Distribution of two naturalized trees, Ailanthus altissima and Toona sinensis, in a rural area of the northern Kami-ina district, central Japan

Tree of heaven (Ailanthus altissima) and Chinese toon (Toona sinensis) trees were introduced to Japan before the 20th century. Although the seeds of both species are dispersed by wind, only the former has become an invasive exotic species in Japan. By comparing the distribution patterns and seed properties of these two species, useful information for preventing the expansion of invasive exotic plants could potentially be obtained. In this study, survey sites were established along four arterial roads running almost parallel to each other in a rural area of the northern Kami-ina district, Nagano Prefecture, central Japan; the locations and number of individuals in each habitat were recorded for both species on either side of the roads over a distance of about 12 km. The environments along the roads were classified into seven vegetation categories. The weight and size of samaras (i.e., winged achenes) from both species in the survey area were measured in surveys that were conducted from the summer to the fall of 2020. The results showed that Ailanthus altissima and Toona sinensis were distributed in 20 and 7 habitats, respectively. Ailanthus altissima was found in all of the vegetation categories, whereas Toona sinensis was unevenly distributed among three vegetation categories. The weight and wing area of Ailanthus altissima samaras were significantly larger than those of Toona sinensis. The deviation in the weight of Toona sinensis samaras was large and produced a bimodal histogram, suggesting that a large number of immature samaras were produced. Consequently, the ability to colonize a greater variety of habitats coupled with the ability to produce fewer immature samaras could potentially increase range expansion by Ailanthus altissima.Article環境科学年報 43 : 66-72, (2021)journal articl