Basin-wide disruption of ecological strategies of woody species induced by a dam breach in Brazil

The Samarco dam breach in Brazil drastically altered soil and water conditions along the Rio Doce, severely impacting riparian vegetation. This study assessed how these environmental changes influenced the functional traits and ecological strategies (CSR scheme) of adult and juvenile woody plants in reference (unaffected) and impacted sites affected by mine tailings deposition. We hypothesized that mining tailings would reduce functional diversity while shifting plant strategies from stress-tolerant to competitive or ruderal. To test these hypotheses, we sampled 168 species across five regions, measuring key traits (wood density, leaf area, specific leaf area, and leaf dry matter content) and calculating functional diversity indices. RLQ analysis was applied to examine the relationship between plant traits and soil properties. In impacted sites, the plant community was less stress-tolerant than in reference sites, with a consistent reduction in community weighted mean (CWM) for S-selection. Regional responses varied: some impacted areas showed an increase in competitive species, others in ruderal, and some in both. In the adult stratum, impacted sites exhibited greater functional evenness and larger CWM leaf area, while reference sites had higher CWM leaf dry matter content and functional divergence. In the sapling stratum, reference sites had greater CWM wood density and functional richness, whereas impacted sites showed higher CWM for competitive and ruderal strategies. RLQ analysis indicated that stress-tolerant species were linked to nutrient-poor soils, while competitive species were favored in tailings-enriched environments. These findings highlight the strong filtering effect of mining tailings, which consistently reduced stress-tolerant strategies across regions and strata, leading to significant declines in functional diversity.