Invasive alien plants have caused negative ecological and economic impacts and numerous studies have focused on determining which traits make these plants successful invaders. Although it is commonly believed that only a small proportion of introduced species can become invasive, it is unknown why many alien species fail to establish. In order to identify the alien species that are exhibiting a limited distribution in their new habitat, the vegetation in an international trading port, which is a primary site for the introduction of alien plants, and residential areas of Kobe, western Japan, were surveyed every month from April–October, 2014. A total of 167 species, of which 59.3% were annual and 61.2% were alien, was found. Species that originated in Mediterranean regions were the dominant alien species, followed by those from North America. A principal component analysis showed that the species compositions were different between the port and the residential areas, particularly in spring. The species from the port areas were major weeds from the cereal crop fields of North America and Australia, but were limited in distribution in Japan. The residence time might be too short to allow them to expand or climatic differences between the areas where these aliens are naturally dominant and Japan could serve as ecological barriers to the range expansion of such species.

中文翻译：

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日本神户国际贸易港和居民区的植物物种组成

外来入侵植物对生态和经济造成了负面影响，许多研究集中在确定哪些特性使这些植物成功入侵。尽管通常认为只有一小部分的引进物种会成为入侵物种，但未知为什么许多外来物种无法建立。为了确定在新栖息地中分布有限的外来物种，对国际贸易港口（引进外来植物的主要地点）的植被和日本西部神户的居住区进行了调查， 2014年4月至10月的一个月。共发现167种，其中一年生59.3％，外来物种61.2％。起源于地中海地区的物种是主要的外来物种，其次是来自北美的物种。主成分分析表明，港口和居民区之间的物种组成有所不同，尤其是在春季。来自港口地区的物种是北美和澳大利亚谷物作物田的主要杂草，但在日本的分布有限。停留时间可能太短，无法让他们扩大，或者这些外来人自然占主导的地区之间存在气候差异，日本可能成为此类物种范围扩大的生态障碍。