Abstract
Fringe mangroves are recognised as a highly valuable resource due to their provision of multiple ecosystem services. However, accelerating human-pressures on mangrove forests are resulting in the loss of key mangrove ecosystem services. In this paper, we assessed spatial–temporal changes in the extent and width of fringe mangroves, and changes in adjacent land use. The study focused on the Kien Giang Province, Vietnam, for the period 1989–2009. The total mangrove extent was estimated at seven points in time using four Landsat TM images (1989, 1992, 2003, and 2006) and three SPOT images (1995, 2003 and 2009). Supervised classification was conducted for image classification and mapping changes using a Maximum Livelihood Classifier approach. Changes in mangrove width were calculated for 2003 and 2009 using the Digital Shoreline Analysis Application.
An assessment of the four Landsat TM images showed a significant decrease in mangrove extent for the periods 1989–1992 (−2.7% yr−1) and 2003–2006 (−2.1% yr−1), while a significant increase in mangrove extent was observed during 1992–2003 (0.7% yr−1). SPOT images were used to classify shoreline land cover into four types, namely mangroves; shrimp farms; built-up areas; and bare and wet ground areas. The total loss of fringe mangrove extent was significantly correlated with the increase in extent of other land covers, especially shrimp farms and bare and wet ground, during the period of 2003–2009.
The overall accuracy assessment of the classification using 2003 and 2009 SPOT 5 images was 90.1% and 90.5% respectively. The overall accuracy assessment of the 2003 Landsat image was 92.1%. This accuracy in classification of mangroves and non-mangroves showed that use of Landsat images was adequate for assessing spatial–temporal mangrove dynamics when higher spatial resolution satellite images were limited. The results highlight the dynamic nature of fringe mangrove communities in the region, and provide data useful for informing shoreline mangrove rehabilitation, conservation efforts, and national monitoring programs for estimating mangrove values of carbon sequestration and shoreline protection functions in Vietnam.
► We quantify the spatial–temporal changes in coastal mangroves associated shoreline land-uses. ► We identify the main drivers of changes in coastal mangroves in relation to the past and present policies on coastal management and land-use change. ► Mangrove deforestation was caused by unplanned shrimp farm and urban development, but suggested the root problem is due to the past inappropriate institutions and regulations. ► A review of policies associated with mangrove conservation is needed.