Background. Recurrent anthropogenic fire threatens the integrity of Madagascar’s seasonally dry tropical forests, particularly nutrient-poor white-sand systems that are structurally fragile and species-rich. Aims. To quantify the short-term effects of first and repeated burns on forest structure, species diversity, and composition. Methods. We compared three adjacent areas in Ankarafantsika National Park with contrasting fire histories: unburned control, once-burned (2021), and twice-burned (2017 & 2021). Each area contained 21 systematically placed 5 m × 5 m plots. All live woody stems with a diameter ≥ 1 cm were identified and measured. Key results. Relative to the control, stem density declined by 83 % (once-burned) and 89 % (twice-burned); maximum stem diameter decreased from 30.8 cm to < 23 cm. Species richness fell from a median of 33 to 8 and 1, and Shannon diversity from 3.12 to 1.91 and 0.64, respectively. Multivariate analyses showed significant compositional divergence, with twice-burned plots exhibiting the greatest heterogeneity. Canopy dominants were lost from twice-burned interiors, replaced by disturbance-tolerant shrubs and lianas. Conclusions. Even a single fire can cause structural and compositional simplification; repeated burns intensify these effects. Implications. Targeted fire prevention and restoration are essential to conserve biodiversity and maintain resilience in fire-sensitive white-sand forests.
Keywords: Anthropogenic fire; Repeated burning; White-sand Forest; Madagascar; Forest structure; Species diversity; Community composition; Importance Value Index