摘要:围栏封育是三江源生态保护与修复主要措施之一，目前缺少基于多样地长时间序列监测数据和从植物群落结构变化角度来评估草地生态保护与修复成效的相关研究。基于多样地各经济类型群2005—2017年的地上生物量及其占总生物量比例数据，对比分析三江源草原围栏封育与放牧区植物群落结构变化差异，评价围栏封育对草地恢复的影响。研究结果表明围栏封育显著提高了地上生物量，在围栏封育期间地上生物量稳定，但群落结构出现恶化趋势，研究时段内禾本科和莎草科优良牧草生物量占比分别减少48.2%和23.9%，毒草增加了230.2%。同期放牧区禾莎草生物量占比先减少后增加，毒草杂草生物量占比先增加后减少，群落的种群结构改善可能与草畜平衡措施的实施有关。现有的持续围栏封育措施不可能但降低了草地的经济价值，也带来了一定的生态风险。因此基于草地实际产草量以及生态保护要求，确定更为合理的载畜量，实施更为精准的草畜平衡管理，应该比切断牲畜与草地关系的长期禁牧封育更为有效。



Abstract:Alpine meadow is the major vegetation type in the Three River Headwater Region (THRD) and has been suffering degradation with different degrees due to overgrazing and global warming. Fencing is adopted worldwide to protect and restore the grassland ecosystem, but there still remains uncertainty about the efficiency and the proper duration of fencing. Although many studies have concluded that the degraded grassland has been improved after grazing exclusion from the perspective of increase in the total biomass, the community structure may sometimes become poor. However, most of the present studies were conducted using limited observation with a short duration and can't represent the overall picture of community structure changes objectively. Thus, the evaluation of community structure changes based on multi-site and long-term ground monitoring is required to indicate the effect of ecological restoration measures and to take reasonable measures in the THRD. In this paper, the aboveground biomass and biomass ratio of different economic groups at 57 sites were measured to indicate the community structure changes of alpine meadow after grazing exclusion from 2005 to 2017. The aboveground biomass was measured during the peak of growing season each year and plants were sorted into six plant economic groups including gramineae, cyperaceae, edible forb, inedible forb, poisonous grass, and leguminosae. There were two main comparative analysis of aboveground biomass, between the fenced and grazed sites and between years. The results showed that fencing enhanced the total aboveground biomass but not the productivity; the biomass of gramineae and cyperaceae in the fenced sites was significantly higher and edible forbs were significantly lower than those at the grazed sites, and others had no apparent difference; the community biomass had no significant change trend either at the fenced or grazed sites; the biomass proportion of gramineae and cyperaceae decreased by 48.2% and 23.9% respectively and poisonous grass increased by 230.2% during 2005—2017 at the fenced sites. At the grazed sites, the ratio of biomass of gramineae and cyperaceae decreased first and then increased, poisonous grasses and those of forbs were opposite, and all these were related with the implementation of balance measures between grass and livestock. It can be concluded that fencing not only has no significant influence on the total aboveground biomass but even aggravates the community structure of the alpine meadow in the Three-River Headwater Region. The results indicated that long-term grazing exacerbated community structure of alpine meadow and brought about both economic and ecological risks. Therefore, compared to grazing exclusion, which cut off the relationship between livestock and grassland, a more accurate balance measures between grass and livestock should be recommended.





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