<![CDATA[Background: Reclaiming post-bauxite mining landscapes poses complex challenges owing to severe topsoil loss and drastic chemical alteration, yet phase-specific soil recovery trajectories in tropical Southeast Asia remain poorly characterized. This study evaluates the temporal dynamics of nine chemical properties across a post-bauxite reclamation chronosequence at PT ANTAM UBPB, West Kalimantan, Indonesia. Methods: Soil samples were collected from eight sites, one natural forest control and seven reclaimed plots revegetated between 2014 and 2020 with three replicates per site, yielding 24 composite samples. Parameters encompassed pH, organic carbon, total nitrogen, available phosphorus, exchangeable cations, cation exchange capacity, base saturation, and exchangeable iron. Analyses included Pearson correlation, Principal Component Analysis, and K-means clustering validated by Silhouette analysis. Findings: Recovery proceeded through three non-linear phases: destabilization (5–7 years), transition (8–9 years), and initial stabilization (10–11 years). Soil pH showed the strongest recovery, with a mean recovery index of 109%, consistently surpassing the forest baseline. Iron exhibited the most critical deficit, averaging 19.9% recovery with a nadir of 2.0% at year seven, a micronutrient bottleneck not previously documented in tropical bauxite systems. Organic carbon and total nitrogen retained persistent deficits of 44.7% and 35.0%, respectively. The C–Fe coupling (r = 0.784) confirmed that iron mobilization is organically mediated, while PCA indicated that stabilization-phase soils occupy a distinct geochemical equilibrium separated from the forest reference. Conclusions: Post-bauxite recovery stabilizes into a novel ecosystem state with permanent deficits in iron, carbon, and nitrogen. The transition window at 8–9 years represents the optimal period for organic amendments and chelated iron applications to redirect the trajectory toward functional productivity. Novelty/Originality of this article: Providing the first quantitative evidence that recovery follows a non-linear, phase-dependent pathway converging toward a novel ecosystem state rather than the pre-mining forest baseline.]]>
