially in northern areas. Among them, ordinary calcareous soil is distributed in the foothills and the upper part of alluvial fans, while mountain calcareous soil is distributed in shady slopes and semi-shady slopes of 1400 ~ 1900 meters. The distribution area of calcareous soil is arid, the soil is dry, the soil layer is barren and contains more gravel, generally about 20 ~ 40 cm thick. The mountain gray cinnamon soil is distributed under the shady coniferous forest on both sides of the mountain at an altitude of 1900 ~ 3 100 meters between Sanguankou and Rujigou. The soil layer is about 60 ~ 100 cm thick, and the maximum thickness can reach 150 cm. Fertile soil, high organic matter content and good structure. Due to the different precipitation, it is a common gray cinnamon soil in mountainous areas under 1900 ~ 2350 m Pinus tabulaeformis forest, Populus davidiana forest and hazelnut shrub, which is slightly alkaline and has low water content. The Picea crassifolia forest in 2350 ~ 3 100 meters is a mountain eluviated gray cinnamon soil with a moss layer of 1 ~ 2 cm on the surface and an organic layer of 30 ~ 50 cm below, which is neutral and moist. Meadow soil in mountainous areas is developed under subalpine shrubs and meadow vegetation above 3 100 meters. The soil layer is about 30 ~ 60 cm thick. The surface soil has dense plant roots, high organic matter content and moist and neutral soil. In addition, coarse bone soil is distributed in the steep sunny slope in the north and middle part of the mountain, which is a young soil mixed with stones and thin topsoil. Profile development is weak, hierarchical differentiation is not obvious, organic matter content is very low, and plant growth is sparse. Light brown calcareous soil is developed in the mountainous desert zone below the altitude of 1600 meters on the west side.