青藏高原草地非光合植被覆盖度时空动态

Spatio-temporal variations in non-photosynthetic vegetation cover on the Qinghai-Tibet Plateau grassland

估算非光合植被覆盖度(f_(NPV))对于自然资源的合理利用、生态系统碳平衡以及气候变化等具有重要意义。青藏高原具有独特的气候特征和丰富的植被类型,在全球生态系统中发挥着至关重要的作用。本研究以青藏高原草地为研究区,以MODIS 500 m分辨率地表反射率产品MOD09A1为数据源,利用归一化差异耕作指数(NDTI)构建非光合植被像元二分模型估算了青藏高原草地f_(NPV),并利用趋势分析法和相关分析法研究青藏高原草地f_(NPV)的动态变化及其与气候因子的关系。结果表明:非光合植被像元二分模型可以有效估算青藏高原草地f_(NPV);青藏高原草地f_(NPV)呈现从西北至东南逐渐升高的分布情况,这与青藏高原的地形和气候因素密切相关;2000-2020年青藏高原草地f_(NPV)以每年0.0012%的速度增加,且整体变化趋势不明显;青藏高原草地f_(NPV)与降水呈正相关关系,在西南部分地区呈负相关关系;在研究区中部和东部地区f_(NPV)与温度呈正相关关系,东南、南部和西南地区与温度呈负相关关系;研究区内f_(NPV)与温度的相关受到降水的微弱影响,f_(NPV)与降水的相关性几乎不受气温的影响,且f_(NPV)受5月-9月均温和1月-12月累积降水量的影响较大。本研究提供了一种新方法对非光合植被覆盖度进行估算,研究结果为青藏高原非光合植被覆盖度的研究提供依据。

Estimating the fractional cover of non-photosynthetic vegetation(f) is of great importance for managing grassland resources, calculating carbon balance, and adapting to climate change. The Qinghai-Tibet Plateau has unique climatic characteristics and rich vegetation types that play an important role in the global ecosystem. In this study, we first developed a method for estimating fusing a dimidiate pixel model and normalized difference tillage index(NDTI)without field measurements. The model assumes that a mixed pixel is a linear combination of non-photosynthetic vegetation and bare soil, and their coefficients represent the proportion of the area occupied by non-photosynthetic vegetation and bare soil in that pixel. The model was then used to estimate the grassland fon the Qinghai-Tibet Plateau from the year 2000 to 2020 using MODIS surface reflectance data at 500 m resolution(MOD09A1). Statistical analyses were used to further examine the spatio-temporal variations in grassland fon the Qinghai-Tibet Plateau and their relationship with climatic factors. The results showed that the proposed dimidiate pixel model was capable of estimating fof the Qinghai-Tibet Plateau grasslands. The grassland fon the Qinghai-Tibet Plateau gradually increased from northwest to southeast. This trend was closely related to the topography and climatic factors of the Qinghai-Tibet Plateau. The grassland fon the Qinghai-Tibet Plateau was positively correlated with precipitation, and negatively correlated with precipitation in parts of the southwest. Temperature and fwere positively correlated in the central and eastern parts of the study area, whereas in the south, southeast, and southwest, fwas negatively correlated with temperature. The correlation between fand temperature in the study area was not significantly affected by precipitation, the correlation between fand precipitation was almost unaffected by temperature, and fwas significantly affected by the mean precipitation received between May and September and the accumulated precipitation received between January and December. Our study provides a new approach for estimating the fand a new idea for the dynamic monitoring of non-photosynthetic vegetation on the Qinghai-Tibet Plateau.