漓江上游流域森林景观格局对土壤水分空间异质性的影响

As a typical tourism region of China and one of the hotspot of terrestrial biodiversity with international significances, the Li River plays an important role in the local sustainable development and ecological stability of Guilin. However, with the fast growth of the population, the rapid developing of industry and agriculture, the deterioration of forest ecosystem and unreasonable plantation, the phenomenon of seasonal drought of the Li River is getting more seriously. Therefore, this study will try to find out the causes that attributed to the seasonal drought of the Li River with the overlay analysis of forest landscape changes and spatial heterogeneous of soil moisture. At first, three forest landscape changed modes namely infilling, edge-expansion and leapfrog, and their characteristics will be analyzed with different periods of remote sensing data and LEI (landscape expansion index) method. The remote sensing data will be calibrated with field investigation, land use types and regional administrative map firstly. Then the forest landscape will be classified with the Clump and Majority/Minority Analysis according to the calibrated remote sensing data. And the three different forest landscape changed modes and their characteristics will be analyzed with the GIS and LEI method. Secondly, the surface soil moisture, soil temperature and soil types will be measured and investigated in different forest landscape types according to the forest landscape classification map. Based on these previous works, the coefficients of TVDI (Temperature-Vegetation Dryness Index) formula will be calibrated with the NDVI and temperature data extracted from TM/MSS, CBERS (China-Brazil Earth Resource Satellite) and MODIS remote sensing images. The different periods of spatial heterogeneous of soil moisture and their responses to forest landscape changes will be analyzed with calibrated TVDI formula and geo-statistics method. Last but not least, the causes of seasonal drought of the Li River will be discussed with the overlay analysis of forest landscape changes and spatial heterogeneous of soil moisture from the 1970s. With these works, it is expected to understand the effects of forest landscape changes and spatial heterogeneous of soil moisture on seasonal drought of the Li River, and to provide the practical and scientific knowledge for vegetation rehabilitation, water resources sustainable management and ecological restoration of the Li River and other similar typical tourism regions.

漓江是喀斯特脆弱生态环境下的典型旅游区和具有国际意义的陆地生物多样性关键地区和热点地区之一。然而，随着城镇化、工农业发展速度加快，漓江上游流域森林结构发生巨大变化，水源林遭受严重破坏，水源涵养功能下降，流域水资源生态问题日益严峻，严重影响区域生态稳定和可持续发展。针对漓江流域日益突出的季节性干旱问题，本项目拟以漓江上游流域为研究区域，通过遥感和野外GPS定点调查相结合的方法，从大尺度的角度分析近40年来流域森林景观斑块格局变化模式及其特征；采用温度-植被指数法和地统计学方法对土壤水分进行遥感反演，分析不同时期流域土壤水分空间异质性及其对森林景观斑块格局变化的响应；最后，利用不同时期森林景观斑块格局和土壤水分空间分布格局相叠加分析的方法探讨流域日益严重的季节性干旱问题，以期为典型旅游区退化生态系统植被修复、水资源管理和生态重建提供重要的科学依据。

随着社会经济发展速度加快，作为喀斯特脆弱生态环境下的典型旅游区和具有国际意义的陆地生物多样性关键地区和热点地区之一——漓江流域森林结构发生巨大变化，水源林遭受严重破坏，水源涵养功能下降，流域水资源生态问题日益严峻，严重影响区域生态稳定和可持续发展。本项目以漓江上游流域为研究区域，利用LEI（Landscape Expansion Index）指数分析近40年来流域森林景观变化模式及其特征；采用温度-植被干旱指数（TVDI，Temperature Vegetation Dryness Index）和地统计学方法对表层土壤水分进行遥感反演，分析土壤水分空间分布及其对森林景观变化的响应；最后，基于流域表层土壤最小持水量和多年日平均降雨量探讨流域干旱问题。结果表明：（1）1977～2015年，漓江上游流域所占比例最大为林地，约为70.90%～74.98%。其林地森林景观变化模式以斑块边缘模式为主，即在原有的森林景观边缘向外扩展；其中，以2000至2015年期间变化最为明显。森林景观变化斑块主要分布在城乡工矿居民用地附近，受人为影响较大。（2）2015年TVDI指数等级相比1987和2001年较小，流域表层土壤水分相对较高。表层土壤水分分布具有一致性，即在流域上游猫儿山源头TVDI指数较低，表层土壤水分较大；而在出水口附近为城乡工矿居民用地比较集中，TVDI指数较高，表层土壤水分较小。（3）NDVI在一定程度上影响流域的TVDI分布，NDVI越高，TVDI越低，其所在区域的表层土壤水分越高，其中以流域上游的猫儿山国家自然保护区最为明显；而以城乡工矿居民用地为主的兴安、灵川和桂林市城区的NDVI主要以裸地为主，其TVDI等级较高，表层土壤水分较低。（4）因降雨与表层土壤所需最高土壤含水量的分布不一致性，NDVI分布最大的流域上游源头地区，在降雨量不足的情况下，加上植被的蒸腾耗散，土壤含水量相比其它地区降低，为较易引起干旱发生地区。本研究结合遥感影像并基于LEI和TVDI等指数可以分析不同时期流域森林景观变化格局和反演土壤水分的空间分布特征，在一定程度上可为流域资源管理、土地利用优化模式以及水资源可持续利用提供理论依据。