The world is faced with dual challenges to ensure food security for its large and still growing population and to mitigate climate change. It is necessary to develop more diversified and multifunction agricultural systems to address the challenges. Therefore, as a reasonable land use practice, agroforestry has become the hotspot in scientific research in recent decades. This study performed quantitative and qualitative analyses of agroforestry research published between 1990 and 2018 based on bibliometric methods, expecting to guidance for further research in order to scientifically understand of the trends and features of agroforestry research over time and by region. A total of 4204 publications were obtained from Web of Science. The results show that the research interest in the agroforestry field has significantly enhanced, and about 139 countries have been involved with the research in this field. These publications cover 66 subject categories and a great diversity research theme. Since 1990, the popular keywords in agroforestry research have been changed from “Intercropping”, “Alley cropping”, and “Multipurpose trees” to “Carbon sequestration”, “Ecosystem service”, and “Climate change”. This indicates that the theme of agroforestry research has changed and the research scale is gradually expanding. Furthermore, agroforestry research themes vary with regions, since different regions have various requirements on the function of the agroforestry system. In the end, given the current trend of agroforestry science, we conclude a list of research potentials of agroforestry in the future.

Fine root is of importance in biogeochemical cycles especially in terrestrial ecosystems. The lack of understanding of the factors controlling root lifespan has made accurate prediction of carbon flow and nutrient cycling difficult. A controlled warming experiment was performed in an alpine meadow on the northern Tibetan Plateau (near Nagchu Town). We used a minirhizotron technique to measure root dynamics in situ during the growing season of 2013 and 2014 and survival analyses to assess root lifespan and the effects of root diameter, branch order, birth season, root depth and warming on root lifespan. Root diameter, branch order and root depth were all positively correlated with root lifespan. With an increase in diameter of 0.1 mm, mortality hazard ratio of roots declined by 19.3 %. An increase in one level in branch order was associated with a decrease of 43.8 % in root death ratio. Compared with roots born in May–mid‐July, the mortality hazard ratio of roots born in late July–August and September–October reduced by 26.8 and 56.5 %, respectively. In warming treatments, roots tended to be thinner, less branched and deeper, and there was a higher proportion of roots born in spring compared to ambient conditions. Warming shortened the median root lifespan 44 days. However, in single warming condition, root diameter had no significant influence on root lifespan. Root diameter, branch order, root depth and season of birth were all factors affecting root lifespan in the alpine meadow; however, root branch order was dominant.

The Qinghai-Tibetan Plateau (QTP) has the world’s largest alpine grassland ecosystem. The QTP ecosystem is extremely fragile and suffers continuous degradation. An accurate determination of the status of alpine grassland is the first crucial step in monitoring its degradation. A novel method combining field survey with remote sensing information based on ecological indicators is proposed. The degradation classification of alpine grassland was identified by multivariate hierarchical analysis based on 270 field plots. The spatial pattern of alpine grassland degradation was mapped by determining remote sensing variables that corresponded to field indicators of the degradation classification system. The results showed that clustering analysis divided the degradation classification of alpine grassland into five classes: Non-Degraded (ND), Slightly Degraded (SLD), Moderately Degraded (MD), Severely Degraded (SD), and Extremely Degraded (ED). The most significant factors for alpine grassland degradation included the dominance of Cyperaceae plants, soil total nitrogen content, soil organic carbon content, soil total carbon content, soil bulk density, soil pH, dominance of miscellaneous plants, and elevation among all 17 variables. The assessment and mapping of alpine grassland degradation provide an important basis for alpine grassland protection and management, particularly at a large scale.

Aboveground net primary productivity (ANPP) and rain-use efficiency (RUE) are important indicators in assessing the response of ecosystems to climate change. In this paper, the Changtang Plateau in the Tibetan Autonomous Region was selected as the study area to analyze the spatial and temporal changes of ANPP and RUE in grassland communities and their response to climate change. The results showed the following:(1) The spatial pattern of ANPP was closely related to rainfall on the Changtang Plateau. The average ANPP over the past 15 years increased gradually from the arid west to the humid east. A consistent pattern was exhibited in different grassland types and climate zones. (2) The RUE was higher at the east and west edges of the Changtang Plateau, especially in the arid west, but was lower in the center. From the perspective of different climatic zones, the average RUE in the southern Tibetan semiarid climate zone and the Ngari arid climate zone was significantly higher than that in other climate zones. However, the average RUE in different grassland types only varied from 0.07 to 0.09 g·m⁻²·mm⁻¹. The spatial variation in RUE was more distinct in different climatic zones than in different grassland types. (3) Climate change influenced the interannual variation of ANPP and RUE, but the response of ANPP to rainfall showed a significant lag. The interannual change in RUE was negatively correlated with changes in precipitation. (4) In general, a greater area showed a significant increase rather than a decrease in ANPP on the Changtang Plateau, which meant that the grassland condition is improving. The temporal variation patterns of ANPP and RUE in different climate zones were consistent with the overall patterns on the Changtang Plateau, while the variation was not significant in different grassland types.

Alpine treeline ecotones are harsh environment for tree establishment due to low temperature. Tree establishment at treelines requires favorable climate, suitable microsites, and viable seeds. But most researches have been addressed treeline microclimate and its effects on tree regeneration, the knowledge of seed quantity and quality and its controls on seedling recruitment were limited. We measured seed rain, soil seed bank, seed germination rate and seedling recruitment in natural forests in combination with seed transplanting manipulation to evaluate the controls of seed quantity and quality on seedling recruitment of Abies georgei var. smithii (smith fir) along altitudinal gradient, with focus on treeline ecotone in the Sygera Mountains, southeastern Tibetan Plateau. Both seed quantity and seed quality of smith fir decreased with increasing altitude and was thereby associated with decline in seed germination rate. Seed quantity and seedling recruitment were better in north-facing slope than in south slope. The treeline ecotone above 4200 m appeared as the threshold altitude to sharply decrease seed quality and seedling recruitment. The emergence and overwintering rates of transplanting seeds from 3600−3800 m also went down remarkably above 4200 m at north-facing slope. It also underpins the fact that treeline ecotone is the bottleneck of seedling recruitment. Our results suggest that seed quantity and quality are the principal limitation of treeline upward advance. This study also provides evidence to support stable treeline position in southeastern Tibetan Plateau.