Journal of the Japanese Society of Revegetation Technology

Black locust (Robinia pseudoacacia L.) is an invasive alien plant which has caused considerable changes in the ecosystems of Japanese riparian and coastal forests. In this study, we examined the allelopathic activity of heartseed walnut (Juglans ailanthifolia Carr.), a species native to China, Korea and Japan. The rhizosphere soil of heartseed walnut inhibited the growth of black locust, and it was suggested the possibility that this inhibition was caused by juglone (5-hydroxy-1,4-naphthoquinone) released from the root of heartseed walnut. Heartseed walnut inhibited the growth of seedlings of black locust about 50% in mixed cultivation for 45 days. In this cultivation, concentration of the juglone in the soil was 1.2%×10^-6g g^-1. As EC₅₀ (concentration to suppress the growth to 50%) for black locust by purified juglone is 3×10^-6g g^-1, it was evaluated that this concentration is high enough to explain the inhibitory activity of heartseed walnut to blacklocust in mixed culture.

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In order to evaluate solar shading effects in the thermal environment of parking lots, the temperature of ground surface, and the inside and outside of car bodies were measured on sunny and shaded sides. In summer daytime, the maximum difference between the ground surface temperature of sunny and shaded sides was 22.2°C, while it remained 2°C-5°C on the lawn and shaded side. Car body temperatures showed 12°C-30°C difference between sunny and shaded sides. The car body temperatures were similar to the air temperatures on theshadedsideat the lowest temperatures. The drops of ground surface/car body temperatures were strongly affected by the cover ratio of the sun shade net, but it hit a ceiling at 80%. Drops of temperature were not affected by the temperature of the sun shelf material. In summer daytime, leaf surface temperature was maintained lower than air temperature due to transpiration. The material originates plant decrease radiation more than other solar shading materials.

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On a cut slope in Mohka city, Tochigi, the regeneration of the alien species, Amorpha fruticosa L., after extermination management by mowing and applying herbicide, was investigated. The management was conducted in July, 2007. The number of individuals and sprouts and diameter of the main stems of A. fruticosa were investigated in October, 2007 or the current year, and two years later in August, 2009. In 2009, the height of individuals and the number of infructescences and seeds were also investigated. In 2009, A. fruticosa regenerated the shrub community to height of about 2 m, and the number of individuals in 2009 was higher than that in 2007. Many sprouts of A. fruticosa appeared in 2007, and the number of sprouts in 2009 was less than in 2007. The diameter of main stems increased in 2009 as well as in 2007, and the half of individuals produced fruits. The extermination management by mowing provided an opportunity for the community of A. fruticosa to reproduce and also to regenerate by sprouting.

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