There is great interest in the ability of afforestation programs to sequester carbon, improve soil health, and provide other ecological benefits to urban areas. However, the capacity of urban soils to support successful afforestation and sequester carbon is poorly understood. This study quantified soil carbon in a series of experimental restoration sites established between 2009 and 2011 as part of the MillionTreesNYC Afforestation Project in New York City. Soil cores (0–100 cm) were collected at 10 sites and analyzed for total carbon content. Data were analyzed with respect to depth (0–10, 10–30, 30–70, 70–90, 90–100 cm), high (six species) versus low (two species) diversity planting palettes, and afforestation success (high or low). Results were compared with data from regional reference forest, degraded urban sites in New York City, and disturbed and undisturbed sites in other cities. High success afforestation sites had significantly larger carbon pools than low success afforestation sites and degraded NYC sites. We suggest that these differences were created by interactions between initial site conditions that facilitated plant community establishment and growth, which in turn increased soil carbon accumulation. These initial site conditions include land use history that influences soil physical and chemical factors, as well as proximity to existing forest stands. Diversity treatments had no effect on soil carbon levels, but these may need a longer time period to emerge. These results suggest that afforestation may enhance the capacity of urban soils to store carbon compared to urban degraded soils, but that urban soil properties and site characteristics constrain this capacity.

人们对植树造林计划在固碳、改善土壤健康和为城市地区提供其他生态效益的能力方面表现出极大的兴趣。然而，人们对城市土壤支持成功造林和固碳的能力知之甚少。这项研究量化了 2009 年至 2011 年间建立的一系列实验恢复地点的土壤碳，这些地点是纽约市 MillionTreesNYC 造林项目的一部分。在 10 个地点收集了土壤核心（0-100 厘米）并分析了总碳含量。分析了深度（0-10、10-30、30-70、70-90、90-100 厘米）、高（六种）与低（两种）多样性种植调色板和造林成功率（高或低）。结果与区域参考森林、纽约市退化城市遗址的数据进行了比较，以及其他城市中受干扰和不受干扰的地点。与低成功造林地点和退化的 NYC 地点相比，高成功造林地点的碳库要大得多。我们认为这些差异是由促进植物群落建立和生长的初始立地条件之间的相互作用造成的，这反过来又增加了土壤碳积累。这些初始场地条件包括影响土壤物理和化学因素的土地利用历史，以及与现有林分的接近程度。多样性处理对土壤碳水平没有影响，但这些可能需要更长的时间才能出现。这些结果表明，与城市退化土壤相比，植树造林可以提高城市土壤储存碳的能力，