Urban trees are of high importance for healthy urban ecosystems. However, some trees are invasive plants that may ‘escape’ from urban areas into natural environments. Furthermore, invasive forest pests often arrive and establish in urban environments before they spread to forest ecosystems. Therefore, knowledge of tree species composition in urban areas is important for the biosecurity of cities and surrounding forests. Despite this, urban tree inventories often lack information on trees on private properties. To assess the potential role of urban areas as a source of invasive trees as well as invasive pests of trees, we compared the species composition of urban trees in public and private spaces in several Swiss cities and in tree nurseries (henceforth: ‘nurseries’) in Switzerland. We analysed the various data sets we compiled regarding invasive tree species, and examined how many trees are potential hosts for invasive quarantine pests of trees. We found no statistically significant difference in tree species composition in public and private urban areas, but the proportion of non-native trees was higher in private than in public spaces. Tree species available in nurseries and those present in cities were not significantly different, with larger urban tree inventories having a greater overlap with the species available in nurseries. Five of eight tree species considered invasive whose sale was banned since September 2024 were still on sale ten months before the ban came into force. All eight tree species were present in urban tree inventories. Importantly, between 91 % and 97 % of all urban trees in public and private spaces were suitable hosts for at least one quarantine forest pest. Given the pivotal role that urban trees play for the health of urban and peri-urban ecosystems, knowledge of tree species composition is essential from a biosecurity perspective. Our findings suggest that the combination of public urban tree inventories and trees available from nurseries can provide an estimate of the composition of private urban trees and can be useful for invasive species monitoring.

中文翻译：

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公共和私人空间的城市树木以及苗圃提供的树木的生物安全视角


城市树木对于健康的城市生态系统非常重要。然而，有些树木是入侵植物，可能会从城市地区“逃逸”到自然环境中。此外，入侵性森林有害生物通常会在蔓延到森林生态系统之前到达并在城市环境中建立。因此，了解城市地区的树种组成对于城市和周围森林的生物安全非常重要。尽管如此，城市树木清单通常缺乏私人财产树木的信息。为了评估城市地区作为入侵树木和树木入侵害虫来源的潜在作用，我们比较了瑞士几个城市公共和私人空间以及瑞士树木苗圃（以下简称：“苗圃”）的城市树木物种组成。我们分析了我们汇编的有关入侵树种的各种数据集，并检查了有多少树木是树木入侵检疫性害虫的潜在宿主。我们发现公共和私人城市地区的树种组成没有统计学上的显着差异，但私人空间的非本地树木比例高于公共空间。苗圃中的树种与城市中的树种没有显著差异，较大的城市树木库存与苗圃中的树种重叠更大。自 2024 年 9 月以来被禁止销售的 8 种被视为入侵性的树种中，有 5 种在禁令生效前 10 个月仍在销售。所有八种树种都存在于城市树木清单中。重要的是，公共和私人空间的所有城市树木中有 91% 到 97% 是至少一种检疫性森林害虫的合适宿主。 鉴于城市树木对城市和城郊生态系统的健康起着关键作用，从生物安全的角度来看，了解树种的组成至关重要。我们的研究结果表明，公共城市树木清单和苗圃提供的树木相结合可以提供对私人城市树木组成的估计，并可用于入侵物种监测。