藏西南高原植被NDVI时空变化及其与海拔梯度的关系

青藏高原植被分布不仅与区域水热条件密切相关,而且受海拔和地形的共同影响,认知植被与海拔梯度的关系对青藏高原生态保护具有重要科学和现实意义。基于MODIS NDVI数据和植被类型数据,分析了藏西南高原近21年来不同植被类型生长季NDVI时空变化特征,探讨了植被覆盖与海拔梯度的关系。结果表明:藏西南高原植被类型有森林、荒漠、草原、草甸、高山植被、栽培植被、灌丛和其他植被8种; 随时间推移,各植被类型NDVI均显著增加且在2017年达到最大值。研究区草原、草甸、灌丛和高山植被的增加速率依次为0.006/10 a,0.004/10 a,0.01/10 a和0.006/10 a。除了局地植被呈退化趋势外,绝大部分植被覆盖不断改善。草原、草甸、灌丛和高山植被主要集中分布在海拔4 000 m以上的地区,NDVI在各海拔梯度上均存在较大差异。不同植被类型NDVI随海拔升高均呈现不同的减小趋势,不同年份间同种植被NDVI随海拔梯度变化具有相似的变化趋势。研究结果可为藏西南高原生态建设、植被恢复和畜牧业发展提供一定的科学依据和决策支持。

Spatiotemporal Variation of Vegetation NDVI and Its Relationship with Altitude Gradient in Southwest Tibet Plateau

Vegetation distribution in the Qinghai-Tibet Plateau is not only closely influenced by regional hydrothermal conditions, but also affected by the altitude and topography of the plateau. Understanding of the relationship between vegetation and altitude gradient is of great scientific and practical significance to the ecological protection of the Qinghai-Tibet Plateau. Based on MODIS NDVI data and vegetation type data, we analyzed the spatial and temporal variation characteristics of NDVI during the growing season of different vegetation types in the Southwest Tibetan Plateau in the past 21 years, then explored the correlation between vegetation cover and elevation gradient based on DEM data. The results show that there are eight vegetation cover types in the Southwest Tibet Plateau. including forest, desert, grassland, meadow, alpine vegetation, cultivated vegetation, shrub, and other vegetation types; the NDVI of each vegetation type kept increasing and reached their maximum value in 2017; the increasing rates of grassland, meadow, shrub and alpine vegetation in the study area were 0.006/decade, 0.004/decade, 0.01/decade and 0.006/decade, respectively; in addition to the local vegetation degradation trend, most of the vegetation coverage continued to improve; grassland, meadow, shrub and alpine vegetation mainly concentrate in the area with an altitude of more than 4 000 m, and NDVI has great differences in each elevation gradient; the NDVI of different vegetation types showed different decreasing trends with the increase of altitude, and the NDVI of the same vegetation had similar changing trends with the change of altitude gradient in different years. These results can provide the scientific support for decision-making for ecological construction, vegetation restoration, and animal husbandry in Southwest Tibet Plateau.