Carbon Stock Calculating and Forest Change Assessment Toward REDD+ Activities for The Mangrove Forest in Vietnam

Abstract

Mangrove forests are one of the main forest types in Vietnam. However, during the last decades, a lot of mangrove forest area has been converted to other land-use types. The objectives of this study are to assess the changes that occurred in the mangrove forests from 1990 to 2010 and to determine a method for carbon-stock calculating for the forests that can be used as the input data for a Reference Emission Levels (REL) calculation. The study was conducted in two different research areas; one was the Quang Ninh province in the north of Vietnam, and the other took place in the Ca Mau and Kien Giang provinces in the south. In this research, the maps of mangrove forests for the periods of 1990, 2000, and 2010 were created by using optical satellite-imagery data. The change matrix was then calculated by overlaying maps of different periods in the forests for analyzing the changes and assessment. Field trips were also taken to each study area in order to verify/adjust the latest classified mangrove forest maps and interview/identify the main causes of land-use changes taking place during these periods. During the fieldwork, a number of sample points were surveyed to collect the number of parameters of mangrove trees. These data are then used for analyzing the relationship between tree height and the HH and HV values of ALOS PALSAR (Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar) data. An allometric relationship between biomass and tree height was also applied for investigating the relationship between aboveground biomass and ALOS PALSAR polarimetric data. Finally, the change in the carbon stock of the forests through all periods was estimated for living biomass, fuel-wood gathering, and other losses by applying the stock-change method. The results of this study were the mangrove forest maps and biomass maps for the years 1990, 2000, and 2010; the changes analysis showed that the forest area is decreasing and that the main cause is the conversion of the forests to aquaculture land, according to the equations/models of biomass estimation for biomass mapping based on ALOS PALSAR data.