Contrasting soil seed bank and vegetation dynamics between protected and disturbed arid rangelands in Southern Tunisia

Abstract

Introduction: Over recent decades, accelerated degradation of arid rangelands has led to significant losses in ecosystem function, in some cases surpassing irreversible thresholds that hinder restoration. Soil seed banks (SSBs) serve as critical ecological reservoirs influencing vegetation succession and ecosystem resilience after disturbance.Methods: This study investigates the effects of grazing on both above-ground vegetation (AGV) and SSB dynamics. It evaluates the efficacy of long-term protection as a restoration strategy in arid ecosystems. We compared a protected area (a national park) with adjacent continuously grazed rangelands by monitoring above-ground vegetation during the 2022 spring growing season and conducting an emergence test on soil samples collected in summer 2022 at two depths (0–3 cm and 3–6 cm).Results and discussion: Protection substantially increased vegetation cover and improved surface properties, including litter accumulation and the development of biological soil crusts. The protected site supported persistent perennial, medium- to high-palatability species, while grazed areas exhibited higher SSB density and richness dominated by ephemeral, disturbance-tolerant taxa associated with sparse vegetation and highly disturbed soils. Sorensen’s similarity coefficient (SSCI) indicated high similarity between above-ground vegetation inside versus outside protection (0.77), moderate similarity between SSBs (0.62), and a greater decoupling between above- and below-ground components in the protected area (0.43) compared to grazed rangelands (0.57). Despite the similarity in shared species occurring under both management regimes, total vegetation cover, plant density, and species richness increased significantly under protection, highlighting the negative impact of continuous grazing in arid environments. However, when combined with aridity, plant senescence and surface crust formation may create barriers to regeneration and limit the long-term dynamics of both AGV and the SSB under prolonged protection. These findings indicate that both prolonged protection and continuous grazing can diminish regeneration potential and reduce resilience in arid rangelands. Accordingly, controlled grazing regimes that balance disturbance with sufficient recovery periods, coupled with regular monitoring of SSB, are critical for maintaining ecosystem function and resilience. Further research is needed to investigate SSB dynamics under different management practices, particularly at sites where controlled grazing systems are implemented.