秦巴山地植被绿度特征及其对地表水热的响应

地表水热通过影响土壤和大气间的水分交换以及植被生长用水对植被格局起关键作用。使用2000—2020年MODIS叶面积指数(Leaf area index, LAI)作为秦巴山地植被绿度的评价指标，基于遥感技术获取同时段地表温度(Land surface temperature, LST)和温度植被干旱指数(Temperature vegetation drought index, TVDI),用于指示地表水热状况。结合坡向和海拔等地形因素，使用均值和趋势法分析了秦巴山地植被绿度的时空特征；采用时滞相关性分析、主导因素分析探究了植被绿度与地表水热的相关关系，以及影响植被绿度变化的主导因素；借助广义可加模型，结合植被类型探讨了植被绿度与地表水热的非线性关系。结果表明：(1)秦巴山地LAI集中在1—5之间，LAI均值随海拔先增后减，不同坡向LAI差异较大，表现为大巴山北坡>大巴山南坡>秦岭南坡>秦岭北坡>西秦岭。秦巴山地LAI高值区与地表水热较好的地区在空间分布上具有一致性，LAI低值区与LST低值区或TVDI高值区较为一致。(2)秦巴山地LAI以由增变减趋势为主，变...

Vegetation greenness characteristics in Qinling-Daba Mountains and its response to surface hydrothermal

Surface hydrothermal plays a key role in vegetation pattern by affecting soil-atmosphere water exchange and vegetation growth water use. MODIS Leaf area index (LAI) from 2000 to 2020 was used as the evaluation index of vegetation greenness in Qinling-Daba Mountains. Land surface temperature (LST) and temperature vegetation drought index (TVDI) in the same period were obtained based on remote sensing technology to indicate surface hydrothermal conditions. Combined with terrain factors such as aspect and altitude, the temporal and spatial characteristics of vegetation greenness in Qinling-Daba Mountains were analyzed by mean and trend methods. The correlation between vegetation greenness and surface hydrothermal, as well as the leading factors affecting the change of vegetation greenness were explored by time-delay correlation analysis and dominant factor analysis. The nonlinear relationship between vegetation greenness and surface hydrothermal was discussed with the help of the generalized additive model and vegetation types. The results showed that:(1) the LAI of Qinling-Daba Mountains was concentrated in the range of 1-5. The average value of LAI increased first and then decreased with altitude, while the LAI varied greatly in different aspects, which was shown as the north slope of Daba Mountains > the south slope of Daba Mountains > the south slope of Qinling Mountains > the north slope of Qinling Mountains > the west Qinling Mountains. The LAI high value area in the Qinling-Daba Mountains was consistent with the area with good surface hydrothermal in terms of spatial distribution. The LAI low value area was consistent with LST low value area or TVDI high value area. (2) The LAI of the Qinling-Daba Mountains mainly changed from increase to decrease, and the change trend of altitude differentiation was larger than aspect differentiation. In the area of LAI from increase to decrease, surface hydrothermal was mainly from increase to decrease, followed by continuous increase. (3) The LAI of Qinling-Daba mountains was significantly positive correlation with LST, but significantly negative correlation with TVDI. The time lag effect of surface hydrothermal on LAI was not obvious, and LAI was more affected by TVDI than LST. (4) Except for the increase of LST which led to monotonous increase in LAI of deciduous broad-leaved forest and mixed forest, the surface hydrothermal had nonlinear effects on the LAI of various vegetation types. There was a certain threshold, and the response law of LAI on both sides of the threshold was different, and the thresholds of different vegetation''s response to surface hydrothermal were quite different.