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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.

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Land degradation in Borneo, one of the world's richest biodiversity hotspots, is extensive. In East Kalimantan, 5,000,000 ha of land are zoned for surface-mined coal.Deforestation from this mining threatens biodiversity and results in soil degradation, erosion, and polluted runoff, all directly impacting human populations. Revegetation methods developed for temperate forests are commonly used globally for mine rehabilitation. However, few empirical studies of native forest restoration as part of mine rehabilitation exist from wet tropical regions. Here, a chronosequence was established to observe forest succession under leguminous plantations at the PT Singlurus Pratama coal mine in East Kalimantan, Indonesia. Soil and natural regeneration data were recorded from samples of ten 20 × 60-m plots randomly located in plantings aged 2, 7, and, 9 years postmining. Linear models (LMEMs) did not reveal greater soil pH, woody plant diversity, or soil phosphorus and nitrogen in older plantings. Rather, they showed higher soil carbon in older plantings, whereas nitrogen and pH were positively correlated with woody species diversity and abundance.Graminoids were less abundant, but ferns were more abundant in older sites in an ordination analysis. The implications are exotic tree plantations shade-out competitive understory herbaceous species (such as graminoids), opening growing space for other vegetation. However, the establishment of woody species is spatially limited possibly by differences in soil degradation among sites. Our results suggest that planting leguminous trees alone may not be sufficient to restore native forests, and future management should conserve and facilitate the establishment of tropical forest topsoil.