1. Temperate deciduous forests in the United States are located in the most densely populated states across the northern and mid-Atlantic east coast. Land development and associated human activities result in small forests that are susceptible to anthropogenic influences, such as urbanization and non-native plant invasion.
2. The overall objective of this study was to assess spatial and temporal drivers of forest vegetation structure and diversity in small forests embedded across developed landscapes. We assessed woody plant composition across spatial gradients (i.e., urbanization and non-native plant invasion) and a temporal gradient (i.e., time since canopy closure) across 38 forests along the east coast of the United States in northern Delaware and southeastern Pennsylvania.
3. Surprisingly, we found the invasion gradient was not related to the urban gradient across our forests. Across all forests, the canopy consisted of native species (98% of all trees), whereas the forest understory was most vulnerable to non-native plant invasion (65% of all woody plant stems). Greater native species richness in forest canopies and understories with increasing urbanization supports the conclusion that urban forests maintain native species and are not inherently degraded ecosystems. Non-native plant invasion has a strong influence on understory plant communities, and the duration of intact forest canopy had a strong negative correlation with non-native plant invasion suggesting intact forests can resist invasion.
4. Synthesis. This is the first study to compare simultaneously the importance of invasion and urbanization in determining plant community composition in forests embedded across developed landscapes, and to discover that younger forests harbor more invasive plants and urban forests maintain native plants.

中文翻译：

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遍布发达景观的温带落叶林：较年轻的森林藏有入侵植物，城市森林则养有原生植物

1. 美国的温带落叶林位于北部和中大西洋东海岸人口最稠密的州。土地开发和相关的人类活动导致小型森林容易受到人为因素的影响，例如城市化和非本地植物的入侵。
2. 这项研究的总体目标是评估遍布发达景观的小森林中森林植被结构和多样性的时空驱动力。我们评估了北特拉华州和宾夕法尼亚州东南部沿美国东海岸的38种森林中的空间梯度（即城市化和非本地植物入侵）和时间梯度（即从树冠关闭以来的时间）的木本植物组成。
3. 令人惊讶的是，我们发现入侵梯度与整个森林的城市梯度无关。在所有森林中，冠层均由本地物种组成（占所有树木的98％），而林下层最容易受到非本地植物的入侵（占所有木本植物茎的65％）。随着城市化程度的提高，林冠层和林下层中的丰富的本地物种更加丰富，这支持了以下结论：城市森林保留着本地物种，而不是固有的退化的生态系统。非本地植物入侵对林下植物群落有很大影响，完整林冠层的持续时间与非本地植物入侵有很强的负相关性，表明完整森林可以抵抗入侵。
4. 综合。这是第一项同时比较入侵和城市化在确定遍布发达景观的森林中的植物群落组成方面的重要性的研究，并发现年轻的森林拥有更多的入侵植物，而城市森林则保留原生植物。