Grazing exclusion is one of the most efficient approaches to restore degraded grassland but may negatively affects the recovery of species diversity. Changes in plant species diversity should be a consequence of the e...Grazing exclusion is one of the most efficient approaches to restore degraded grassland but may negatively affects the recovery of species diversity. Changes in plant species diversity should be a consequence of the ecological assembly process. Local community assembly is influenced by environmental filtering, biotic interactions, and dispersal. However, how these factors potentially contribute to changes to species diversity is poorly understood, especially in harsh environments. In this study, two management sites within a Stipa breviflora desert steppe community（typical natural steppe） were selected in northern China. In one of the two management sites, grazing has been excluded since 2010 and in the other with open grazing by sheep. In August 2016, three plots were established and 100 sampling units were created within each plot in a 5 m×5 m area at the two management sites. To assess the effects of grazing exclusion on S. breviflora steppe, we analyzed the vegetation biomass, species diversity,soil organic carbon, and soil particle size distribution using paired T-tests. In addition, variation partitioning was applied to determine the relative importance of environmental filtering and dispersal limitation. Null mode analysis was used to quantify the influence of biotic interactions in conjunction with Eco Sim niche overlap and co-occurrence values. Our results demonstrated that（1） species diversity significantly decreased and the main improvements in soil quality occurred in the topsoil 0–10 cm after the grazing exclusion;（2） environmental filtering was important for community assembly between grazed and fenced grassland and this appears particularly true for soil particle size distribution, which may be well correlated with soil hydrological processes; and（3） however, competitive exclusion may play a significant role within the exclusion. The multiple pathways of assembly may collectively determine negative effects on the restoration of species diversity. Therefore, designers should be aware of the risk of reducing grazing exclusion-induced species diversity and account for manipulating processes. This in turn will reduce dominant species and promote environmental heterogeneity to maximize species diversity in semi-arid regions.展开更多
Distribution of rainfall event sizes and interval lengths between events are important characteristics of arid and semi-arid climates. Understanding their importance will contribute to our ability to understand ecosys...Distribution of rainfall event sizes and interval lengths between events are important characteristics of arid and semi-arid climates. Understanding their importance will contribute to our ability to understand ecosystem dynamics in these regions. Rainfall event timing and magnitude are important drivers of ecosystem processes and are instrumental in creating land-scape heterogeneity in arid and semi-arid regions. Rainfall event characteristics were analyzed using an automatic tip-ping-bucket rain-gauge record across the entire summer monsoon season from 2008 to 2015 at the arid desert area of Shapotou in the Tengger Desert, China. Changing the minimum inter-event time （MIT） from 30 min to 24 h alters the number of rainfall events from 64 to 25 for the event depth larger than 0.1 mm. The mean rainfall intensity declined from 0.95 mm/h to 0.53 mm/h, and the geometric mean event duration rose from 0.55 h to 4.4 h. The number of rainfall events, mean rainfall intensity, and geometric mean event duration differed under different criteria of individual rainfall depths, except that for an individual rainfall depth of 0.5, 1.0, and 5.0 mm. The aforementioned features differed only at the lowest range of the mean rainfall intensity and depth for MIT=3 and 6 h. These findings suggest that identification of event-based rainfall in this specific arid region can be better achieved by setting the MIT at six hours. The wide variation in rainfall event properties indicate the need for paying more attention to the proper selection and reporting of event criteria in studies that adopt event-based data analysis. This is especially true in quantifying effective rainfall for soil water replenishment in terms of rainfall depth and intensity with infrequent rainfall events.展开更多
鉴于陆面模式在干旱半干旱区模拟性能较差,本研究运用Common Land Model(CoLM)陆面模式对中亚干旱荒漠草地生态系统进行了站点验证,检验其在该区域的模拟性能,并分析了其陆面特征。结果表明,不同水分状况的草地生态系统在能量分配上表...鉴于陆面模式在干旱半干旱区模拟性能较差,本研究运用Common Land Model(CoLM)陆面模式对中亚干旱荒漠草地生态系统进行了站点验证,检验其在该区域的模拟性能,并分析了其陆面特征。结果表明,不同水分状况的草地生态系统在能量分配上表现出明显的差异性,干旱特征明显的阜康站和咸海站能量分配表现为以感热通量为主;水分状况较好的巴尔喀什湖站能量分配以潜热通量为主。CoLM陆面模式对典型干旱荒漠草地生态系统的陆面过程有较好的模拟性能,能正确描述能量通量的日变化特征。模型对研究站点夜晚感热通量、土壤热通量的模拟效果不太理想,夜间感热通量模拟值略高于观测值,土壤热通量模拟明显低于观测值,在3个研究站点土壤热通量偏差均大于50 W/m^2,不能很好地描述昼夜温差较大的干旱区夜间较强的土壤热通量交换过程。展开更多
基金financially supported by the National Natural Science Foundation of China (41461046,31760707)
文摘Grazing exclusion is one of the most efficient approaches to restore degraded grassland but may negatively affects the recovery of species diversity. Changes in plant species diversity should be a consequence of the ecological assembly process. Local community assembly is influenced by environmental filtering, biotic interactions, and dispersal. However, how these factors potentially contribute to changes to species diversity is poorly understood, especially in harsh environments. In this study, two management sites within a Stipa breviflora desert steppe community（typical natural steppe） were selected in northern China. In one of the two management sites, grazing has been excluded since 2010 and in the other with open grazing by sheep. In August 2016, three plots were established and 100 sampling units were created within each plot in a 5 m×5 m area at the two management sites. To assess the effects of grazing exclusion on S. breviflora steppe, we analyzed the vegetation biomass, species diversity,soil organic carbon, and soil particle size distribution using paired T-tests. In addition, variation partitioning was applied to determine the relative importance of environmental filtering and dispersal limitation. Null mode analysis was used to quantify the influence of biotic interactions in conjunction with Eco Sim niche overlap and co-occurrence values. Our results demonstrated that（1） species diversity significantly decreased and the main improvements in soil quality occurred in the topsoil 0–10 cm after the grazing exclusion;（2） environmental filtering was important for community assembly between grazed and fenced grassland and this appears particularly true for soil particle size distribution, which may be well correlated with soil hydrological processes; and（3） however, competitive exclusion may play a significant role within the exclusion. The multiple pathways of assembly may collectively determine negative effects on the restoration of species diversity. Therefore, designers should be aware of the risk of reducing grazing exclusion-induced species diversity and account for manipulating processes. This in turn will reduce dominant species and promote environmental heterogeneity to maximize species diversity in semi-arid regions.
基金funded by the National Natural Science Foundation of China (Grant Nos. 41530750, 41501108 and 41371101)
文摘Distribution of rainfall event sizes and interval lengths between events are important characteristics of arid and semi-arid climates. Understanding their importance will contribute to our ability to understand ecosystem dynamics in these regions. Rainfall event timing and magnitude are important drivers of ecosystem processes and are instrumental in creating land-scape heterogeneity in arid and semi-arid regions. Rainfall event characteristics were analyzed using an automatic tip-ping-bucket rain-gauge record across the entire summer monsoon season from 2008 to 2015 at the arid desert area of Shapotou in the Tengger Desert, China. Changing the minimum inter-event time （MIT） from 30 min to 24 h alters the number of rainfall events from 64 to 25 for the event depth larger than 0.1 mm. The mean rainfall intensity declined from 0.95 mm/h to 0.53 mm/h, and the geometric mean event duration rose from 0.55 h to 4.4 h. The number of rainfall events, mean rainfall intensity, and geometric mean event duration differed under different criteria of individual rainfall depths, except that for an individual rainfall depth of 0.5, 1.0, and 5.0 mm. The aforementioned features differed only at the lowest range of the mean rainfall intensity and depth for MIT=3 and 6 h. These findings suggest that identification of event-based rainfall in this specific arid region can be better achieved by setting the MIT at six hours. The wide variation in rainfall event properties indicate the need for paying more attention to the proper selection and reporting of event criteria in studies that adopt event-based data analysis. This is especially true in quantifying effective rainfall for soil water replenishment in terms of rainfall depth and intensity with infrequent rainfall events.
文摘鉴于陆面模式在干旱半干旱区模拟性能较差,本研究运用Common Land Model(CoLM)陆面模式对中亚干旱荒漠草地生态系统进行了站点验证,检验其在该区域的模拟性能,并分析了其陆面特征。结果表明,不同水分状况的草地生态系统在能量分配上表现出明显的差异性,干旱特征明显的阜康站和咸海站能量分配表现为以感热通量为主;水分状况较好的巴尔喀什湖站能量分配以潜热通量为主。CoLM陆面模式对典型干旱荒漠草地生态系统的陆面过程有较好的模拟性能,能正确描述能量通量的日变化特征。模型对研究站点夜晚感热通量、土壤热通量的模拟效果不太理想,夜间感热通量模拟值略高于观测值,土壤热通量模拟明显低于观测值,在3个研究站点土壤热通量偏差均大于50 W/m^2,不能很好地描述昼夜温差较大的干旱区夜间较强的土壤热通量交换过程。
