Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee Changes in vegetation parameters and soil nutrients along degradation and recovery successions on alpine grasslands of the Tibetan plateau Na Guo a , A. Allan Degen b , Bin Deng a , Fuyu Shi a , Yanfu Bai a , Tao Zhang a , Ruijun Long a , Zhanhuan Shang a, ⁎ a School of Life Sciences, State Key Laboratory of Grassland Agro-ecosystems, Lanzhou University, Lanzhou, 730000, China b Desert Animal Adaptations and Husbandry, Wyler Department of Dryland Agriculture, Blaustein Institutes for Desert Research, Ben-Gurion University of Negev, Beer Sheva, 8410500, Israel ARTICLE INFO Keywords: Vegetation parameters Soil stoichiometry Degradation succession Recovery succession Enclosure Alpine grassland ABSTRACT Understanding the changes in vegetation parameters and soil nutrients in the different stages of grasslands degradation and recovery is crucial for assessing and restoring degraded grasslands. Consequently, we de- termined above-ground vegetation and soil C, N and P concentrations and their stoichiometry in different de- gradation and recovery stages on the Tibetan Plateau. Four degradation succession stages, GKC: Grass-Kobresia community, KHC: Kobresia humilis community, KPC: Kobresia pygmaea community, and FBC: forbs - black soil beach community, and three recovery succession stages, FG: freely grazed, RG: restricted grazed, and NG: non- grazed, were identified. Above-ground biomass and vegetation coverage decreased with degradation succession and there was a concomitant shift of plant functional groups to more above-ground biomass of forbs and less biomass of grasses and sedges. The highest species diversity emerged in the K. pygmaea succession stage, mainly due to an influx of Compositae. Significant differences in soil total nitrogen (TN), total phosphorus (TP) and soil organic carbon (SOC) concentrations occurred in the 0–10 and 10–20 cm layers among degradation successions. Vegetation cover, above-ground biomass, soil TN and SOC, as well as C:N and C:P ratios increased in non-grazed grasslands when compared to grazed grasslands. Soil TN, TP and SOC concentrations decreased with increasing soil depths across all degradation and recovery successions. In addition, soil nutrients and their stoichiometry were affected by above-ground biomass. We concluded that grazing exclusion could improve the above-ground vegetation and soil nutrients of degraded alpine grasslands, but that the rate of recovery was related to the degree of degradation. 1. Introduction Alpine grasslands account for 70% of the total territory on the Tibetan Plateau and contain approximately 4% of the world’s grass- lands soil carbon (10.7 Pg C) and 0.7%–1% of the total global nitrogen (0.92 Pg N) (Ni, 2002; Tian et al., 2006). The grasslands play a key role in the livelihood of herders, but for this practice to be sustainable, a proper balance must be maintained between grazing livestock and grassland productivity (Zhang et al., 2007; Feng et al., 2010). This, however, has not occurred, as the grasslands have been seriously de- graded since the 1980s, causing losses in grassland biodiversity, water retention capability, soil nutrients and opportunities for recreation (Andrade et al., 2015; Chen et al., 2017). As a result, there has been a decline in ecosystem services, including the provision of pasture and habitat for domestic and wild animals, support of plant biodiversity and soil fertility and regulation of soil nutrients and hydrological regimes due to a reduction of native plant species and plant productivity. Heavily and severely degraded alpine grasslands (“black soil beach”) have reached 34% and 8%, respectively, of the grasslands in the headwater region of major Asian rivers (the Yangtze, Yellow and Lan- cang Rivers) on the Tibetan Plateau (Shang et al., 2008; Wang et al., 2014). Grassland degradation is characterized by diverging regional gra- dients, depending on soil, climate and management (Wang et al., 2018). Degraded grasslands not only alter the plant succession process on the alpine ecosystem (Williamson et al., 2016), but they are extremely slow to recover (Babel et al., 2014). Therefore, the recognition of degrada- tion level is crucial in the restoration and maintenance of degraded alpine grasslands. With grassland degradation, there was a decrease in soil fertility due to losses in total C, total N and available N, total P and https://doi.org/10.1016/j.agee.2019.106593 Received 23 March 2019; Received in revised form 25 June 2019; Accepted 27 June 2019 ⁎ Corresponding author. E-mail address: shangzhh@lzu.edu.cn (Z. Shang). Agriculture, Ecosystems and Environment 284 (2019) 106593 0167-8809/ © 2019 Elsevier B.V. All rights reserved. T