Regional differences of gramineae herbage phenology and its driving forces in Tianshan Mountains, Xinjiang

The Tianshan Mountains have very complex topographies and the response characteristics of the same kind of vegetation to climate change during its growth period are greatly different as the result of different geographical locations and topographic features. In this study, we analyzed the spatial differences of typical gramineae herbage phenology and the key driving forces by using the meteorological and phenological observation data collected from 1990 to 2015 as well as the mathematical statistics and spatial interpolation methods. The results showed that:(1) During the 26 years, the annual mean temperature and annual mean 0 cm earth temperature increased significantly, and the warming range in the north slope of Tianshan Mountains was greater than that in the south slope. In addition, the annual precipitation varied, roughly being "north slope more, south slope less". Thus, the climate in this region generally showed a warm and humid trend.(2) The phenology of dominant gramineae herbage shared by the four agrometeorological stations in the region of Tianshan Mountains had different features. Generally, the spring greenup date of gramineae herbage started earlier than before, so did its wilting period. Great changes were found in the growth season of the gramineae herbage.(3) The greenup date showed a clear negative correlation with the mean temperatures and mean 0 cm earth temperatures in the current month and spring. For every 1℃ rose in the spring mean temperature, the greenup date was 1.98-5.77 d earlier; for every 1℃ rose in the spring 0 cm earth temperature, the greenup date was 1.40-5.08 d in advance. The dominant factors that affected the wilting dates jointly were the temperature, 0 cm earth temperature and precipitation in the previous three months, which means that the wilting period had an obviously negative correlation with the temperature and 0 cm earth temperature, but a clearly positive correlation with precipitation.(4) The increase of precipitation could promote the growth stage of gramineae herbage when the heat condition was suitable; on the contrary, the increase of precipitation could inhibit the growth stage of the herbage if the heat was insufficient.(5) There was a significant difference in the sensitivity of the herbage growth period to elevation. With the increase of elevation, the response of phenology to climate change was more noticeable.