**1. Introduction**

As one of the most important and largest terrestrial ecosystems in the world, grasslands cover 30% of the land surface and are mainly distributed in arid and semiarid regions [1]. Due to global climate change and human activity, such as heavy grazing, grasslands in this area have undergone desertification and even virtually disappeared in recent decades [2, 3], making restoration process urgent for degraded grasslands [4, 5]. Current studies about grassland restoration mainly focus on several key components: community composition and structure, species diversity, soil properties and vegetation succession process [6–10]. Grassland is considered very sensitive to climate changes [11–14] and also is influenced by soil resource availability [15, 16].

Compared with forest ecosystem and cropland ecosystem, aboveground net primary productivity (ANPP) of grasslands is highly temporally variable [16, 17]. Specifically, climate-driven variability in grassland productivity has important effects on the global carbon balance, ecosystem service delivery, profitability of pastoral livelihoods and the sustainability of grassland resources [11, 18, 19]. Many ecologists have analysed the impacts of annual precipitation and temperature on ANPP at regional and continental scales [17, 20–23], while numerous site-specific reports have indicated that interannual variability in ANPP is poorly or even not at all correlated with annual climate conditions [19, 24, 25]. Changes in precipitation or temperature during certain parts of the year have been proven to be more relevant drivers of ANPP than annual changes [26–29], and the impacts on vegetation production varied with seasons [13, 28, 30, 31]. For instance, warming in early spring increased grassland productivity by ameliorating cold temperature constraints on plant growth in northern mid- and high latitudes [32, 33] and advancing spring greening phenology [34–36]. Temperature increases in summer; however, it can depress productivity by reducing soil moisture and intensifying physiological stress [13].

The Loess Plateau of China has a total area of about 52 million hectares and is widely known for its fragile ecological environment, frequent severe droughts and problems with water runoff and soil erosion [37]. In recent years, the complicated landscape, frequent droughts and severe soil erosion have attracted worldwide attention and caused sustained deterioration of the ecosystem of this region. In contrast to numerous studies in the temperate grasslands of Inner Mongolia and the alpine grasslands of the Tibetan Plateau, very few reports are available on responses of grassland productivity to climate variability on the more arid Loess Plateau in China [3], especially with respect to responses to seasonal climatic variability. Restoration of the natural vegetation is regarded as the most effective method for changing the ecological environment of the Loess Plateau [7, 8, 38].

As a major determinant of nutrient cycling, litter decomposition is a fundamental process of grassland ecosystem functioning [39]. Decomposition traits of plant litters are affected by a number of factors, including litter quality, abiotic environment and soil organisms [40]. In general, plant litters with high C:N ratio and lignin concentration are supposed to have slow decomposition and nutrient immobilisation processes, whereas low C:N ratio and low lignin concentration contribute to fast decomposition and nutrient mineralisation processes. Decomposition traits of plant materials may vary with succession stages. For example, late-seral dominant grasses normally had high tissue N concentrations, low C:N ratios and lignin concentrations, which result into fast decomposition rate and enhanced nutrient mineralisation.

Most previous studies have focused on plant species richness and diversity in abandoned croplands following short-term grazing exclusion in China [8, 41, 42]. Few studies

**137**

**Figure 1.**

*Location of experimental site.*

determined.

**2.1 Study site**

**2. Material and method**

*Responses of Community Structure, Productivity and Turnover Traits to Long-Term Grazing…*

have reported on the restoration succession of typical natural steppe under long-term grazing exclusion [19, 43]. In the present study, *Stipa* steppe has been fenced from 1982 to the present at Yunwu Mountain National Nature Reserve, and long-term grassland ecological characteristics, productivity and weather records have been collected.

and 5 *Stipa* species are found in our study area. As the constructive species, *S. bungeana* mainly distributed on the Loess Plateau [48]. Noticeably, replacement of dominant *Stipa* species occurred during the long-term restoration process, with *Stipa bungeana* being replaced by *S. grandis* and *S. przewalskyi* [49]. The three *Stipa* species differentiated in their phenotypic traits. In detail, *S. grandis* owns higher plant height, and *S. przewalskyi* possesses more tillers. Besides, *S. bungeana* and *S. przewalskyi* consistently flower and produce seeds earlier than *S. grandis* [49]*.*

The temperature and precipitation variability during 1982–2011 were assessed in this study; the ecological characteristics during long-term grazing exclusion were examined; the relationship between grassland productivity and variation in climate variables were explored; and the variations in decomposition traits of three *Stipa* dominant species (*S. bungeana*, *S. grandis* and *S. przewalskyi*) were

This study was conducted in Yunwu Mountain National Nature Reserve on the Loess Plateau (106°24′–106°28′ E, 36°13′–36°19′ N) (**Figure 1**) [45, 50].

The community in the study area consists of 313 plant species, covering 56 families and 165 genera, with five main families being Compositae, Gramineae, Leguminosae, Rosaceae and Labiatae [44]. The dominant *Stipa* plants include *S. bungeana*, *S. grandis* and *S. przewalskyi*, and main forbs are *Thymus mongolicus*, *Artemisia sacrorum* and *Potentilla acaulis* [45]. Genus-specific morphological and functional traits contributed the dominance of *Stipa* plants in temperate, subtropical and tropical steppe in semiarid areas worldwide [46]. Meanwhile, *Stipa* species showed various adaptabilities to environmental changes, presenting an ecological distribution pattern along the climate gradients [47]. There are 32 species, 1 subspecies and 3 variations in genus *Stipa* plants in China, mainly distributed in western and northeastern area,

*DOI: http://dx.doi.org/10.5772/intechopen.85306*

*Responses of Community Structure, Productivity and Turnover Traits to Long-Term Grazing… DOI: http://dx.doi.org/10.5772/intechopen.85306*

have reported on the restoration succession of typical natural steppe under long-term grazing exclusion [19, 43]. In the present study, *Stipa* steppe has been fenced from 1982 to the present at Yunwu Mountain National Nature Reserve, and long-term grassland ecological characteristics, productivity and weather records have been collected.

The community in the study area consists of 313 plant species, covering 56 families and 165 genera, with five main families being Compositae, Gramineae, Leguminosae, Rosaceae and Labiatae [44]. The dominant *Stipa* plants include *S. bungeana*, *S. grandis* and *S. przewalskyi*, and main forbs are *Thymus mongolicus*, *Artemisia sacrorum* and *Potentilla acaulis* [45]. Genus-specific morphological and functional traits contributed the dominance of *Stipa* plants in temperate, subtropical and tropical steppe in semiarid areas worldwide [46]. Meanwhile, *Stipa* species showed various adaptabilities to environmental changes, presenting an ecological distribution pattern along the climate gradients [47]. There are 32 species, 1 subspecies and 3 variations in genus *Stipa* plants in China, mainly distributed in western and northeastern area, and 5 *Stipa* species are found in our study area. As the constructive species, *S. bungeana* mainly distributed on the Loess Plateau [48]. Noticeably, replacement of dominant *Stipa* species occurred during the long-term restoration process, with *Stipa bungeana* being replaced by *S. grandis* and *S. przewalskyi* [49]. The three *Stipa* species differentiated in their phenotypic traits. In detail, *S. grandis* owns higher plant height, and *S. przewalskyi* possesses more tillers. Besides, *S. bungeana* and *S. przewalskyi* consistently flower and produce seeds earlier than *S. grandis* [49]*.*

The temperature and precipitation variability during 1982–2011 were assessed in this study; the ecological characteristics during long-term grazing exclusion were examined; the relationship between grassland productivity and variation in climate variables were explored; and the variations in decomposition traits of three *Stipa* dominant species (*S. bungeana*, *S. grandis* and *S. przewalskyi*) were determined.
