As urbanization increases worldwide, investments in nature-based solutions that aim to mitigate urban stressors and counter the impacts of global climate change are also on the rise. Tree planting on degraded urban lands—or afforestation—is one form of nature-based solution that has been increasingly implemented in cities around the world. The benefits of afforestation are, however, contingent on the capacity of soils to support the growth of planted trees, which poses a challenge in some urban settings where unfavorable soil conditions limit tree performance. Soil-focused site treatments could help urban areas overcome impediments to afforestation, yet few studies have examined the long-term (>5 yr) effects of site treatments on soils and other management objectives. We analyzed the impacts of compost amendments, interplanting with shrubs, and tree species composition (six species vs. two species) on soil conditions and associated tree growth in 54 experimental afforestation plots in New York City, USA. We compared baseline soil conditions to conditions after 6 yr and examined changes in the treatment effects from 1 to 6 yr. Site treatments and tree planting increased soil microbial biomass, water holding capacity, and total carbon and nitrogen, and reduced soil pH and bulk density relative to baseline conditions. These changes were most pronounced in compost-amended plots, and the effects of the shrub and species composition treatments were minimal. In fact, compost was key to sustaining long-term changes in soil carbon stocks, which increased by 17% in compost-amended plots but declined in unamended plots. Plots amended with compost also had 59% more nitrogen than unamended plots, which was associated with a 20% increase in the basal area of planted trees. Improvements in soil conditions after 6 yr departed from the initial trends observed after 1 yr, highlighting the importance of longer-term studies to quantify restoration success. Altogether, our results show that site treatments and tree planting can have long-lasting impacts on soil conditions and that these changes can support multiple urban land management objectives.

中文翻译：

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修复对试验性城市森林土壤的长期积极影响

随着全球城市化进程的加快，对旨在减轻城市压力和应对全球气候变化影响的基于自然的解决方案的投资也在增加。在退化的城市土地上植树或植树造林是一种基于自然的解决方案，越来越多地在世界各地的城市实施。然而，植树造林的好处取决于土壤支持种植树木生长的能力，这在一些城市环境中构成了挑战，因为不利的土壤条件限制了树木的生长。以土壤为重点的场地处理可以帮助城市地区克服植树造林的障碍，但很少有研究检查场地处理对土壤和其他管理目标的长期（> 5 年）影响。我们分析了堆肥改良、套种灌木、美国纽约市 54 个试验性造林地块中土壤条件和相关树木生长的树种组成（6 种与 2 种）。我们将基线土壤条件与 6 年后的条件进行了比较，并检查了 1 至 6 年处理效果的变化。相对于基线条件，场地处理和植树增加了土壤微生物生物量、持水能力以及总碳和氮，并降低了土壤 pH 值和容重。这些变化在堆肥改良地块中最为明显，灌木和物种组成处理的影响最小。事实上，堆肥是维持土壤碳储量长期变化的关键，在堆肥改良的地块中碳储量增加了 17%，但在未改良的地块中下降。用堆肥修改的地块的氮含量也比未修改的地块多 59%，这与种植树木的基础面积增加了 20% 相关。6 年后土壤条件的改善与 1 年后观察到的初始趋势背道而驰，突出了长期研究对量化恢复成功的重要性。总之，我们的结果表明，场地处理和植树可以对土壤条件产生长期影响，并且这些变化可以支持多个城市土地管理目标。