Land abandonment in semi-arid regions represents a critical environmental challenge, significantly impacting ecosystem structure and function. This study investigated vegetation dynamics along a successional gradient in the Zagros forests of western Iran, following the abandonment of agricultural lands. Here, we sampled 96 plots across four successional stages: recently abandoned fields (3–4 years after abandonment, RAA), short-term abandonment (10 years, SAA), long-term abandonment (25 years, LAA), and mature forest (FOR). We analyzed species richness, diversity, composition, and applied niche apportionment models to assess species abundance distributions across four successional stages. Results revealed a clear successional trajectory with increasing species richness and diversity, particularly in later stages. This was evidenced by the number of indicator species, which increased from only 1 in SAA to 66 in FOR. Plant community composition differed significantly among stages, with greater similarity observed between LAA and FOR. Early successional stages exhibited higher compositional heterogeneity, whereas later stages displayed increased homogeneity, suggesting increased community stability. For herbaceous species, abundance distributions were best described by the Dominance Pre-emption model, reflecting the competitive advantage for early-arriving species. In contrast, the abundance distributions of woody species in later stages aligned with the Dominance Decay model, indicating increased niche differentiation and reduced dominance. These findings underscore the importance of temporal progression and competitive interactions in shaping successional trajectories. The study highlights the slow and complex nature of ecosystem recovery in semi-arid regions, emphasizing the need for long-term ecological monitoring and adaptive management strategies to support the restoration of degraded landscapes.
