Abstract: As a sensitive transitional zone between forest and tundra, timberline has always been considered by ecologists to be an ecologically fragile zone, an amplifier of outside interference signals, and a global climate change early warning zone. Since the 1980s, many studies have been made on the effects of global climate change on alpine timberline, mainly addressed the relationships of the upper limits of timberline with altitude and latitude, and in particular, the responses of timberline location to global warming. Several hypotheses were proposed to examine the timberline formation of various tree species affected by environmental factors. This paper summarized these hypotheses, and discussed some potential studies in the future.

Key words: Citrus, Fruit quality, Sugar, Organic acid, Total soluble solid, Ecological factors