Evaluating Ginkgo Leaf Necrosis and Asymmetric Crown Discoloration Induced by Typhoon 0613 with RGB Image Analysis

Abstract

As one kind of disaster, typhoons can cause serious damage to landscape trees both mechanically and physiologically. The Typhoon 0613 was characterized by strong wind associated with less rainfall when it passed through Yamaguchi City, Japan. After hit by it, the symptoms of leaf necrosis appeared on many ginkgo trees from coast to inland and the crowns of them became asymmetrically discolored. Due to the big body of ginkgo trees, this kind of phenomenon was often described by visual scale method characterized by significant deviation and observer specific. In order to quantitatively estimate the symptoms of damage, the leaf necrotic area percentage (LNAP), crown discoloration area percentage (CDAP) and inflection point (IP) of the threshold response function for asymmetric discolored crowns were determined by image pixel method. The green/luminance (G/L) value was measured by using the RGB images respectively scanned by a flat bed scanner from individual leaves and taken with a CCD digital camera from crowns. Significant relationship between G/Lleaf and LNAP, and between G/Lcrown and CDAP were obtained with the correlation coefficient of R 2 0.941 and R 2 0.826 separately. This suggested that both leaf necrosis and asymmetric crown discoloration of ginkgo trees induced by Typhoon 0613 can be quantitatively estimated by measuring the G/L value from both leaves and crowns. The significant relation between CDAP and IP (R 2 0.811) reveals that both statistically calculated IP value and visually divided CDAP value can be used in estimating the asymmetric crown characters. The estimation of sampled leaves showed that it was the difference of necrotic leaves between windward and leeward made the crown of damaged ginkgo trees appear asymmetrical discoloration. Image threshold responsive analysis of ginkgo crowns hit by Typhoon 0613 indicated that the injury of ginkgo crowns was more serious on windward than leeward. The relationship between the distance from coastline (DC) and G/Lcrown value presented that the farther from the coastline, the bigger the G/Lcrown value of ginkgo crowns. Comparing to the sampling method, image analysis can be more effective being applied in field measurement of damaged status of ginkgo trees hit by severe typhoons for the reason of less labor and less time requirement. It may be an alternative tool to be used in estimating the degree of damage to ginkgo trees by typhoons like Typhoon 0613.

Persistent and advanced reddening of sweetgum leaves after major veins severing

“…It was obtained with image analysis method (Wang et al 2008(Wang et al , 2009a(Wang et al , 2009b to describe the persistent reddening and advanced reddening of leaves. Images were scanned with a scanner (Canon D125u2) or taken with a CCD camera (Canon IXY 6.0).…”

Digital image analysis of different crown shape of Platycladus orientalis

“…In the past, the studies investigating the meteorological impaction on the crown shape of trees were not less (Liu et al, 2009;Solberg, 1999;Ma and Wang, 2006;Zierl, 2004). We have recently engaged in the study of the crown shapes of trees after typhoon events (Wang et al, 2008;Wang et al, 2009a) and the asymmetrical crown of some landscape tree species (Wang and Zhang, 2011). While studying the crown shape of Platycladus orientalis in Shandong Province, China, we observed special tree crowns in torch and fusi-form shapes, reflecting the withering of partial lower twigs, and the normal tower form resulting from the phototropism of lower twigs.…”

“…Among these methods, image analysis is simple, fast and time and money saving (Wang et al, 2009a). Combined with the construction of special meteorological indices, we analyzed the special crown shapes of Platycladus orientalis using the digital image measurement to construct a simple and easily measured index properly responding their health status and site conditions.…”

“…In the present study, the color of canopy RGB images has also been analyzed using the RGB analysis method (Wang and Omasa, 2012) accompanying with G/L value calculation (Wang et al, 2009a).…”