The Moving Tendency of Holdridge Life Zone with Its Dry and Wet Climate Changes of Gannan Meadow in Recent 40 Years

Gannan meadow lies in the south-west of Gansu Province, on the northeast border region of Tibet Plateau. Gannan meadow is the core region of the important water source supply area of the Yellow River, which provides a natural defense for the upper reaches, playing a unique role in the water source and eco-environmental security of the Yellow River Basin.Owing to the climate change and the artificial sabotage, the production performance and ecology function of Gannan meadow shows an obvious declining trend in recent years, the grassland degeneration and deserting trend are accelerated, and the phenological of herbage shows an obvious earlier trend. The ecology and environment of Gannan meadow has obviously changed. The Holdridge life zone system is a common used method to study the relation of the vegetative cover and climate, which has an obvious significance of physics and biology. It is widely used in the study of ecology environment, the dry and wet climate changes, the climate regionalization and so on.Most of the meadows in Gannan Plateau are distributed in Hezuo, Xiahe, Luqu and Maqu, so 4 places are selected as representative area to study the moving tendency of Holdridge life zone and dry and wet climate changes of Gannan meadow. Based on the meteorological data, the method of Holdridge life zone is used to analyze the moving tendency of Holdridge life zone and the dry and wet climate changes of Gannan meadow during 1971—2010. The results show that life zone of Gannan meadow still belongs to the subalpine meadow of Tibet Plateau alpine vegetation system. But impacted by the global climate change, the temperature of Gannan meadow increases obviously with the tendency ratio of 0.44—0.46℃ every decade, meanwhile the bio-temperature has increased by 0.23—0.27℃ every decade, too. The variety of precipitation shows a different trend between the northern and southern in Gannan meadow, the moving tendency of Holdridge life zone is diverging from the mean center, and the stability of the Gannan meadow ecosystem is attenuating.The Holdridge R_EPof Gannan meadow shows an obvious ascending tendency in the rate of 0.02—0.03 per decade. After the 1990s, the climate of Gannan meadow shows a warm-drying trend, which is more obvious in the southern of Gannan meadow. The humidity degree of Luqu has changed to humid from the perhumid, and Maqu is in the same transition, too. The most important climatic factor for the Holdridge R_EPincreasing is the temperature, and then is the precipitation and the air humidity.The temperature rising plays a very important role in the warm-drying trend of Gannan meadow.Considering the complexity of the environment and the fragility of the ecology system in the border area of Tibet Plateau, the impact of this change on ecology and environment of Gannan meadow still needs further study.