EGI OpenIR  > 研究系统  > 荒漠环境研究室
放牧对干旱区草地蒸散发和生物量的影响研究
黄小涛
Subtype博士
Thesis Advisor罗格平
2018-06-05
Degree Grantor中国科学院大学
Place of Conferral新疆乌鲁木齐
Degree Discipline理学博士
Keyword干旱区 草地生态系统 放牧 生物量 蒸散发 Biome-BGC grazing模型 arid area grassland ecosystem grazing biomass evapotranspiration Biome-BGC grazing model
Abstract草地生态系统具有重要的经济和生态价值,诸如畜牧业生产、防风固沙、保持水土、改良土壤和生物基因保持等。干旱区草地广泛分布,同时因水资源短缺而生态脆弱,对气候变化和人类活动非常敏感。放牧是几千年来人类对其最主要的干扰活动。近几十年来干旱区放牧强度日益提高,过度放牧引起的草地退化现象日益严重。畜牧业是干旱区重要的经济支柱产业,研究放牧对草地生态系统的影响对干旱区经济与生态环境的健康发展至关重要。草地生态系统对放牧的响应机理也一直是草地生态学研究的热点和难点。草地蒸散发和生物量是草地建设的两个关键分量,放牧对草地蒸散发和生物量的影响研究是目前草地生态学领域的重要科学问题。目前站点研究表明放牧会降低草地蒸散发,但缺乏区域尺度的放牧与不放牧情景的蒸散发对比分析,这非常不利于全面深入的认识草地蒸散发对放牧的响应机理。另外,有关草地生物量动态对放牧响应机理的研究,因不同草地的具体情况或采用研究方法的差异会有不同结论。目前国内外专家学者对“适度放牧是否促进牧草生长”存在争议。天山北坡、新疆、中亚属于不同尺度的干旱区,草地生态系统分布广泛,且不同区域地形、气候、草地类型和放牧强度与制度差异显著,是研究不同放牧管理对干旱区不同类型草地影响的理想代表区域。本研究选择天山北坡、新疆、中亚三个不同空间尺度的草地生态系统为研究对象,首先基于不同草地的野外观测数据对已有的 Biome-BGC grazing 放牧模型进行校验,然后针对不同区域、不同草地类型和不同程度的放牧干扰,基于校验后的 Biome-BGC grazing 放牧模型,通过情景模拟综合评价放牧对干旱区草地生态系统蒸散发和生物量动态的影响。具体方法步骤包括:1)基于野外试验观测,揭示研究区主要草地生态系统生理生态指标、结构与功能特征;2)基于野外观测数据,对 Biome-BGC grazing 放牧模型进行校验,并基于野外观测数据,验证“适度放牧有助于提高受水分胁迫的草地生态系统的初级生产力”的假设是否成立;3)基于校验后的 Biome-BGCgrazing 放牧模型,通过情景模拟分析放牧对干旱区草地生态系统蒸散发与生物量的影响。结果表明:1) 利用 BIOME-BGC grazing 模型模拟放牧对干旱区草地生态系统蒸散发与生物量动态影响的研究是可行的。2) 利用 2013-2017 年乌鲁木齐永丰乡低山丘陵典型草原刈割模拟放牧的实验观测数据,验证了“适度放牧可提高受水分胁迫草地的初级生产力”的观点。利用乌鲁木齐菊花台中山草甸刈割模拟放牧的实验观测得出初步结论:在放牧情景下,不受水分胁迫的草地地上生物量往往是降低的。3) 总体上,放牧降低了草地净初级生产力,且随着放牧强度的增大,放牧情景与不放牧情景的草地净初级生产力差异是呈增加趋势的。在不放牧情景下,NPP 呈增加趋势,在放牧情景下 NPP 呈降低趋势。同时放牧情景与不放牧情景的草地净初级生产力存在显著的空间异质性。放牧情景下,NPP 显著降低的区域主要分布在放牧强度较大的区域,少部分区域因适度放牧出现了 NPP 的增加。4) 总体上,放牧降低了草地蒸散发,且随着放牧强度的增大,放牧情景与不放牧情景的草地蒸散发的差异是呈增加趋势的。放牧与不放牧情景下蒸散发均呈增加趋势,但放牧情景下蒸散较不放牧情景缓慢。同时放牧情景与不放牧情景草地蒸散发的差异存在显著的空间异质性。总体上,放牧情景下,在放牧强度较大的山地区域蒸散发降低较为显著。5) 总体上,放牧降低了草地水分利用效率,且随着放牧强度的增大,放牧情景与不放牧情景的草地水分利用效率的差异是呈增加趋势的。在放牧情景下水分利用效率是呈下降趋势的,而在不放牧情景下,水分利用效率没有明显的下降趋势。同时放牧情景与不放牧情景的草地水分利用效率的差异存在显著的空间异质性。放牧情景下,草地水分利用效率显著降低的区域主要分布在放牧强度较大的区域。6)中亚草地人类占用净初级生产力(HANPP)为 47.08 g C/m2/yr,占整个中亚草地潜在净初级生产力的 34.08%,中亚草地人类占用净初级生产力效率(HANPP efficiency)为 70.34%。 HANPP 及 HANPP 占潜在 NPP的比重 (HANPP%NPPo)的年际变化均与放牧强度的年际变化显著正相关(P < 0.01)。HANPP efficiency 的年际变化与放牧强度的年际变化负相关 (P < 0.1)。中亚草地 HANPP 区域差异显著。高 HANPP 值主要分布在温带草原和部分森林草甸。低 HANPP 值主要分布在荒漠草原和部分森林草甸。中亚草地 HANPP%NPPo的空间格局与 HANPP 的空间格局相似。中亚草地 HANPP 的年际变化主要受人口变化和经济发展两大因素的影响。中亚草地 HANPP 空间格局主要受放牧强度和放牧制度决定。本研究基于 Biome-BGC grazing 模型,通过区域尺度放牧情景与不放牧情景的模拟对比分析了放牧管理对干旱区不同草地类型的蒸散发及生物量等的影响。研究结果将有助于理解放牧管理对干旱区草地生态系统水碳动态变化的驱动机理,同时对干旱区草地生态系统的放牧管理具有重要现实意义。但是,论文还存在几方面的问题:1)放牧模型中对放牧过程进行了简化,许多关于放牧过程理想条件的假设可能与实际情况不符。例如在放牧模型中,我们未对植被物种的可食性进行区分、未考虑放牧的践踏效应等;2)由于相应实验研究也比较少,较难精确化模型中涉及群落的一些生理生态参数;3)未考虑土地开垦等其它人类活动引起的草地范围的变化。鉴于以上问题,该研究未来的工作重心可以放在以下几个方面:(1)深化 Biome-BGC grazing 草地生态系统放牧模型的放牧过程,如考虑牲畜践踏的影响;(2)加强野外实验,建立长期定位观测站,更多的搜集中亚植被的生理生态参数,为进一步研究提供坚实的数据支撑。
Other AbstractGrassland ecosystems serve important economic and ecological functions, suchas material production, climate regulation, soil and water conservation, sandstabilization, soil improvement and biodiversity preservation. Grassland ecosystemsare widely distributed in arid area. However, grassland ecosystems are easilysusceptible to disturbances and highly vulnerable to climate change and humanactivities due to lack of water resources in arid area. Grazing is the most importanthuman disturbances on grassland ecosystems for thousands of years. In recent decades,grazing intensity has increased significantly. Overgrazing, which distinctly decreasesgrassland productivity, has become a widespread activity that has led to severedegradation of grassland ecosystems. Animal husbandry is an important economicpillar industry in arid area. And the research regarding the effect of grazing ongrassland ecosystem is very important to the healthy development of economy andecological environment in arid area. The response mechanism of grassland ecosystemto grazing has been a hot and difficult topic in grassland ecology research. Grasslandevapotranspiration and biomass are two key components of grassland construction.And the effect of grazing on grassland evapotranspiration and biomass is an importantscientific problem in the field of grassland ecology at present. Previous studies basedon sites showed that grazing reduced grassland evapotranspiration. However, acomparative analysis of the evapotranspiration between ungrazing and grazingscienarios has not been conducted at regional scale, which is detrimental to the overallunderstanding of the grazing effects on grassland evapotranspiration. In addition,many studies on the effects of grazing on grassland biomass dynamics wereconducted. However, there were different conclusions due to the differences ingrassland type and research method. Thus, experts and scholars at home and abroadhave disputes over whether moderate grazing promotes plant growth.The northern Tianshan Mountains, Xinjiang and Central Asia are the arid areas atdifferent scale. Grassland ecosystems are widely distributed in these areas. And thereare distinct differences in landform, climate, grassland type, grazing intensity andsystem. Such areas are the ideal representative areas for the research regardinggrazing effects on various grassland ecosystems in arid areas. The study selected threedifferent spatial scales of grassland ecosystems, including northern TianshanMountain, Xinjiang and Central Asia, as the study areas to conduct the research. Firstly, the modified BIOME-BGC Grazing model was calibrated and validated basedon field observation data in different grassland ecosystems of the arid area. Secondly,effects of grazing on evapotranspiration and biomass were estimated andanalysized_based on different scenatio simulations in accordance with regions,grassland types and grazing managements using the modified Biome-BGC Grazingmodel. Specific method steps include: (1) the physiological and ecological indexes,structure and functional characteristics of the main grassland ecosystems in the studyarea were analyzed based on field observation. (2) the BIOME-BGC grazing modelwas calibrated and validated based on field observation data. In addition, thehypothesis was validated that "moderate grazing can improve the primary productivityof grassland ecosystem under water stress" based on field observation data. (3) theeffects of grazing on evapotranspiration and biomass were estimated and analysizedbased on scenario simulations in arid area using BIOME-BGC grazing model.The results were showed as follows:1) It is possible that simulating the effects of grazing on grasslandevapotranspiration and biomass in arid area using the BIOME-BGC grazingmodel.2) The viewpoint that moderate grazing can improve primary productivity ofgrassland under water stress was validated using experimental observationdata acquired by mowing simulated grazing in the low-mountain typicalgrassland of Yongfeng Township, Urumqi, from 2013 to 2017. Thepreliminary conclusion that the aboveground biomass of grasslandecosystems which were not under water stress was often decreased under thegrazing scenarios was drawn from the experimental observation data throughmowing simulated grazing in the Mid-mountain Meadow in Urumqi,Xinjiang.3) In general, grazing decreased grassland net primary productivity (NPP). Andthe difference in NPP between grazing and ungrazed scenarios showed anincreasing trend due to increased grazing intensities in the past. NPP underthe ungrazed scenario showed an increasing trend while NPP under thegrazing scenario showed an decreasing trend. And there was distinct spatialdifference in NPP between grazing and ungrazed scenarios. NPP under thegrazing scenario decreased in most regions. NPP decrease was mainlydistributed in the regions with high grazing intensity. In rare case, NPP increased due to moderate grazing.4) In general, grazing decreased grassland ET. And the difference in ETbetween grazing and ungrazed scenarios showed an increasing trend due toincreased grazing intensities in the past. ET under grazing and ungrazedscienarios increased. However, ET increase was more obvious under theungrazed scenario than under the grazing scenario. And there was distinctspatial difference in ET between grazing and ungrazed scenarios. Generally,ET decrease was more obvious in mountainous areas than in plain areas.5) In general, grazing decreased grassland WUE. And the difference in WUEbetween grazing and ungrazed scenarios showed an increasing trend due toincreased grazing intensities in the past. In addition, an obvious fluctuatingdecline in WUE was observed under the grazing scenario, whereas nosignificant fluctuating decline was observed under the ungrazed scenario.And there was distinct spatial difference in WUE between grazing andungrazed scenarios. Generally, WUE decrease was relatively obvious in the r6) Our estimates showed that HANPP was 47.08 g C/m2/yr, which represented 34.08% ofCentral Asia grassland potential net primary production (NPPo) and HANPP efficiencywas 70.34% in this region. Interannual variations in HANPP and HANPP as apercentage of NPPo (HANPP%NPPo) were significantly positively related to grazingintensity (P < 0.01). Interannual variation in HANPP efficiency was negatively related tograzing intensity (P < 0.1). HANPP showed strong regional variation. High HANPPvalues were mainly observed in temperate grassland and some forest meadow. LowHANPP values were mainly observed in desert grassland and some forest meadow. Thespatial pattern of HANPP%NPPo was similar to that of HANPP in this region.Interannual variations in HANPP were mainly determined by population change andeconomic development. Spatial patterns of HANPP were primarily determined bygrazing intensity and grazing system.In this study, grazing effects on ET and biomass was estimated and analysed inarid area using Biome-BGC grazing model. Different scenarios were evaluated usingmodel estimates to distinguish between “grazed” and “ungrazed” scenarios and tocompare among studies conducted in the same area, allowing grazing effects to beeffectively evaluated. The findings will help to understand the driving mechanism ofgrazing management on the dynamic of water and carbon of grassland ecosystems inarid areas, and also have important practical significance for grazing management ofgrassland ecosystems in arid areas.However, there are several problems in the thesis: (1) The grazing process wassimplified in Biome-BGC grazing model. Many assumptions about the idealconditions of the grazing process in the model may be inconsistent with the actualsituation. For example, in Biome-BGC grazing model, we did not distinguish betweenthe edible species of vegetation and the trampling effect of grazing was also noteffectively considered. (2) It was difficult to conduct precise parameterization of somephysiological and ecological parameters involving community in the model becausethe corresponding experimental research is relatively few. (3) The changes ingrassland range caused by other human activities such as land reclamation was notconsidered in this study.In view of the above, the future study can be focused on the following aspects: (1)improve grazing process in the Biome-BGC grazing model by considering the impactof livestock trampling. (2) strengthen field experiments and establish a long-termpositioning observation station to collect more physiological and ecologicalparameters of vegetation in Central Asia. Doing all these will provide solid datasupport for further research.
Subject Area地图学与地理信息系统
Language中文
Document Type学位论文
Identifierhttp://ir.xjlas.org/handle/365004/14927
Collection研究系统_荒漠环境研究室
Affiliation中国科学院新疆生态与地理研究所
First Author Affilication中国科学院新疆生态与地理研究所
Recommended Citation
GB/T 7714
黄小涛. 放牧对干旱区草地蒸散发和生物量的影响研究[D]. 新疆乌鲁木齐. 中国科学院大学,2018.
Files in This Item:
There are no files associated with this item.
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Google Scholar
Similar articles in Google Scholar
[黄小涛]'s Articles
Baidu academic
Similar articles in Baidu academic
[黄小涛]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[黄小涛]'s Articles
Terms of Use
No data!
Social Bookmark/Share
All comments (0)
No comment.
 

Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.