This is mainly caused by the difference in climatic conditions from the flat to the top of the mountain. This difference is mainly manifested in: the difference in degree. Every time the altitude rises by 100 m, the temperature will drop by 0.5 ~ 1 degree Celsius. As the mountain rises, not only does the temperature drop, but the temperature difference between day and night is also greater. During the day, the temperature rises higher because of the strong light, but at night, the temperature usually drops greatly, even below 0 degrees Celsius. Too low temperature at night will inhibit the growth of plants. The difference in temperature. With the elevation, the humidity is also increasing. The increase of humidity affects the normal transpiration of plants, the absorption of water by roots, and the timely supply of nutrients, thus affecting the growth of plants. The difference in light. Because the atmosphere on the top of the mountain is thin, there are few clouds, and sunlight is particularly easy to reach here through the atmosphere, so the ultraviolet rays of sunlight in the mountains are stronger than those in low-lying areas. Due to the reflection and refraction of the atmosphere, ultraviolet rays are weak in low-lying areas, and ultraviolet rays can inhibit the formation of long elements in plants, thus inhibiting the elongation of plant stems. People who are used to climbing mountains will find that when people go up the mountain, plants will appear shorter. When they reach the top of the mountain, plants will become very short, and some will look like rosettes. Maybe you will be surprised to ask, why is this? The growth of plants is not only related to themselves, but also related to the surrounding environment. Although some of the ultraviolet rays in the sun are absorbed by the ozone layer, a small part can reach the ground, especially in mountainous areas. Because ultraviolet rays can inhibit the elongation of stems, many alpine plants are short. There are other factors. The top of the mountain is very high above sea level, and the temperature decreases with the elevation. The temperature drops by 0.5℃ ~ 0.6℃ per 100 meter. But because low temperature is not conducive to plant growth and development; And shorter plants are good for heat preservation. Alpine soil is very loose and the terrain is steep. The nutrients in the soil are more easily washed away by rain, and the soil is barren. Plants can not get rich nutrition, which affects their growth and development. Another important feature of high mountains is strong winds. In order to prevent plants from being blown down by the wind, the stems of plants often become shorter.