Decoupled vegetation structure and composition in a mangrove–apicum ecotone in Northeastern Brazil

Abstract Mangrove–apicum ecotones are heterogeneous transition zones in which woody colonization need not follow a single age-ordered trajectory. We reanalysed an author-validated area-level matrix from ten successional mangrove patches in the Barra de Gramame estuary, northeastern Brazil. Five patches belonged to a 6–10-year and five to an 11–15-year site-history category inherited from the original survey. Individuals of Avicennia schaueriana , Laguncularia racemosa and Rhizophora mangle were classified into two height-defined structural strata (< 1 m and >1 m) and counted over 225 m2 per patch; a single 900 m2 reference stand was used descriptively. Hierarchical Bayesian modelling, fully enumerated exact permutations, Bray–Curtis and Aitchison analyses, beta-diversity partitioning and leave-one-area-out diagnostics were applied. The <1 m stratum contained 7,439 individuals, compared with 1,898 individuals in the >1 m stratum. Posterior density ratios (< 1 m/>1 m) were 2.73 (95% credible interval: 1.46–5.12) in 6–10-year areas and 3.64 (1.94–6.73) in 11–15-year areas, whereas site-history effects remained uncertain. Abundance-sensitive assemblage structure differed significantly between height strata (Bray–Curtis R2 = 0.213, exact P = 0.00195), whereas relative species composition did not clearly differ under Aitchison geometry (R2 = 0.029, P = 0.105). Abundance gradients accounted for 96.1% of paired Bray–Curtis dissimilarity, and areas in the older site-history category were not consistently more similar to the reference stand. The ecotone therefore showed a marked height-structure imbalance without equivalent proportional species turnover, while the two coarse site-history categories did not define discrete compositional states. These cross-sectional results support multidimensional, site-specific monitoring and do not by themselves demonstrate a temporal successional trajectory.