Biotic mechanisms associated with species diversity are expected to stabilize communities in theoretical and experimental studies but may be difficult to detect in natural communities exposed to large environmental variation. We investigated biotic stability mechanisms in a multi-site study across Inner Mongolian grassland characterized by large spatial variations in species richness and composition and temporal fluctuations in precipitation. We used a new additive-partitioning method to separate species synchrony and population dynamics within communities into different species-abundance groups. Community stability was independent of species richness but was regulated by species synchrony and population dynamics, especially of abundant species. Precipitation fluctuations synchronized population dynamics within communities, reducing their stability. Our results indicate generality of biotic stability mechanisms in natural ecosystems and suggest that for accurate predictions of community stability in changing environments uneven species composition should be considered by partitioning stabilizing mechanisms into different species-abundance groups.

The simulation and prediction of the NDVI are conducive to regional ecological restoration. In this research, the Weihe Watershed is selected as the study area, which is located on the eastern edge of the Tianshan tectonic belt. Firstly, according to NDVI characters, we divide the values into five grades, including very low (<0.3), lower (0.3–0.4), medium (0.4–0.5), higher (0.5–0.6), and very high (>0.6), and analyse the NDVI tempo‐spatial variations in Weihe Watershed from 2006 to 2015. Then, we use CA–Markov model with parameters adjustment to simulate and predict the NDVI distributions in 2015 and 2020, respectively. The results show that (a) at temporal scales, the NDVI in Weihe Watershed increase year by year from 2006 to 2015, indicating a better vegetation recovery. At spatial scales, the NDVI increase from north‐west to south‐east gradually, which is related with the main climate factors such as temperature and precipitation. (b) By adjusting the parameters of state transition suitability atlas in the Markov model, we get the model with higher accuracy to simulate NDVI changes. And the Kappa coefficient between the simulation results and the true values is 0.6123. (c) According to the predictions in 2020, the regions with very high NDVI and higher NDVI mainly locate in Qinling Mountains, Guanzhong Plain, Ziwu Mountains, Jinghe Valley, and Luohe Valley. And these regional area percentages occupying the whole watershed increased by 13.62% and 2.64%, respectively, compared with the area percentages in 2015. The regions with medium NDVI, lower NDVI, and very low NDVI mainly distribute at the north Loess Plateau of the watershed. And these regional area percentages occupying the whole watershed decreased by 7.40%, 6.59%, and 2.28%, respectively, compared with the area percentages in 2015. The above results illustrate that the ecological environment of Weihe Watershed is improving, which can provide scientific reference for assessing the regional ecological risk and formulating ecological protection measures.

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Examination of the mechanisms of the plant community assembly at a geographical scale is an interesting topic in ecology and biogeography, which are of great significance for the understanding of species coexistence and biodiversity conservation. But so far, only a few studies have simultaneously assessed the relative roles of multiple-scale factors in shaping the phylogenetic and functional structure of plant communities at a macroecological scale. In this study, we linked modern climate, glacial-interglacial climate change, and soil properties with the phylogenetic and functional structure of shrub and herbaceous plant communities in Inner Mongolia, China, an arid and semiarid region. Our results showed that the functional structure of plant communities was more associated with modern climate and soil properties than the phylogenetic structure, especially for the soil properties. Modern precipitation was found in all the combinations of variables that were most closely related to the community structure in this arid and semi-arid region. These findings suggest that the phylogenetic and functional structure of biotic communities may be affected by processes at divergent spatial-temporal scales. That is, the functional structure is better linked with the modern and local factors while the phylogenetic structure is more associated with the historical and regional processes. This study highlights the importance of the associations between the different biodiversity dimensions and divergent drivers.

Analyzing the encounter frequency of high–low runoff and sediment yield is important for the appropriate dispatching of runoff–sediment resources, as well as river regulation. However, there have been no reports on the utilization of the pair-copula function in analyzing the runoff–sediment characteristics from a probabilistic perspective and conducting probability control on the runoff–sediment yields of different hydrologic stations. This paper builds marginal distribution functions on the basis of kernel distribution theory. In addition, this paper builds the joint distribution functions through pair-copula functions in order to analyze the encounter probability and the compensation characteristics of high–low runoff and sediment at different stations on the Weihe River in China, as well as the origins of runoff–sediment, to conduct probability control of river runoff–sediment resource allocation. The results show that, in different periods, the synchronous probability of high–low runoff of the Weihe River’s Xianyang and Huaxian Stations, and the Jinghe River’s Zhangjiashan Station differ, while that of high–low sediment at the three stations changes little—remaining at around 54%. Therefore, the sediment and runoff of the Weihe River apparently have different origins. In years of high and low runoff, if the runoffs of the Xianyang and Zhangjiashan Stations can be kept within a certain range, then the runoff of the Huaxian Station will be in a particular range, at a certain probability. Sediment at the Huaxian Station can be controlled, in a similar way. These results are of great significance for the water and sediment management department of the Weihe river, in order to reasonably allocate water and sediment resources.