藏北高寒草地植被和土壤对不同放牧强度的响应

放牧压力在时间和空间的不均衡分布导致局部土地过度利用和生态退化，然而当前对放牧强度的量化多采用替代性指标或对照试验，缺乏直接监测数据，也缺乏不同草地类型对放牧强度变化的响应差异性研究。以西藏自治区那曲市为研究区，利用佩戴式GPS牛羊定位器构建高精度放牧轨迹数据集模拟放牧强度，构建栅格尺度放牧强度空间分布和划分方法，结合草地群落样方调查，通过Duncan法（Duncan''s multiple comparative analysis）进行多重比较分析，探究自由放牧模式下高寒草甸和高寒草原两类区域植被和土壤对不同放牧强度的响应方式及差异性。本研究可为放牧行为环境效应监测提供新思路，并根据不同草地状况因地制宜提出放牧优化管理策略，助力高寒传统牧区的可持续发展。主要结论有：1）随着放牧强度的增大，高寒草原地上生物量先升高后降低，高强度放牧对高寒草原植被的影响大于高寒草甸。2）高放牧强度下，高寒草原土壤水分显著高于中低强度，高寒草甸土壤容重显著低于低强度。可能原因是放牧压力多集聚于水源附近。高寒草原区土壤的砂粒含量随放牧强度的增大而增加。放牧强度的增大导致草甸上层土壤有机质增加，草甸下层、草原上层、草原下层土壤有机质先增加后减小。草甸上下层土壤全磷含量在低放牧强度下显著低于中高强度。3）植被土壤变化受到自然因子和放牧活动的共同影响。高寒草甸更加耐牧，高强度放牧对高寒草原的负面影响更大，而中度放牧有利于草地尤其是高寒草原的放牧利用。4）放牧生态系统是一个环境-植物-家畜自适应系统。在放牧管理中不能仅通过控制载畜量缓解草地超载，还需要综合考虑生态系统的弹性及各营养级的适应性，合理配置放牧强度，控制季节性超载和局部超载。

Response of vegetation and soil to different grazing intensities of alpine grassland in Northern Tibet

An uneven distribution of grazing pressure in time and space leads to local land overuse and ecological degradation. However, the quantification of grazing intensity lacks direct monitoring data. It is difficult to accurately simulate the response of vegetation and soil to different grazing pressures under free grazing patterns using alternative indicators or controlled experiments. There is also a lack of research on the varying response of different grassland types with grazing intensity. In this study, a high-precision grazing trajectory dataset derived from wearable GPS locators, used for cattle and sheep, to simulate the grazing intensity, construct a grid-scale grazing spatial distribution and grazing intensity division method, and combine grassland community plot survey. Nagqu, Tibet was used as the study area. We could explore the responses and differences of vegetation and soil of alpine meadows and steppe under different grazing intensities in free grazing patterns using Duncan''s multiple comparative analysis. This study can provide new ideas for monitoring the environmental effects of grazing behavior, and put forward grazing optimization management strategies according to different grassland and local conditions; this can help with the sustainable development of traditional alpine pastoral areas. The results indicated that as the grazing intensity increased, the above-ground biomass of the steppe increased at first and then decreased, and the impact of high-intensity grazing on steppe vegetation was greater than that of the meadow. Under high grazing intensity, the soil moisture of the steppe was significantly higher than that of medium and low grazing intensity, and the bulk density of the meadow soil was significantly lower than that of the low grazing intensity, which may be because the grazing pressure was concentrated near the water source. The content of sand grains in the steppe increased with an increase in the grazing intensity. The increase in the grazing intensity led to an increase in organic matter present in the upper layer of meadow, and the organic matter of lower layer of meadow, upper and lower layer of steppe increased first and then decreased. The total phosphorus content in the upper and lower meadow soils in low grazing intensity was significantly lower than that in the medium and high intensities.Furthermore, vegetation and soil changes were affected by both natural ecological factors and the grazing activities. The alpine meadows were more tolerant to the grazing, and the high-intensity grazing had a higher negative impact on the alpine steppes; moderate grazing was conducive to the use of grassland, especially the alpine steppes. A grazing ecosystem is an environment-plant-livestock adaptive system. In grazing management, a grassland overload cannot be alleviated by only controlling the amount of livestock carried. It is also necessary to comprehensively consider the resilience of the ecosystem and the adaptability of various trophic levels, rationally configure the grazing intensity, and avoid seasonal and local overload.