Do Ecosystem Services Really Decline Under Urbanization? Long-Term Evidence from Seoul’s Green Infrastructure (1978–2025)

Urban green infrastructure is increasingly recognized as a critical buffer against ecological degradation, yet empirical evidence on the long-term stability of ecosystem services (ES) in rapidly urbanizing cities remains limited. Despite widespread assumptions that urbanization inevitably leads to irreversible ecological decline, few studies have quantitatively examined whether ES can persist, or even recover, over multi-decadal time horizons. This study investigates the long-term trajectories of eight urban ES in Seoul, South Korea, across nearly five decades (1978–2025) and eight congressional districts, providing one of the longest temporal assessments of urban ES in East Asia. Using i-Tree Canopy and high-resolution aerial imagery across four benchmark years (1978, 1989, 2010, 2025), this study quantified standardized indicators for carbon sequestration (CSeq), avoided runoff (AVRO), and removal of six atmospheric pollutants (O₃, NO₂, SO₂, CO, PM₁₀, PM₂.₅). Paired-sample t-tests and Cohen’s dz (effect size) were used to assess within-district temporal shifts and the magnitude of ecological change. Results reveal a pronounced period of early ecological stress during rapid industrialization (1978–1989), with negative standardized effect sizes across all services (dz between −0.65 and −0.72). However, these early losses were not sustained. Structural services such as CSeq and AVRO exhibited long-term functional stability, with effect sizes converging toward zero and the 1978–2025 change in CSeq showing no statistical difference (p = 0.784). Pollutant removal services followed an early-decline–followed-by-recovery trajectory, exemplified by CO removal shifting from a large early decline (dz= −0.72) to a modest positive effect in later decades dz = 0.31). These findings indicate that Seoul’s sustained urban greening and environmental policies were effective in preventing further deterioration and maintaining core ecological functions, even if they produced stabilization rather than significant long-term gains in ES delivery.