What is the relationship between the northern limit of Chinese orchid distribution and mountain ranges?

The Kunlun-Qinling range is a complete mountain system stretching 5000 km across China. The Kunlun Mountains have many snow peaks, glaciers, volcanoes and hot springs. From the Pamirs to the Sichuan Basin it extends 2500 km, at an elevation of 5000-7000 m, with the main peak Muztagh Mountain at 7723 m, a snow line at 5500 m and an ice layer 200 m thick; it is known as the "Father of Icebergs", and Chinese orchids cannot survive there. The Qinling range starts in the west at the border between Gansu and Qinghai provinces and reaches central Henan in the east, with a total length of 1500 km. The summit terrain is gentle, taking a plateau form, indicating a flat expanse, and the weathered layer is still very deep. The mountain rises 220-3000 m, with the main peak Taibai Mountain at 3767 m. On the northern side faults have subsided, making the mountain grandeur. Glaciers, trough valleys and horn peaks are distributed there. Like a wind-blocking wall, it intercepts the cold current moving south and turns the Sichuan Basin south of the mountain into a warm area. For example, Chengdu (30 degrees 40'N), although at an elevation of 508 m, has the same temperature as Hangzhou (30 degrees 14'N) at an elevation of only 43 m, with an annual average of 16.2 degrees for both. It also blocks the moist air current moving north, making the area north of the mountain an arid zone. For example, Xi'an (34 degrees 18'N) has annual precipitation of only 580.2 mm, while Xuzhou (34 degrees 17'N) has annual precipitation of 848.1 mm. Therefore, the Qinling is the dividing mountain between north and south. South of the mountain it is warm and suitable for the growth of Chinese orchids, while north of the mountain it is arid and cold (Xi'an annual precipitation 580.2 mm, annual average 13.3 degrees), unsuitable for the growth of Chinese orchids, which agrees with Chen Xinqi's regionalization. The hills of central Shandong were formed 5 million years ago as a dome on the basis of a crustal thickness of 35 km, and gradually sank into the flat North China Plain. At the top of the dome are Mount Tai (elevation 1524 m), and the block mountains Mengshan (1156), Lushan (1108) and Yishan (1032). The most famous, Mount Tai, is composed of gneiss, granite and limestone. Gneiss and granite have similar composition, and the soil formed by their weathering is acidic, such as the chestnut orchard on the western slope of Mount Tai. The soil formed by the weathering of limestone is alkaline. But the mountains of central Shandong are mainly limestone, so acidic soil is lacking. Only acidic soil is suitable for the growth of Chinese orchids (Editor's note: weakly acidic and neutral soils can both produce orchids, while alkaline soil is unsuitable). Liangshan County in Shandong has mountains, and Jiaxiang County also has them; these two counties may be places Confucius passed through when returning to Lu from northern Henan. Their mountains are limestone formed by long-term deposition under a water depth of 60 m. The soil formed by the weathering of this rock is alkaline, which is not conducive to the growth of Chinese orchids. (Wang Tao)