Disturbance gradients reshape biodiversity, structure, and regeneration in Sal (Shorea robusta) forests of Dharmapur National Park, Bangladesh

• Disturbance gradients reduce species richness and diversity in Sal forests. • Stand structure simplifies with declining basal area and tree density under pressure. • Shorea robusta shows resilience, while late-successional associates decline. • Regeneration shifts toward disturbance-tolerant taxa, risking homogenization. • Findings inform disturbance-sensitive management and community-based restoration. Disturbance gradients strongly influence tropical forest dynamics, shaping biodiversity, structure, and regeneration. This study provides the first empirical assessment of disturbance effects on Sal ( Shorea robusta ) forests in Dharmapur National Park, Bangladesh, part of the Indo-Burma biodiversity hotspot. Across 105 plots, species richness declined from 35 in low-disturbance stands to 17 in highly disturbed stands, while Shannon diversity decreased from 2.4 to 2.1. Stand structure was similarly eroded, with basal area reduced by ∼50% and tree density halved. Although regeneration of S. robusta remained relatively resilient, late-successional and shade-tolerant associates declined sharply, indicating vulnerability to disturbance. Ordination analyses revealed significant compositional turnover, with highly disturbed plots dominated by S. robusta and disturbance-tolerant taxa. These findings demonstrate that disturbance simplifies forest structure, reduces diversity, and constrains regeneration of non-Sal species, increasing the risk of long-term homogenization into Sal-dominated stands. Disturbance-sensitive management, enrichment planting of vulnerable associates, and community-based conservation are critical to sustain biodiversity and ecosystem services, while supporting Bangladesh’s forest policy priorities, REDD+ commitments, and the United Nations Sustainable Development Goals.