Impact of deforestation on mangrove tree diversity, biomass and community dynamics in the Segara Anakan lagoon, Java, Indonesia: A ten-year perspective

Indonesia has the largest area and the highest tree species richness but also one of the highest loss rates of mangroves worldwide. The Segara Anakan lagoon is a mangrove-fringed estuarine system in Java which is highly affected by deforestation, sedimentation, and land-use changes. The spatial variability of diversity, community composition, density, height, aboveground biomass and habitat complexity of the mangrove forest in relation to abiotic conditions was studied in 2014/2015. Vegetation characteristics were compared with those available from 2005/2006, and the effects of deforestation on the forest condition were assessed. In total, 15 mangrove tree species were recorded in 2015, six less than ten years ago. The two main areas of the lagoon, the central and eastern one, had a significantly different tree community composition. The central area was dominated by the palm Nypa fruticans and Aegiceras corniculatum and 74% of the ground was covered by the understorey plants Acanthus spp. and Derris trifoliata. Tree density, stand basal area, species number, aboveground biomass, and habitat complexity were significantly lower in the central area as a result of deforestation. Stand basal area and aboveground biomass decreased significantly over the 10 years as well as the density of Avicennia spp., Sonneratia spp., Ceriops spp., Aegiceras corniculatum, and Bruguiera spp. The eastern area was dominated by A. corniculatum and Rhizophora apiculata, and coverage with understorey plants was only 11%. The density of R. apiculata increased significantly over the 10 years as a result of natural regeneration and reforestation. The overall low tree height (2.8 m) and aboveground biomass (18.4 t dry mass ha⁻¹) point to a young and degraded forest. In the central lagoon, mangrove reforestation is probably extremely difficult due to the strong expansion of understorey plants. It is assumed that ongoing deforestation will cause a further spread of understorey plants, a decrease in species number, tree density and habitat complexity. A decline in microhabitats and aboveground biomass can lead to a decrease of faunal species and biomass which in turn would influence nutrient cycling and impair the nursery function of the area. Also, important ecosystem services, particularly coastal protection against storms and prevention of coastal erosion are most likely affected.