2000－2018年广西植被时空变化及其对地形、气候和土地利用的响应

广西是典型的喀斯特地区，其生态系统非常脆弱。为评估广西植被时空变化特征及其影响因素，该研究基于2000－2018年MODIS数据，利用最大值合成和趋势分析等方法，分析广西植被NDVI时空变化特征；基于相关分析等方法，结合地形因子、气候因子和土地利用数据，探讨了植被NDVI对地形、气候变化和土地利用的响应。结果表明：1）2000－2018年广西植被NDVI呈增加趋势，但空间差异显著，表现为北高南低，边缘高中间低。2）随着高程的增加植被NDVI呈现先增加再减少的趋势；随着坡度的增加植被NDVI呈先增加至稳定再减小的趋势；除无坡向以外，坡向的不同对植被NDVI影响不大。3）广西2000－2018年气温和降水对植被NDVI为正影响，复相关系数达到0.32。在不同土地利用类型上，植被NDVI对气候的响应是不同的。研究结果揭示了广西植被时空变化特征及其对地形、气候和土地利用的响应，能够为广西可持续发展和生态环境建设提供决策支持。

Temporal and spatial variation of vegetation and its response to topography, climate and land use in Guangxi during 2000-2018

A typical karst landform is widely distributed in Guangxi Province of southern China. Therefore, it is very necessary to explore the temporal and spatial variation characteristics of vegetation in this area. Particularly, the influencing factors can greatly contribute to further promote the green development and ecological environment protection in recent years. Among them, the normalized difference vegetation index (NDVI) can serve as an important indicator to evaluate the crop growth, farmland, land management, and crop production. It is highly urgent to monitor and then predict the changes of vegetation cover in this region. This article aims to investigate the characteristics of temporal and spatial variation in the vegetation NDVI in Guangxi Province of China using the MODIS NDVI time series data from 2000 to 2018. The maximum value synthesis and trend analysis were also utilized to combine DEM data, land use types, temperature, and precipitation data, thereby to explore the NDVI spatiotemporal changes of different vegetation types, as well as the response to climate factors under various terrain conditions and land use. The results showed that: (1) NDVI presented an increasing trend from 2000 to 2018 in the study area, with a linear growth rate of 0.004/a, and an average NDVI value of 0.81. The largest NDVI value was also found in the third quarter. Moreover, the spatial distribution of vegetation NDVI was distributed in the north and edge, but less in the south and middle. The specific areas with high vegetation coverage were mainly concentrated in Hechi, Baise, and Guilin City. There was an overall increasing trend of vegetation NDVI from 2000 to 2018, particularly distributed in southern Qinzhou and Nanning City, accounting for 43.9% of the total study area. (2) The vegetation NDVI first increased and then decreased, and finally stabilized above 0.8, as the elevation increased in the study area. Specifically, the distribution of elevation was higher in the northwest and lower in the southeast, in total between 0-1000m. Furthermore, the vegetation NDVI first increased to stable and then decreased, as the slope increased, where the slope was mainly distributed in between 0-34°. Correspondingly, there was little effect of slop difference on the vegetation NDVI, except for the plain. (3) The annual average temperature was between 18°C and 21°C in the study area from 2000 to 2018, while the average precipitation was between 1100mm and 1900mm. Temperature and precipitation posed a positive effect on the vegetation NDVI, where the multiple correlation coefficient reached 0.32. The response of vegetation NDVI to climate varied significantly in the different types of land use. Specifically, the vegetation NDVI greatly responded to air temperature, but less to precipitation in residential and unused land. By contrast, the response of vegetation NDVI to precipitation was greater than that to temperature in cultivated land, woodland, grassland, and water area. Consequently, there was a relatively significant growth trend of vegetation NDVI in Guangxi Province from 2000 to 2018, indicating that an excellent progress in the continuous implementation of afforestation, the conversion of farmland to forests, and ecological protection projects to curb rocky desertification.