Knowledge Resource Center for Ecological Environment in Arid Area
| 放牧对干旱区草地蒸散发和生物量的影响研究 | |
| 其他题名 | Effects of grazing on evapotranspiration and biomass of grassland in arid area |
| 黄小涛 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 导师 | 罗格平 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 草地生态系统具有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-BGC grazing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。 |
| 英文摘要 | Grassland ecosystems serve important economic and ecological functions, such as material production, climate regulation, soil and water conservation, sand stabilization, soil improvement and biodiversity preservation. Grassland ecosystems are widely distributed in arid area. However, grassland ecosystems are easily susceptible to disturbances and highly vulnerable to climate change and human activities due to lack of water resources in arid area. Grazing is the most important human disturbances on grassland ecosystems for thousands of years. In recent decades, grazing intensity has increased significantly. Overgrazing, which distinctly decreases grassland productivity, has become a widespread activity that has led to severe degradation of grassland ecosystems. Animal husbandry is an important economic pillar industry in arid area. And the research regarding the effect of grazing on grassland ecosystem is very important to the healthy development of economy and ecological environment in arid area. The response mechanism of grassland ecosystem to grazing has been a hot and difficult topic in grassland ecology research. Grassland evapotranspiration and biomass are two key components of grassland construction. And the effect of grazing on grassland evapotranspiration and biomass is an important scientific problem in the field of grassland ecology at present. Previous studies based on sites showed that grazing reduced grassland evapotranspiration. However, a comparative analysis of the evapotranspiration between ungrazing and grazing scienarios has not been conducted at regional scale, which is detrimental to the overall understanding of the grazing effects on grassland evapotranspiration. In addition, many studies on the effects of grazing on grassland biomass dynamics were conducted. However, there were different conclusions due to the differences in grassland type and research method. Thus, experts and scholars at home and abroad have disputes over whether moderate grazing promotes plant growth.The northern Tianshan Mountains, Xinjiang and Central Asia are the arid areas at different scale. Grassland ecosystems are widely distributed in these areas. And there are distinct differences in landform, climate, grassland type, grazing intensity and system. Such areas are the ideal representative areas for the research regarding grazing effects on various grassland ecosystems in arid areas. The study selected three different spatial scales of grassland ecosystems, including northern Tianshan Mountain, Xinjiang and Central Asia, as the study areas to conduct the research. Firstly, the modified BIOME-BGC Grazing model was calibrated and validated based on field observation data in different grassland ecosystems of the arid area. Secondly, effects of grazing on evapotranspiration and biomass were estimated and analysized_based on different scenatio simulations in accordance with regions, grassland types and grazing managements using the modified Biome-BGC Grazing model. Specific method steps include: (1) the physiological and ecological indexes, structure and functional characteristics of the main grassland ecosystems in the study area were analyzed based on field observation. (2) the BIOME-BGC grazing model was calibrated and validated based on field observation data. In addition, the hypothesis was validated that "moderate grazing can improve the primary productivity of grassland ecosystem under water stress" based on field observation data. (3) the effects of grazing on evapotranspiration and biomass were estimated and analysized based 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 grassland evapotranspiration and biomass in arid area using the BIOME-BGC grazing model.2) The viewpoint that moderate grazing can improve primary productivity of grassland under water stress was validated using experimental observation data acquired by mowing simulated grazing in the low-mountain typical grassland of Yongfeng Township, Urumqi, from 2013 to 2017. The preliminary conclusion that the aboveground biomass of grassland ecosystems which were not under water stress was often decreased under the grazing scenarios was drawn from the experimental observation data through mowing simulated grazing in the Mid-mountain Meadow in Urumqi, Xinjiang.3) In general, grazing decreased grassland net primary productivity (NPP). And the difference in NPP between grazing and ungrazed scenarios showed an increasing trend due to increased grazing intensities in the past. NPP under the ungrazed scenario showed an increasing trend while NPP under the grazing scenario showed an decreasing trend. And there was distinct spatial difference in NPP between grazing and ungrazed scenarios. NPP under the grazing scenario decreased in most regions. NPP decrease was mainly distributed 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 ET between grazing and ungrazed scenarios showed an increasing trend due to increased grazing intensities in the past. ET under grazing and ungrazed scienarios increased. However, ET increase was more obvious under the ungrazed scenario than under the grazing scenario. And there was distinct spatial 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 WUE between grazing and ungrazed scenarios showed an increasing trend due to increased grazing intensities in the past. In addition, an obvious fluctuating decline in WUE was observed under the grazing scenario, whereas no significant fluctuating decline was observed under the ungrazed scenario. And there was distinct spatial difference in WUE between grazing and ungrazed 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% of Central Asia grassland potential net primary production (NPPo) and HANPP efficiency was 70.34% in this region. Interannual variations in HANPP and HANPP as a percentage of NPPo (HANPP%NPPo) were significantly positively related to grazing intensity (P < 0.01). Interannual variation in HANPP efficiency was negatively related to grazing intensity (P < 0.1). HANPP showed strong regional variation. High HANPP values were mainly observed in temperate grassland and some forest meadow. Low HANPP values were mainly observed in desert grassland and some forest meadow. The spatial pattern of HANPP%NPPo was similar to that of HANPP in this region. Interannual variations in HANPP were mainly determined by population change and economic development. Spatial patterns of HANPP were primarily determined by grazing intensity and grazing system.In this study, grazing effects on ET and biomass was estimated and analysed in arid area using Biome-BGC grazing model. Different scenarios were evaluated using model estimates to distinguish between “grazed” and “ungrazed” scenarios and to compare among studies conducted in the same area, allowing grazing effects to be effectively evaluated. The findings will help to understand the driving mechanism of grazing management on the dynamic of water and carbon of grassland ecosystems in arid areas, and also have important practical significance for grazing management of grassland ecosystems in arid areas.However, there are several problems in the thesis: (1) The grazing process was simplified in Biome-BGC grazing model. Many assumptions about the ideal conditions of the grazing process in the model may be inconsistent with the actual situation. For example, in Biome-BGC grazing model, we did not distinguish between the edible species of vegetation and the trampling effect of grazing was also not effectively considered. (2) It was difficult to conduct precise parameterization of some physiological and ecological parameters involving community in the model because the corresponding experimental research is relatively few. (3) The changes in grassland range caused by other human activities such as land reclamation was not considered 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 impact of livestock trampling. (2) strengthen field experiments and establish a long-term positioning observation station to collect more physiological and ecological parameters of vegetation in Central Asia. Doing all these will provide solid data support for further research. |
| 中文关键词 | 干旱区 ; 草地生态系统 ; 放牧 ; 生物量 ; 蒸散发 |
| 英文关键词 | arid area grassland ecosystem grazing biomass evapotranspiration |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 地图学与地理信息系统 |
| 来源机构 | 中国科学院新疆生态与地理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288158 |
| 推荐引用方式 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]. 中国科学院大学,2018. |
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