Mangrove rehabilitation in high erosion areas: Assessment using bioindicators

Abstract

This study identifies a potentially effective rehabilitation technique for implementation in high erosion areas through the use of bioindicators. This is significant given that one third of mangroves have been cleared globally with clearing continuing at a rate of 1–2% per annum. There have been various attempts to rehabilitate degraded mangrove forests, however the success or failure of these is mostly unclear due to a lack of assessment. The two rehabilitation techniques assessed in this study were a basic fence system and another more elaborate fence technique designed by the Kien Giang Biosphere Reserve Project (KGBRP), Vietnam. The assessment was conducted by comparing vegetation and faunal communities in rehabilitation areas to those in adjacent old-growth areas. The indicators included: tree and understory plant diversity and density; forest cover and the density of crabs, mudskippers and gastropods. The results show the KGBRP rehabilitation fence technique delivered tree diversity, plant diversity, tree density and forest cover that most closely resembled old-growth areas. This suggests that the additional protection provided by the KGBRP fence was instrumental in achieving these results. In terms of total mudskipper, Boleophthalmus spp., Periophthalmodon spp. and ocypodid crab density, the KGBRP rehabilitation was most similar to the old-growth areas. This similarity is thought to be related to the comparable forest cover at these sites. The density of large crab holes was much higher in old-growth areas than in basic or KGBRP rehabilitation areas. The disparity between large crab hole density at KGBRP rehabilitation and old-growth areas, despite similar levels of forest cover, is thought to be linked to the immaturity of the KGBRP rehabilitation sites. As the KGBRP rehabilitation is most similar in terms of vegetation and faunal communities to the old-growth areas, it appears to be the most successful rehabilitation.