Knowledge Resource Center for Ecological Environment in Arid Area
| 中国北方植被变化及其对干旱的响应 | |
| 其他题名 | Vegetation dynamics and its response to drought in northern China |
| 徐浩杰 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 王新平 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 中国北方是国家生态环境保护规划中防沙治沙的重点区域，是关系国家生态安全的核心地区。植被是维护中国北方生态安全的屏障，发挥着防风固沙的重要作用。为了有效遏制风沙危害，自上世纪80年代起中国先后在北方干旱和半干旱区启动了“三北”防护林、退耕还林还草、京津风沙源治理等重大生态建设工程。中国北方植被动态主要受水分有效性驱动。全球变暖改变了中国北方气温和降水量的时空分布，导致热量和水分在季节之间和不同地区之间的重新分布。以干旱为代表的极端气候事件是中国北方重大的环境灾害。近几十年来中国北方的东部和中部地区干旱趋势增强，西部地区湿润趋势减弱。截止本世纪中叶，中国北方极端干旱和严重干旱的发生频率和强度可能增加。气候变化和人类活动对中国北方植被的潜在影响尚存在很大的不确定性，这种不确定性主要来源于植被响应气候平均态和极端气候的非线性、季节性和不同植物功能型之间的差异性。本文基于植被指数遥感和地面气象观测资料，采用时间趋势分析、相关分析、标准化降水蒸散指数和光能利用率过程模型，研究了1982―2014年中国北方植被活动的时间趋势及其空间差异、植被对气候平均态的响应、植被响应干旱的内在敏感性、干旱幅度对植被水分利用效率的影响，主要研究成果如下：（1）人类活动叠加在气候变化之上影响植被对气候的非线性响应。暖湿化趋势和生态建设工程促进植被改善。2000年以来水分胁迫对植被生长的负效应日益突出。（2）植被对气候响应的季节性特征反映了植物在不同的生长阶段对热量和水分的需求不同。生态系统功能对调节“植被-气候”关系发挥了重要作用。植被特性和气候背景导致不同植物功能型对气候因子的差异性响应。（3）干旱的发生存在季节性和空间差异。评估季节性干旱对植被的影响时应重点考虑夏季和冬季。水分平衡和水分利用方式决定了不同植物功能型对干旱的抵抗力。（4）植被类型、气候变化和人类活动主导了区域生态系统水分利用效率（WUE）的空间格局和时空变异性。生态系统WUE对水分有效性的差异性响应来源于不同植物功能型对干旱的响应程度和时间尺度。干旱导致的水分胁迫降低生态系统WUE。水分阈值决定了不同干旱等级对生态系统WUE的影响。本研究揭示了植被对气候变化和人类活动的非线性响应、植被变化的季节性差异及其来源、植被对干旱响应的内在敏感性差异、生态系统水分利用效率响应干旱的阈值效应，对中国北方生态环境建设和生态成效评价具有重要的现实意义，可提高动态全球植被模型预测未来干旱生态系统潜在变化的能力。 |
| 英文摘要 | According to the plan on eco-environment improvements for the period of 2016-2020, more attention should be paid to the prevention and control of sandy desertification in northern China, which has an important effect on the national ecological security. The vegetation acts as an eco-security shield and plays an important role in windbreak and sand fixation. To reduce and combat the hazards of sandstorms, the Chinese government has launched ecological restoration projects in arid and semi-arid lands since the 1980s, including the Three-North Shelter Forest Program, the Grain for Green Program and the Beijing-Tianjin Sandstorm Source Control Program. Vegetation dynamics is primarily driven by water availability. Global warming alters the spatiotemporal patterns of temperature and precipitation, leading to heat and moisture redistribution across seasons and regions. Drought is one of the major environmental disasters in northern China. Drought trends have been detected in the eastern and central portion of the region, and the wetting tendency in western region has weakened in recent decades. The frequency and magnitude of extreme and severe drought may increase by the middle of the 21st century. However, climatic and anthropogenic impacts on the vegetation in northern China are uncertain. The reason for this uncertainty lies in the fact that the vegetation response to climate mean/extremes shows nonlinearity, seasonality and differences among plant functional types.Based on remotely sensed vegetation index and in-situ meteorological data for the years 1982–2014, in conjunction with the trend and correlation analysis methods, the standardized precipitation evapotranspiration index and the ecological process Carnegie–Ames–Stanford Approach model, we analyzed: 1) vegetation growth trend across seasons and regions; 2) vegetation response to climate variables at biome and pixel scales; 3) intrinsic drought sensitivity of vegetation; 4) the impact of drought severity on ecosystem water use efficiency. The main conclusions were as follows.(1) Human activities superimposed on climate change, causing the nonlinear response of vegetation to climate. The warm-wet tendency and the ecological construction project accelerated plant growth. The negative effect of water stress on vegetation growth has become increasingly prominent since 2000.(2) The climate drivers for vegetation growth varied across different seasons, indicating differences in the demand of vegetation for heat and moisture at different stages throughout the year. Ecosystem functions regulated the relationships between vegetation and climate. Diverse responses of different vegetation types to climate variables were related to vegetation characteristics and climatic conditions.(3) Seasonal and spatial differences existed in the occurrence of drought. It was important to consider summer and winter when evaluating the effects of seasonal drought on vegetation. Drought resistance varied in different vegetation types due to water balance and water use strategies.(4) Vegetation types, climate change and human activities controlled the spatial pattern and spatiotemporal variability of water use efficiency (WUE) at ecosystem scales. Diverse responses of WUE to water availability were related to the sensitivity and time-scales at which different vegetation types responded to drought. Drought decreased water availability, and hence WUE. Water threshold determined the impact of drought severity on WUE.Our research highlighted the nonlinear responses of vegetation to climate and anthropogenic activities, and the seasonal characteristics of vegetation response to climate variables. Also, we revealed intrinsic drought sensitivity of vegetation and threshold effect of WUE in response to drought at ecosystem scales. These results have important implications for eco-environment construction and ecological effect evaluation. Our study could be further extended to improve the performance of the Dynamic Global Vegetation Model to predict how dryland ecosystems respond to climate mean/extremes under future scenarios of climate change. |
| 中文关键词 | 干旱生态系统 ; 非线性 ; 季节性 ; 植物功能型 ; 水分利用效率 |
| 英文关键词 | dryland ecosystems nonlinearity seasonality plant functional types water use efficiency |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生态学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287974 |
| 推荐引用方式 GB/T 7714 | 徐浩杰. 中国北方植被变化及其对干旱的响应[D]. 中国科学院大学,2017. |
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