Growth and development of mangrove forests overlying smothered coral reefs, Sulawesi and Sumatra, Indonesia

• Published in: Marine ecology. Progress series (Halstenbek) 2008-10, Vol.370, p.97-109
• Main Authors: Alongi, Daniel M., Trott, Lindsay A., Rachmansyah, Tirendi, Frank, McKinnon, A. David, Undu, Mohammed C.
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Coral reefs; Dry seasons; Forest soils; Mangrove forests; Mangrove soils; Marine; Rainy seasons; Sedimentary soils; Soil depth; Soil samples
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps07661

Smothering of many fringing coral reefs in Indonesia has led to mangrove colonization of the overlying soils in a process of human-induced succession. On the islands of Sulawesi and Sumatra, we measured some structural and functional attributes of 4 mangrove forests that have colonized such soil drapes. The forests varied extensively in stem density, above-ground biomass, and in leaf area index. We estimated accumulation rates of above-ground forest biomass of 1.5 to 8.1 t C ha–1yr–1, similar to other mangroves. The ratio of greenhouse C and N emissions from soils averaged 35 compared with an average soil C:N ratio of 38. Soil ammonification was sufficient to meet forest N demand. A value of 1 to 4% of soil C metabolism was involved in dissolving carbonate, with sulfate reduction being the major decomposition pathway. Rapid rates of N₂ loss were measured, but there was no detectable N₂O release. Rates of nitrogen fixation on the soil surface ranged from 97 to 1648 μmol N m–2d–1, but higher rates (860 to 4316 μmol N m–2d–1) were measured on microbial mats covering pneumatophores, suggesting N₂ fixation on above-ground tree parts may balance soil N₂ losses. Rates of forest biomass accumulation related exponentially to rates of soil C and N metabolism, reflecting a close relationship between tree growth and nutrient availability as mediated by microbes in these shallow soils. These patterns are similar to those in other mangrove forests, and illustrate that human-induced change has resulted in a clear shift from reef-dominated to mangrovedominated habitats and functional characteristics in parts of coastal Indonesia.