封育对三江源退化草甸关键生态功能恢复的影响及封育年限的优化

The degradation of grassland causes the decline of ecological function and enclosure can restore the degraded grassland. However, it is still not clear that the evolution rule and the coupling relationship between ecological parameters and the duration of enclosure, as well as the appropriate enclosure duration when the ecological function restored. This study will conduct three paired experiment of enclosure and grazing sample areas along different degradation stages on the degraded alpine meadow in Three-River Headwater Regions. The ecological parameters of micrometeorology, vegetation community structure and productivity, soil/vegetation carbon and water conservation and soil water holding will be compared. Then the coupling relationship and evolution rule between the key ecological parameters along the years of enclosure will be analyzed. The response degree of ecological parameters to the years of enclosure will be explored by the regression variance interpretation power. The contribution of the enclosure and climatic factors to ecological recovery will be revealed by principal component eigenvalues. Secondly, according to the spatial survey of the enclosure duration, we will establish the response characteristic curve of the key ecological parameters and the enclosure durations and propose the appropriate duration for the rehabilitation. Combining the response degree and the synergistic evolution between the key ecological parameters and the years of enclosure, we will make the appropriate enclosure duration that ecological function recovery along different degradation gradient of alpine meadow in Three-River Headwater Region. The results can provide a theoretical basis and observational data for restoring and governing of degraded grassland.

草地退化引起生态功能衰减。封育可使退化的植被得到恢复。但恢复过程中生态参数随封育恢复年限遵循怎样的演变规律和协同关系，生态功能达最佳时的封育年限等仍不清楚。本研究拟在三江源退化的高寒草甸，设置3处不同退化阶段的封育与未封育实验样地。对比微气象、植被群落结构与生产力、土壤/植被碳水储量、持水量等生态参数的观测。分析植物多样性与生产力、植被/土壤碳水固持等关键生态参数随封育年限的差异响应、协同关系及演变规律。利用回归方差解释率明晰生态参数对封育年限的响应程度，基于主成分特征值揭示封育和生态因子对生态参数恢复中的贡献率。联系不同时期封育样地的空间调查，构建关键生态参数与恢复年限的响应特征曲线，确立其康复的适宜封育年限。结合各关键生态参数对封育年限响应程度、协同演变规律以及权重贡献分析，提出三江源退化高寒草甸综合生态功能达最佳时封育恢复年限的优化方案。为退化草地恢复与治理提供理论依据和数据支撑。

在果洛州玛沁县设置了原生植被、轻度退化、中度退化、重度退化、极度退化等5个不同退化程度的高寒草甸围栏封育试验样地，并结合三江源区域退化高寒草甸典型恢复措施（季节休牧、长短期围栏封育、人工建植）的区域调查，开展了植被群落及土壤性状的变化研究，以期揭示高寒草甸退化及恢复中主要生态功能的响应规律，并综合评价典型恢复措施。在退化过程中，群落盖度、Shannon-wiener指数、Simpson指数、Pielou 指数、地上（下）生物量均表现为降低的趋势，禾草类、莎草类的生存状态降低、杂类草的生存状态增加，土壤呼吸速率下降。围栏封育后，各退化样地的群落高度增加，但轻度退化样地的植被覆盖度反而降低。各退化样地的群落优势种由杂类草向禾草类过渡，Shannon-wiener指数、Simpson指数、Pielou指数增加。草地质量综合评价表明，夏季休牧样地草地质量得分随恢复时期的延长逐渐增高，恢复末期的草地质量评分最好；短期围封 1 年后的样地草地质量得分均优于围封前的对应样地；恢复 11 年后的人工建植样地的恢复效果优于围栏封育措施。对不同围栏封育年限（0-54年）下高寒草甸植被和土壤固碳持水能力变化的研究显示，退化草甸土壤有机质和饱和持水量的恢复年限分别需要 5.4年和 12.4 年，地上生物量在第 12 年达到最大。依据专家打分法确定指标权重，计算得到围栏封育的最佳恢复年限约为 9 年。基于机器学习算法的结果表明，气候因素（76.7%）对青海草地地上生物量时空变化的贡献率远大于围封封育（13.7%）。围封能显著提高高寒草地地上生物量，但不同草地类型对围封封育的响应不同，围封对高寒草甸地上生物量的提升幅度和贡献率最高，其次是高寒草原，温性草原最低。因此，退化高寒草甸植被盖度、生物量、物种多样性降低，物种由禾草、莎草过渡到杂类草。围栏封育后，退化高寒草甸的植被高度、物种多样性均增加，短期封育后的轻度、中度退化草甸的植被恢复效果比较明显，长期封育最佳年限为8-10年，围栏封育对高寒草甸地上生物量时空变异的影响较大但小于气候因素。