Not all urban greenspace is the same. Natural area forests can provision more benefits than designed landscapes, and healthy natural area forests can provide more benefits than degraded and invaded forests. Yet there is little information about the scale of natural areas in cities and their management systems. We used data sets on city parkland from across the United States and surveyed practitioners to understand urban natural area forest extent and management. We find that urban natural areas are a dominant greenspace landcover, accounting for 68% of total city parkland across 96 of the most populous cities in the United States in 2019. In the same cities over a five-year period (2014–2019), natural area parkland decreased by 4% (15,264 hectares). At municipal scales, most cities are managing forested natural areas to conserve native species. Across the 108 organizations and 92 cities that responded to our online survey, many different management interventions are being used to steer forest structure and composition. These activities and their outcomes are being tracked nearly 70% of the time by the managing organizations, suggesting a strong data basis for adaptive management. However, challenges exist: 94% of organizations cite invasive species and limited funding as primary challenges. Lack of data and low public awareness of the value of natural areas are also considered primary challenges by more than 70% of the organizations surveyed. As cities embark on efforts to expand and improve greenspace, protecting natural area parkland from development and addressing the challenges managers of these ecosystems face are two very important goals.

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美国城市的自然区森林：机遇与挑战

并非所有的城市绿地都是一样的。天然林可以提供比设计景观更多的收益，健康的天然林可以提供比退化和入侵森林更多的收益。然而，关于城市自然面积及其管理系统的信息很少。我们使用了来自美国各地的城市林地的数据集，并对从业人员进行了调查，以了解城市自然区域森林的范围和管理。我们发现，城市自然区是占主导地位的绿地土地覆盖物，在2019年美国96个人口最多的城市中，其占城市公园总面积的68％。在五年（2014-2019年）的相同城市中，自然公园绿地减少了4％（15,264公顷）。在市政规模上，大多数城市都在管理森林自然地区，以保护本地物种。在响应我们的在线调查的108个组织和92个城市中，许多不同的管理干预措施正在用于指导森林结构和组成。管理组织将近70％的时间跟踪这些活动及其结果，这为适应性管理提供了强大的数据基础。但是，仍然存在挑战：94％的组织将入侵物种和有限的资金列为主要挑战。超过70％的受访组织还认为缺乏数据和公众对自然保护区价值的认识不足是主要挑战。随着城市着手扩大和改善绿地的工作，保护自然地区的公园地免于开发并应对这些生态系统的管理者面临的挑战是两个非常重要的目标。