Quantitative Research on Vigor of Ginkgo Trees hit by Typhoon 0613 with Ground-based Digital Image Analysis

Abstract

The center of typhoon No.13 (Typhoon 0613) in 2006 passed through the Japan Sea and shaved the southwest corner of Yamaguchi Prefecture with characteristics of strong wind and less rainfall in Yamaguchi City. Many ginkgo (Ginkgo biloba L.) trees showed leaf discoloration and defoliation after its hit in Yamaguchi City, Japan. The crown of them can be clearly divided into green part and non-green part so that they were misrecognised as special ornamental trees. In order to quantitatively study this phenomenon, the indices of green coverage ratio of crown (GCRC), crown coverage (CC), vigor index (VI), and so on were used to analyze the vertical sideward profile of ginkgo trees by ground-based digital image analysis. They reflected leaf discoloration and defoliation of the crowns, and positively related to the distance from coastline (DC). Logistic functions between DC and these indices were obtained, with square correlative coefficients being 0.913, 0.622, and 0.882, respectively for GCRC, CC and VI. There is indication that ground-based digital image analysis can be an effective tool used in evaluating the vigor status of ginkgo trees hit by Typhoon 0613. In the paper, combined with analysis of meteorological data, the reason for damage to ginkgo trees was considered as water stress induced by Typhoon 0613. Based on multi-analysis of the research, there were significant differences of vigor status between coast and inland ginkgo trees after hit by Typhoon 0613.