Estimation of Mangrove Leaf Area Index from ALOS AVNIR-2 data (A Comparison of Tropical and Sub-Tropical Mangroves)

摘要

Measuring and monitoring mangrove Leaf Area Index (LAI) is an essential part of monitoring and management of mangrove environments. This study investigated the use of ALOS AVNIR-2 (AVNIR-2) image data for LAI estimation in mangrove environment through semi-empirical analysis, and compared and contrasted the results with different mangrove environmental settings and vegetation structures at sites in tropical Karimunjawa Island (KI, Indonesia) and sub-tropical Moreton Bay (MB, Australia). We used Normalized Difference Vegetation Index (NDVI) as a proxy to estimate LAI in both sites. The results indicated that the regression analyses showed significant coefficient of determination (R~2) values of 0.82 at KI and 0.83 at MB. The range of LAI values for KI from 0.88 to 5.33 (n = 76, mean = 2.98, SD = 1.04) and for MB from 0.26 to 3.23 (n = 120, mean = 1.97, SD = 0.45). In terms of site comparison, we found that the results of LAI estimation from field measurement and remote sensing data varies across sites; the Karimunjawa Island mangroves had a comparatively wider range and variation of LAI values than the Moreton Bay mangroves. This difference was attributed to the difference in stand heterogeneity and species composition. Further investigation shows that mangrove LAI values are independent of the mangrove structural formation (i.e. scrub, low-closed forest, closed forest, etc.). Instead, the LAI value depends on the local spatial variation of mangrove phenological stages and canopy cover. The findings provide an understanding of the spatial variation of mangrove vegetation structure for estimating LAI.