Estimation of ginkgo leaf necrosis induced by Typhoon 0613 with spectral reflectance

Abstract

Typhoon No.13 in 2006 (Typhoon 0613) passed through Yamaguchi Prefecture, Japan on Sep.17, 2006. After being hit by it, many landscape trees, especially ginkgo in Yamaguchi City, showed symptoms of necrosis on the leaf tip and margin, and even the entire leaf. It clearly divided the crowns of some ginkgo trees into the green part and the non-green part. In order to quantitatively study this phenomenon, the normalized difference vegetation index (NDVI) near red edge for ginkgo leaves, measured by a pocket radiometer in the lab, was used to estimate leaf necrosis induced by Typhoon 0613. Based on this research, the optimum wavelength for calculation of the NDVI value of ginkgo leaves damaged by Typhoon 0613 is 679 and 755 nm, which sufficiently corresponds to variance in ginkgo leaf necrosis. By leaf necrosis investigation, the difference in the percentage of necrotic leaves between the windward and leeward sides made the crowns of damaged ginkgo trees show different colors on either side of the crown. An inverse linear relationship between the necrotic area percentage (NAP) and NDVI755nm/679nm was obtained for ginkgo leaves. By analysis of the NDVI using ratio (NDVIr) value of crowns, it was indicated that there were differences in leaf necrosis induced by Typhoon 0613 among sites of different distances away from the coastline and between ginkgo and other tree species. It has potential to be an alternative tool for evaluating the damage status of ginkgo trees hit by typhoons like Typhoon 0613.