Mangrove forests associated with salt flats: a case study from southeast Brazil

Abstract In this study, forest structure variability of a mangrove associated to a salt flat in Sepetiba Bay (SE-Brazil) was assessed. Forest structure and interstitial water salinity were measured in 32 plots established along three transects ranging from the margin of the estuary to the transition with the salt flat. Structural development was shown to be highly variable, with mean height ranging from 0.54 m to 7.96 m, mean diameter ranging from 1.58 cm to 9.46 cm and trunk density ranging from 2,733 live trunks.ha-1 to 106,667 live trunks.ha-1. Forest structure variability responded to the gradient of increasing interstitial water salinity towards the salt flat, with mean height and diameter decreasing and trunks density increasing progressively in the same direction. The following pattern of species dominance was observed: Rhizophora mangle near the estuary margin; Laguncularia racemosa at the transition with the salt flat; and Avicennia schaueriana on intermediate zones. The assessment of structural characteristics of mangrove forests and their relationships with natural stressors (e.g., salinity) contribute to better understand the dynamics of the species along coastal plains associated with preserved salt flats, such as the one found in Guaratiba.

摘要 本研究针对巴西东南部塞佩蒂巴湾（Sepetiba Bay）一处与盐滩（salt flat）伴生的红树林，开展了林分结构变异性评估。研究沿三条覆盖河口边缘至盐滩过渡带范围的样带布设32个样地，并测定了样地内的林分结构与间隙水盐度。结果显示，林分结构发育程度存在极高变异性：平均树高介于0.54米至7.96米之间，平均胸径介于1.58厘米至9.46厘米之间，活树干密度介于2733株·公顷⁻¹至106667株·公顷⁻¹之间。林分结构变异性随向盐滩方向间隙水盐度升高的环境梯度产生响应：沿该方向，平均树高与胸径逐渐降低，而树干密度则逐步升高。研究观测到如下物种优势度分布格局：河口边缘近岸为美洲红树（Rhizophora mangle），盐滩过渡带为拉贡木（Laguncularia racemosa），中间地带为舒尔海榄雌（Avicennia schaueriana）。对红树林结构特征及其与自然胁迫因子（如盐度）之间关系的评估，有助于更深入理解物种在与原生盐滩伴生的滨海平原（如瓜拉蒂巴（Guaratiba）分布的盐滩）上的种群动态。