京津风沙源治理工程不同恢复措施对草地恢复过程的差异性影响

中国北方草原区域作为我国北方重要的防沙治沙生态屏障,长期以来大规模投入实施了系列生态恢复工程。为了解不同恢复措施对草地恢复的影响异同,以京津风沙源治理工程的草原治理区域为研究对象,采用工程区内外对比法探索4种典型工程恢复措施及措施组合(围封禁牧、补播草种、小流域治理和基本草牧场建设)对草地群落物种组成、生产力构成和物种多样性的差异性影响。结果显示:1)各工程恢复措施均趋向增加群落的高度和盖度,其中围封禁牧草地的恢复最为明显;群落中禾本科、莎草科物种重要值增加,杂类草下降,群落建群种由克氏针茅、糙隐子草、百里香等较低矮物种转变为大针茅、羊草、羽茅等较高大的多年生禾草;2)各恢复措施均显著增加群落的地上生物量(P<0.05),但种植人工饲草的基本草牧场地下生物量显著下降,使得群落总生物量也显著减少(49%);只有围封禁牧措施使群落总生物量、地下生物量和地上生物量均显著增加;群落内C₃植物、多年生植物生物量比例趋向增加; 3)各工程恢复措施均未显著增加群落内物种丰富度,却均趋向减少群落物种均匀度,补播草种和基本草牧场建设区域Shannon-Wiener多样性指数下降达到显著水平。以上结果表明长期的恢复措施实施能明显恢复草地的植被覆盖和地上生产力水平,提高草地的饲草品质,有助于区域沙源固定、碳汇增加和饲草供应恢复,但长期的工程干预有可能对区域的植物群落物种多样性水平存在负面影响。

The effects of different restoration practices on temperate grassland ecosystems in the Beijing-Tianjin Sand Source Control Project

The grasslands of Northern China are an important ecological barrier preventing and controlling desertification;there has been a long history of large ecological restoration projects in this area.In order to understand the impacts of various restoration projects on species composition,productivity and species diversity of grassland communities,this study focused on the grasslands of the Beijing-Tianjin Sand Source Control Project,evaluating the effects of four typical restoration practices and their combinations:Fencing to exclude grazing animals,over sowing,small watershed conservation and basic ranch by comparing areas in and out of the Project area and discusses the driving mechanism of any differences.All of the engineering based restoration measures tended to increase the height and cover of communities;the restoration of grazing excluded steppe provided the best example of this.The prevalence of species from Gramineae and Cyperaceae increased while weeds decreased.The constructive species of communities changed from shorter species such as Stipa sareptana var.krylovii,Cleistogenes squarrosa and Thymus serpyllum to taller perennial Poaceae species such as Stipa grandis,Leymus chinensis and Achnatherum sibiricum.All of the engineered restoration measures tended to increase the above-ground biomass but below-ground biomass in typically management areas planted with artificial fodder decreased significantly,which led to a significant drop in overall community biomass;the overall biomass,above-ground biomass and below-ground biomass increased significantly where grazing was excluded.The ratio of the biomass of C3 plants and perennial plants tended to increase.None of the engineered restoration measures increased the abundance of species in communities but all tended to decrease the evenness of species;the Shannon-Wiener index in supplementary grass planted and typical grazed areas decreased significantly.The results showed that long-term engineering measures restored the vegetation cover and productivity of grassland and increased fodder quality which helped stabilize sand,increased carbon sequestration fodder availability.However,engineering intervention may result in reduced species diversity of vegetation communities in a long term.