Response of Population Structure of Quercus aquifolioides to Altitude Gradient in Sejila Mountain

In this paper, Quercus aquifolioides in Sejila Mountain was taken as the research object, and the population structure characteristics and its changing trend at different altitudes were analyzed. A 50 m × 700 m transect was set up in Sejila Mountain, Nyingchi City, Tibet Autonomous Region, and it was divided into fourteen 50 m × 50 m quadrats. The diameter class, height and crown structure of the population in each quadrat were studied respectively. According to the specific number of distribution plants, the variation rules and causes of different structures were studied according to the charts. The results showed that : (1) The best survival range of Q. aquifolioides was between 3400 m and 3550 m above sea level, and it was not suitable for the survival of Q. aquifolioides above 3600 m. The seedlings and saplings of Q. aquifolioides were distributed at an altitude of 3400 m-3780 m, and the number of trees above 3600 m was less. (2) There were more young seedlings of Q. aquifolioides, and fewer individuals grow to the young tree stage. The young seedlings had strong competitiveness in the growth process, while the competitiveness and viability were weak when they grow to the young tree stage. (3) With the increase of altitude, the diameter distribution range of Q. aquifolioides population gradually decreased, and the population density also decreased. (4) From 3400 m to 3780 m above sea level, the height structure of Q. aquifolioides population increased first and then decreased. (5) From 3400 m to 3500 m above sea level, the canopy structure of Q. aquifolioides population increased continuously, reaching the maximum at 3500 m, and then decreased with the elevation. Soil, water, temperature, and vegetation growth space were different at different altitude gradients, which caused different structural changes in the Q. aquifolioides population at different altitude gradients.