2000-2014年黄土高原植被叶面积指数时空变化特征

研究植被叶面积指数(LAI)时空变化特征,对植被的水土保持效具有重要意义.利用MOD15A2H遥感产品,基于Mann-Kendall趋势检验与Sen斜率分析方法,提取区域尺度与像素尺度上的植被LAI变化特征,并基于不同子流域、坡度、坡向及植被覆盖类型,对植被LAI的变化特征进行分析.基于MOD44B遥感产品,利用线性回归和偏相关系数,分析植被LAI的变化原因.结果表明:1)黄土高原2000-2014年,植被LAI呈显著增加趋势,其年绝对变化幅度为0.042,年相对变化程度为2.71％.2)空间上,在黄土高原58.6％的区域,LAI呈现显著增加趋势,仅有0.9％的区域LAI呈现显著减少趋势.植被LAI剧烈增加,主要发生在河口—龙门区间,包括皇甫川、窟野河、无定河和延河.植被在15°～35°的坡度上,LAI变化程度最剧烈,其变化在各坡向上没有显著差异,农田和草地的LAI变化程度最剧烈.3)与植被总覆盖度相比,植被垂直维结构与黄土高原植被LAI的变化更为相关,其中树木覆盖度的增加,是植被垂直维结构变化的重要原因之一.

Spatio-temporal change analysis of leaf area index in the Loess Plateau during 2000-2014

Background] Vegetation structural characteristic is an important factor determining soil and water conservation effect of vegetation,and leaf area index (LAI) is one of the most important vegetation structural characteristics.Remote sensing technology is the most effective tool to monitor LAI dynamics at regional scale.Methods] In this paper,the spatio-temporal variation characteristics of LAI,including changed area percentage,absolute change rate and relative change rate,at regional scale and pixel scale were investigated respectively using Mann-Kendall trend analysis and Sen-slope analysis based on MOD15A2H product.And variation characteristics of LAI for different sub-basins,slopes,aspects and vegetation types were analyzed and compared.In addition,the reason of variation of LAI was explored using linear regression method and partial relation analysis based on MOD44B product.Results] 1) The change trend of LAI during 2000-2014 in the Loess Plateau increased significantly,and the absolute change rate and relative change rate of LAI were 0.042/Year and 2.71％/Year respectively.2) For the spatial distribution of variation characteristics of LAI,areas with a significant increase trend of LAI accounted for 58.6％ in the Loess Plateau,and areas with a significant decrease trend of LAI accounted for 0.9％ in the Loess Plateau.The variation extent of LAI in the regions between Hekou and Longmen,including Huangfuchuan,Kuyehe,Wudinghe and Yanhe were tremendous.The change rate and area percentage of changed regions for LAI in the area where slope was between 15° and 25° were the highest.There was no significant difference for LAI in different aspects.The change rate and area percentage of changed regions for LAI in cropland and grassland were the highest.3) In the Loess Plateau,the increase of tree coverage was the main reason for increase of vegetation LAI,and there were no significant relationship between LAI and vegetation fractional coverage.Conclusions] The change trend of LAI during 2000-2014 in the Loess Plateau is significantly positive.Compared with absolute change rate,relative change rate is more able to illustrate the variation extent of LAI.According to statistical analysis,compared with total vegetation fractional coverage,LAI is more related to the vegetation vertical structure in the Loess Plateau,and the increase of tree coverage caused by "Grain to Green" project carried out across the Loess Plateau could be one of the important reasons for improvement of vegetation vertical structure.