Evolution of the Sungei Buloh-Kranji Mangrove Coast, Singapore

Abstract The mangroves from Sungei Buloh Wetland Reserve to Kranji Dam represent the largest intact mangrove forest left on mainland Singapore. Mangroves colonized the area around 6820 BP, as sea level rose following the last glacial maximum and a variable thickness of Holocene sands, muds and peats (generally ~1 to >3.8 m thick) were deposited over the pre-transgression land surface. An analysis of a time series of photographs covering the period from 1946 to 2001 has revealed major changes in the distribution of mangroves in the area resulting from development-induced changes in the local hydrodynamic regime and clearance for aquaculture. Mangroves covered 117.3 ha in the study area in 1946 and were actively advancing over the coastal mudflats until 1980. Despite the addition of 6.24 ha from mangrove colonization, the total area covered by mangroves was reduced by ~50% by 1980 due to clearance for aquaculture. Following 1980, a reduction in sediment supply possibly due to the construction of the Kranji Dam, immediately east of the study area, led to the initiation of erosion along much of the coastline, with the mangrove fringe having retreated by up to 50 m in 2001. Establishment of the wetland reserve in 1992 enabled the partial regeneration of mangroves in the area to 86.8 ha, 25% less than in 1946. Three areas of undisturbed old growth mangroves >55 years in age have been identified and are considered to be of high conservation value. Two of these areas are within the current boundaries of the Sungei Buloh Wetland Reserve, but are located along coastal areas that are undergoing severe erosion. The third area is located in the south of the study area, protected from coastal erosion, but outside the current nature reserve boundary and hence is susceptible to loss as a result of future development. This third area is possibly the oldest undisturbed fragment of mangrove forest on mainland Singapore.