Urbanization destabilizes soil organic carbon (SOC) in urban forests, threatening their long-term function as carbon sinks

Urbanization disrupts SOC stability in forest ecosystems, weakening their vital role as carbon sinks. As cities expand and land-use intensifies, it becomes critical to understand how urban pressures disrupt the underlying mechanisms that stabilize SOC, an essential component of global climate regulation.

A recent review published in Carbon Research by Prof. Xiankai Lu’s team at South China Botanical Garden,Chinese Academy of Science, synthesize how urbanization affects SOC stability in urban forests. Drawing on studies across urban-to-rural gradients, the review identifies three indices of SOC stability: physical (related to soil structure and protection of carbon in soil aggregates), chemical (referring to the chemical forms and binding of carbon in soils), and biological (related to microbial activity and soil fauna), all of which are made vulnerable by anthropogenic disturbance.

The research demonstrates that SOC is most stable in minimally disturbed rural forest soils, whereas urban forests experience substantial losses of critical SOC fractions needed for long-term carbon sequestration. This pattern is further explained by changes in biological stability and microbial biomass carbon (MBC), which decline in urban forest soils. In addition, we showed how urbanization influences the formation and stability of SOC across forest ecosystems along an urban–rural gradient (Figure 1).

The review further shows that frequent urban disturbances disrupt important stabilization pathways. These include the binding of organic carbon to iron (Fe) and aluminum (Al) oxides, which typically protect SOC from microbial decomposition (Figure 2). The review also emphasizes that in urban forests, human-induced stressors such as atmospheric pollution, fragmented landscapes, altered microclimates, and degraded soil structure are the dominant drivers of SOC dynamics. This contrasts sharply with rural forests, where SOC stability is largely regulated by natural processes like litter input, root turnover, and hydrological conditions. Given the accelerating pace of urbanization and climate change, it is imperative for researchers, policymakers, and urban planners to prioritize focused studies and targeted interventions that protect soil carbon and enhance climate resilience in cities.

The review, titled "How urbanization reshapes soil organic carbon stability in urban forests: a critical review," was authored by Lasisi Hammed Tobiloba, a current PhD student at South China Botanical Garden, CAS, with LU Xiankai serving as the corresponding author. This work was supported by the National Key R&D Program of China, the Guangdong Provincial Key R&D Program, and the National Natural Science Foundation of China. Link: https://doi.org/10.1007/s44246-025-00230-8

Fig. 1. Concept of the formation and distribution of soil organic matter (SOM) from an urbanization perspective.（Image by LU et al.）

Fig. 2. Impacts of anthropogenic disturbances on soil organic carbon (SOC) fractions and the mechanisms by which iron (Fe) and aluminum (Al) oxides stabilize SOC.（Image by LU et al.）

Fig. 3. Influencing factors of SOC stability in rural forest (a), sub-urban forest (b) and urban forest (c).（Image by LU et al.）