小尺度高寒湿地放牧干扰格局——以纳帕海湿地为例

高寒湿地放牧干扰强烈,是其生态系统退化的主因。湿地植被生物量空间格局不仅能够反映自然因素的作用,也能够体现地域放牧等人类活动的主要特征,因此常作为表征放牧干扰格局的主要度量方法。但尺度效应导致的植被生物量影响要素在不同空间尺度下存在较大差异,尤其是针对面积为几十至几百km²范围的小尺度高寒湿地而言,自然因素和放牧等人为干扰对其植被地上生物量的共同作用特征仍不明确,缺乏针对该类型湿地的合理评估模式。以滇西北国际重要湿地纳帕海为例,在排除其它人为干扰的条件下,通过植被地上生物量的空间异质性特征来表征其放牧干扰格局,并以该案例为基础提出一种小尺度高寒湿地放牧干扰格局评估模式。研究尝试基于详细地面植被调查,获得潜在植被地上生物量,利用调查同时期高分定量遥感方法(法国PLEIADES卫星数据结合实测植被地上生物量建模)获得实际植被地上生物量,并使用潜在与实际植被地上生物量之差的空间异质性特征表示纳帕海湿地放牧干扰格局。该评估模式可以有效减少对于小尺度湿地放牧干扰数据的依赖,同时减少牛羊马等大牲畜散养带来的空间分布随机性。研究结果显示纳帕海湿地放牧干扰对湿地植被地上生物量的影响严重,影响比例约为93.5%。研究发现水文等自然因素和放牧等人为干扰分别决定纳帕海湿地植被地上生物量的上限和下限,并基于此提出四方面干扰调控策略。

Disturbance pattern of grazing in fine-scale alpine wetland: a case study of Napahai, an internationally important wetland

Alpine wetland has strong grazing disturbance, which is the main cause of ecosystem degradation. The spatial pattern of wetland vegetation biomass can not only reflect the role of natural factors, but also reflect the main characteristics of human activities such as regional grazing. So it is often used as the main measurement method to characterize the pattern of grazing disturbance. However, the factors affecting vegetation biomass caused by scale effect differ greatly at different spatial scales. Especially for fine-scale alpine wetlands with an area ranging from tens to hundreds of km², the characteristics of the combined effects of natural factors and human disturbance such as grazing on the above-ground vegetation biomass are still unclear, and there is a lack of reasonable evaluation model for this type of wetland. This study took Napahai wetland, a Ramsar site in northwestern Yunnan, as an example, and characterized its grazing disturbance pattern through the spatial heterogeneity characteristics of above-ground vegetation biomass under the condition of excluding other human disturbances. We also proposed an evaluation model of grazing pattern in fine-scale alpine wetlands based on this case. The study attempted to obtain the aboveground biomass of potential vegetation based on a detailed ground vegetation survey and to obtain the actual aboveground biomass of vegetation by using a high-resolution quantitative remote sensing method (French PLEIADES satellite data combined with measured vegetation aboveground biomass modeling) during the same period of investigation. Then we used the spatial heterogeneity characteristic of the difference between potential and actual vegetation above-ground biomass to represent the Napahai wetland grazing disturbance patterns. The evaluation model can effectively reduce the dependence on fine-scale wetland grazing interference data, and reduce the randomness of spatial distribution caused by large livestock such as cattle, sheep, and horses. The results showed that the grazing disturbance seriously affected the aboveground biomass of wetland vegetation, and the impact ratio was about 93.5%. The study also found that the natural factors such as hydrology and anthropogenic disturbances such as grazing determine the upper and lower limits of above-ground biomass of vegetation in Napahai Wetland, respectively, and put forward four aspects of interference control strategies based on the research results.