Knowledge Resource Center for Ecological Environment in Arid Area
| 青藏高原多年冻土区植被生长和分布 | |
| 其他题名 | The growth and distribution of vegetation in present situation and its changes in future for the permafrost regions of the Qinghai-Tibet Plateau |
| 王志伟 | |
| 出版年 | 2015 |
| 学位类型 | 博士 |
| 导师 | 赵林 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 青藏高原是一个经历了长期复杂地质作用过程的多阶段拼合体，拥有世界上最大面积的高海拔区域，被公认为“世界第三极”，具有独特的自然地貌单元，对气候变化敏感又属于生态脆弱带。随着近百年来全球气温逐年升高，广泛分布于青藏高原的多年冻土也存在严重的退化现象，而且根据现有研究表明这种趋势在21世纪仍将持续。多年冻土的退化，会导致位于其上的活动层厚度增加，进而改变土壤中的水、热环境，对青藏高原多年冻土区的植被生长和分布存在重要的影响作用。当该区域植被和土壤水、热状况发生变化时，又会通过下垫面对大气圈底部的环境产生反作用，进而影响到周边地区乃至全球的气候变化。同时，青藏高原多年冻土区的植被生长和分布发生改变时，又会通过自身生物量的增减影响到该区域的土壤有机碳含量，以至改变该区域碳的源汇效应。因此，研究青藏高原多年冻土区植被的生长和分布现状及其变化意义重大，不仅可以为研究气候变化提供理论支撑，还可以为青藏高原多年冻土区乃至全球的碳循环过程提供关键的数据基础。 基于此，本文首先利用GIMMS NDVI产品分析了1982年到2012年全球植被的平均值和变化趋势，发现青藏高原地区无论是在NDVI平均值方面，还是在31年的变化率上都有相对较小的数值，甚至与同样拥有大面积多年冻土的环北极地区相比，数值也较小。所以，相比全球其它区域，青藏高原地区的植被相对比较稀疏，生态环境也更加脆弱。之后，利用青藏高原多年冻土区2009年9月到2013年9月的植被观测资料和遥感数据完成该地区小区域高分辨率（30 m）和大区域低分辨率（1 km）的植被制图结果。以上两种方法可以为以后不同尺度需求的植被制图研究提供一定的理论基础。 在得到青藏高原多年冻土区植被分布现状的结果后，利用均匀分布于该区域的8个研究区来分析植被生长变化受地理位置和植被类型的影响作用。通过分析1982年到2012年间，8个研究区中不同高寒植被类型（高寒沼泽草甸、高寒草甸、高寒草原和高寒荒漠）中NDVI在植物生长季（每年4月到10月）的变化率可知：在每个研究区中，不同植被类型条件下的NDVI变化速率基本相似；而在不同研究区中，即使是同一种高寒植被类型，其NDVI变化速率也不相同；同时，青藏高原多年冻土区中东部的研究区变化速率明显大于西部区域。因此，青藏高原多年冻土区植被生长变化状况的区域效应远大于植被类型效应。 此外，本文还对该区域碳的源汇效应做出研究。为保证代表植被特征的NDVI数据对当前和未来的植被生长状况有准确的预测，本文首先利用一元线性回归预测模型对NDVI数据做出扩展，使其时间序列覆盖1982年到2014年。这段时间青藏高原植被在生长季的生长存在增长趋势（0.0004 yr-1, r2 = 0.5859, P < 0.001）。因植被生长可以促进碳积累效应，所以青藏高原在这段时间属于碳吸收区。然后，利用扩展后的NDVI数据计算青藏高原多年冻土区的变化率后，通过统计关系计算获得2050年和2070年青藏高原多年冻土区的各种植被特征参数。同时，借助WorldClim数据中心当前、2050年和2070年的生物气候参数以及DEM数据，利用决策树分类方法完成当前、2050年和2070年4种情景（RCP2.6、RCP4.5、RCP6.0和RCP8.5）10种气候系统模式下青藏高原多年冻土区植被类型分布结果。最终结合野外调查获取的地下0-50 cm的土壤有机碳含量可知，该区域当前的碳储量为12.65 Pg。2050年和2070年青藏高原多年冻土区4种情景（RCP2.6、RCP4.5、RCP6.0和RCP8.5）地下0-50 cm的土壤有机碳含量则分别为12.12 Pg、12.25 Pg、12.38 Pg、12.49 Pg、12.23 Pg、12.32 Pg、12.27 Pg和12.80 Pg。因此，青藏高原多年冻土区在增温后，碳的汇效应明显减弱，全球变暖不利于该地区的“固碳”作用。 综上所述，青藏高原多年冻土区在1982年到2014年间，植被属于生长积累时期，在碳循环过程中做出“固碳”的贡献。同时，该区域植被在生长时受地理位置的影响效果远强于植被类型的作用。而随着全球温度上升，该区域在地下0-50 cm处的土壤有机碳含量会减少，很有可能会转变为碳排放区域。 |
| 英文摘要 | Qinghai-Tibet Plateau, a multi-phase combination, has experienced long-term complex geological process. Here has distributed widespread areas with high-altitude region of the world and it is referred to as “the third pole of the world”. A unique natural landscape was located in the plateau, which was leaded this area sensitive to climate change. And the region is an ecological fragile zone also. As the global warming in recent one hundred years, permafrost has degraded seriously in the Qinghai-Tibet Plateau. Previous researches demonstrated that this phenomenon of global warming has still continued in the 21st century. The degradation of permafrost will thicken the thickness of active layer, which have played an important role in the process of vegetation distribution and growth derived from the changes in soil environment by water and heat. As the changes of hydro-thermal condition and vegetation in the permafrost zone of Qinghai-Tibet Plateau, the underlying surface in this region has an opposite effect on the bottom of the atmosphere also. This effect could influence surrounding areas even affect the global climate changes. Meanwhile, the organic carbon content of soil was changed by the magnitude of biomass. Therefore, the distribution and changes of vegetation in the permafrost zone of Qinghai-Tibet Plateau have received great concerns. These researches could provide theoretical support for climate change not only, but also provide key data for the carbon cycle in the permafrost zone of Qinghai-Tibet Plateau, more over for global scale. Based on above reasons, the mean values and changed slope of NDVI are detected by GIMMS NDVI 3g (the third generation products of Global Inventory Monitoring and Studies Normalized Difference Vegetation Index) from 1982 to 2012. In the global map of NDVI, the mean values and changed slope in Qinghai-Tibet Plateau are smaller than them in other regions of the world. Therefore, there is relatively sparse vegetation in this region, and the ecological environment is more fragile in the plateau. Then analysis of the consistency between permafrost distribution and vegetation type which was presented by Jizhou Ren, we find that the environment of permafrost zone in Qinghai-Tibet Plateau should be suitable for alpine meadow grassland, the grassland type was classified by advanced comprehensive and sequential classification of grassland. Then the distribution map of vegetation types for small areas with high spatial resolution (30 m) and large areas with low spatial resolution (1 km) are interpreted by the observation date of vegetation investigation from 2009 September to 2013 September as well as different imagines from remote sensing. The classification method of vegetation map for small areas with high spatial resolution is object-oriented classification with decision tree rules. The study area is Yushu in this classification algorithm, and the overall accuracy and Kappa coefficient for classification are 49.32 % and 0.3735 respectively. When used decision tree only for the vegetation classification method, the overall accuracy and Kappa coefficient for classification are 56.16 % and 0.4394 respectively. Although the accuracy of object-oriented classification with decision tree rules is lower than it of used decision tree only, the result derived from object-oriented classification is more accord with the observation habit from human visual. Because the object-oriented classification is only suitable for extraction features from the images with high spatial resolution, the classification method is used decision tree only for large areas with low spatial resolution, and the average accuracy is 74.5 % from the 10-fold validation in the vegetation distribution for the permafrost zone of Qinghai-Tibet Plateau. These classification methods of vegetation types could be used by various vegetation maps with different scales. By the map of vegetation distribution in the permafrost zone of Qinghai-Tibet Plateau and the GIMMS NDVI datasets of vegetation growth season (from April to October in each year) from 1982 to 2012 for 8 study areas which are distributed in the zone uniformly, the effects of geographical positions and vegetation types to vegetation growth are analyzed. There are alpine swamp meadow, alpine meadow, alpine steppe and alpine desert in the 8 study areas for the permafrost zone of Qinghai-Tibet Plateau. In each study area, the change trends of NDVI for different alpine grassland are different, and the trends of same alpine grassland in different study area are similar. Meanwhile the trends of the eastern in the permafrost zone of Qinghai-Tibet Plateau are larger than them of the western part. Therefore, the effects come from geographical positions are superior to vegetation types to vegetation growth. Moreover the effects of carbon source are detected. And an extended GIMMS NDVI dataset from 1982 to 2014 was presented using a unary linear regression by MODIS dataset from 2000 to 2014 in Qinghai-Tibet Plateau. Compared with previous researches, the accuracy of the extended NDVI dataset was improved again with consideration the residuals derived from scale transformation. With the extended NDVI dataset, we found that in growing season there was a statistically significant increase (0.0004 yr-1, r2 = 0.5859, P < 0.001) in Qinghai-Tibet Plateau from 1982 to 2014. Due to the increased vegetation activity, the magnitude of carbon sink is accumulated in this region during this period. Using the extended NDVI dataset, the vegetation characteristics are calculated in the permafrost zone of Qinghai-Tibet Plateau. According to these characteristics parameters, DEM and bioclimatic variables from WorldClim, the vegetation distribution are predicted by decision tree for present days, 2050 and 2070 using RCP 2.6, RCP4.5, RCP6.0 and RCP8.5 of 10 climate system models. At last, the content of soil organic carbon at present is 12.65 Pg at 0 to 50 cm below the ground surface calculated by the soil organic carbon content of different alpine vegetation types which are acquired from field vegetation investigation. And the contents of RCP2.6, RCP4.5, RCP6.0 and RCP8.5 in 2050 and 2070 are 12.12 Pg, 12.25 Pg, 12.38 Pg, 12.49 Pg, 12.23 Pg, 12.32 Pg, 12.27 Pg and 12.80 Pg respectively predicted by the vegetation distribution. According to these data, the global climate warming will have an opposite effect to carbon accumulate in vegetation of permafrost zone in Qinghai-Tibet Plateau. Therefore, the activity of vegetation in the permafrost zone of Qinghai-Tibet Plateau has increased from 1982 to 2014, and it plays a carbon sink role in global carbon cycle. Meanwhile it can be concluded that the effects come from geographical positions are superior to vegetation types to vegetation growth in this region. In the future, the content of soil organic carbon may be decreased along with the global warming. |
| 中文关键词 | 青藏高原多年冻土区 ; 植被制图 ; 高寒草地 ; 地理位置 ; 植被类型 ; 土壤有机碳 |
| 英文关键词 | Permafrost zone of Qinghai-Tibet Plateau Vegetation map Alpine grassland geographical position vegetation type Soil organic carbon |
| 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/2XILL650/287537 |
| 推荐引用方式 GB/T 7714 | 王志伟. 青藏高原多年冻土区植被生长和分布[D]. 中国科学院大学,2015. |
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