SPECIAL ISSUE “Nonnative Species and Vegetation Management” Present status on Ailanthus altissima (Mill.) Swingle escaped from national road route 9, which planted as street tree and evaluation of its invasiveness

Abstract

Heaven tree (Ailanthus altissima (Mill.) Swingle) is deciduous, broad leaved, dioecious, samariform tree originated in northern and midland of China. This species was introduced into Japan in 1875 as street/garden tree, and it escaped into non-build up area and river bed. There are many reports that this species invaded into non-native area and negative effects for ecosystem. However, there are few studies on this species in Japan, especially, from estimating invasiveness point of view. The authors aim to clarify present status of this species escaped from National Road 9 in Tottori city and estimate its invasiveness. A study area was set on and around National Road 9 in western suburb of Tottori city, the area size is approximately 202 ha. Location, tree height, stem circle length at breast height, sprout and standing environment was recorded for each individuals. Invasiveness of the species was estimated based on both field work in Tottori and two models. The model by Pheloung suggests risk of introduction in advance while the John and Linda model judges invasiveness after introduction. As a result, 1) Local population of Heaven tree in the study area expanded their distributed area especially upon the leeward of the mother trees originated street trees. 2) Escaped individuals which cut the part above ground level can re-grow and be source of distribution by dispersion of seeds and root sucker. 3) Estimation of invasiveness by two models suggested that Heaven tree has strong invasiveness.