Abstract Urban natural green spaces are becoming increasingly impacted by anthropogenic disturbances, promoting alien plant invasions. Using a rapidly developing city in South Africa as a case study, we related distribution, composition, and ordering of alien plant species to environmental and anthropogenic factors to identify drivers of invasiveness. Vegetation surveys were used to identify and quantify (in terms of composition and density) alien species within 30 natural green spaces. Floristic characteristics were then related to levels of non-natural disturbance and selected abiotic parameters. Based on the relationships observed, selected floristic parameters were used to develop an Alien Invasive Index to identify ‘invasive alien hotspots’. Collectively, 80 alien plant species (from 30 families) were found, 35 of which are invasive. The most speciose families were Asteraceae > Fabaceae > Verbenaceae. Their representatives, specifically the invasive shrubs Lantana camara (Verbenaceae) and Chromolaena odorata (Asteraceae) and alien herbs Conyza sumatrensis, Bidens pilosa and Tagetes minuata (Asteraceae) were also the most dominant in terms of frequency across sites and density. A Principal Component Analysis showed invasive alien plant species composition to be most strongly related to level of disturbance, followed by distance to informal settlement and soil moisture content. The Alien Invasive Index could discriminate between sites with low and high levels of invasiveness, and its suitability was validated by the fact that sites with very high index values were in close proximity to informal settlements. The study demonstrates the value of combining classical in situ vegetation surveys and overlay analysis using Geographic Information System for prioritising green spaces and alien species for management in cities that are limited in terms of financial resources.

中文翻译：

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城市中的外星人：在城市矩阵中确定非本土植物区系热点

摘要 城市自然绿地越来越受到人为干扰的影响，促进了外来植物的入侵。我们以南非一个快速发展的城市为例，将外来植物物种的分布、组成和排序与环境和人为因素联系起来，以确定入侵的驱动因素。植被调查被用来识别和量化（在组成和密度方面）30 个自然绿地内的外来物种。然后，植物区系特征与非自然干扰水平和选定的非生物参数相关。根据观察到的关系，使用选定的植物区系参数来制定外来入侵指数，以识别“外来入侵热点”。总共发现了 80 种外来植物物种（来自 30 科），其中 35 种是入侵植物。最特殊的科是菊科>豆科>马鞭草科。它们的代表，特别是侵入性灌木马缨丹（马鞭草科）和菊苣（菊科）以及外来草本植物 Conyza sumatrensis、Bidens pilosa 和万寿菊（Tagetes minuata）在跨地点频率和密度方面也是最主要的。主成分分析表明，外来入侵植物物种组成与干扰程度的相关性最强，其次是与非正规定居点的距离和土壤水分含量。外来入侵指数可以区分具有低侵入性和高侵入性的地点，其适用性通过具有非常高指数值的地点靠近非正规住区这一事实得到验证。