複数の手法によるスギの葉面積指数の推定:—熊本県阿蘇地方を事例に—

概要

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We estimated the leaf area index (LAI) of Cryptomeria japonica in Aso district, Kumamoto Prefecture using various methods. In advance, we selected seven sites, which had various values of the normalized difference vegetation index (NDVI), by analyzing satellite imagery (ALOS/AVNIR-2) of September 2006. Around the end of August 2007, we measured the diameters of breast height (DBH) and tree heights at these sites, which were substituted to the universal allometric equation to calculate the dry weight of leaves of Cryptomeria japonica, proposed by Hosoda and Iehara (2010). We then estimated LAI by assuming a typical histogram of green leaf diameters of Cryptomeria japonica. At the sites, we also measured LAI using LAI-2000 and took hemispheric photographs, from which we calculated LAI using LIA32. We also estimated LAI using NDVI calculated from ALOS/AVNIR-2 imagery. Theoretically, indirect estimations of LAI-2000 and hemispheric photographs must be smaller than the allometric LAI; however, at sites with a smaller DBH, indirect estimations were larger than direct ones. This implies the possibility that the allometric equation is not suitable for estimating LAI in densely planted forest stands with a smaller DBH. In addition, we demonstrated that we should measure DBH and tree height of broader trees more accurately to estimate LAI with the equation of Hosoda and Iehara (2010), based on a simple numerical simulation.