Using Melaleuca fences as soft coastal engineering for mangrove restoration in Kien Giang, Vietnam

• We examine the effectiveness of Melaleuca fences as soft coastal engineering solutions.
• Use local materials with traditional/advanced knowledge for mangrove restoration.
• Fences improve survival ability of planted mangrove seedlings in erosion areas.
• Fences accumulate and stably trap weak mud for mangroves to growth.
• Soft barrier Melaleuca fences promote natural regeneration of mangroves.

Planting mangrove is an important work to respond to mangrove loss and erosion, a serious issue and exacerbated from climatic changes in coastal area of the Mekong Delta. However, the previous efforts have repeatedly been unsuccessful because planted seedlings have suffered complete loss due to the lack of protection from wave action and seasonal sediment movement. Two Melaleuca (Melaleuca cajuputi) fences (wave barrier and silt trap fences) were designed and set up for testing their effectiveness in assisting mangrove restoration in the erosion-prone area of the Kien Giang Province. The wave height of the shoreline behind the Melaleuca fence can reduced by 63% compared to the open coast. After 3 years, they retained from 45 to 47 cm of mud inside the fence line. The survival rate of Avicennia alba (62% and 44%) was much higher than that of Rhizophora apiculata (35% and 14%) in both two fenced treatments. Growth rate of Avicennia seedlings was also much higher than Rhizophora in both treatments. There was a significant statistical difference between live seedlings and growth of Rhizophora and Avicennia in the two fenced treatments. Wild seedlings of Avicennia started colonizing the fenced area after 1.5 years of fence construction and regenerated seedling density varied from 2300 seedlings/ha in to 7100 seedlings/ha after 3 years. Species richness of benthos inside 2 fenced areas approached that in the natural forest area 1.5 years after fence construction. The study demonstrates the high potential of using Melaleuca fences to facilitate regeneration of mangrove and improves coastal protection in Kien Giang Province.