## 1 Introduction  
Vegetation phenology is the study of periodic biological events in the plant world and their relations with environmental factors, such as air temperature and rainfall [1; 2]. As vegetation -phenotype controls the mass and energy exchanges between terrestrial ecosystems and the atmosphere [3; 4; 5; 6], accurate monitoring of vegetation phenology is crucial to assess the interactions between vegetation dynamics and climate change [7; 8]. In the past decades, vegetation spring phenology has attracted a great deal of attention due to its close connection with global change. In contrast, understanding of vegetation autumn phenology is limited, though it can play an important role in determining vegetation growing season length and has been found to be significantly affected by climatic change [9]. Ground-observed phenological data and satellite data are two major tools commonly used to identify vegetation growing season at different scales. Ground data are commonly recorded at the species level and used for conducting species-specific phenology analysis at local scales [10; 11; 12; 13]. Meanwhile, satellite data are mainly employed to define the growing season characteristics of entire landscapes at regional to global scales [14; 15; 16; 17; 18; 19]. Various satellite-derived vegetation indices have been developed to extract vegetation phenological metrics, such as the Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) [20; 21; 22; 23]. Most studies, however, have focused on the spatiotemporal differences of phenological events among diverse biomes or geographic zones [19; 24; 25; 26]. In contrast, only few attempts exist on revealing how vegetation phenology responds to climate change for different vegetation types within a given biogeographic zone at the regional scale. Grassland is a widely distributed vegetation type around the world and plays an important role in providing resources to humankind, supplying feed for animals, and maintaining stability of ecological systems globally [27]. However, plant growth in grassland ecosystems is highly sensitive to regional and global climate change. Several studies have reported higher temporal variations in spring phenology of herbaceous species compared to woody plants and described their complex and controversial response to climate change in temperate grasslands [13; 28; 29; 30]. Most previous studies suggest that a warmer spring results in an advancement of spring phenological events of grassland vegetation [11; 31; 32; 33; 34]. However, under conditions where concurrent precipitation is limiting, increasing temperature may have no significant effects on spring phenology [35; 36]. It has been shown that increasing precipitation had no significant effects on flowering dates in two temperate grasslands of North America [37; 38], while reduced precipitation induced an earlier green-up and flowering of herbaceous species in field experiments [39; 40; 41]. The distinct responses of spring phenology events to climate change in grassland ecosystems may be closely coupled with vegetation types [42]. Our knowledge of the controls regulating autumn phenology of different vegetation types in grassland ecosystems is, however, currently limited. Given the potential differences in climate change impacts, it is crucial to improve our understanding with regard to the responses of both spring and autumn phenological events to climate change among different grassland types. Transhumance provides livestock access to green vegetation during the short periods of active growth in each place. It distributes livestock grazing pressure and lengthens the time period when livestock have access to quality forage [43]. Thus, the transhumance system is closely connected with vegetation phenology. Different vegetation phenology in space not only determines the spatial difference of timing of plant growth [44], but also leads to the spatial heterogeneity of nutritional parameters of pastures [45; 46].