Vietnam’s 2010 GHG inventory mapped national land-use classifications onto IPCC reporting categories. Within ‘forest remaining forest,’ various types of forest are reported, including mixed wood and bamboo forests and plantation forests that might fall within the broader definition of agroforestry. Perennial crops on agricultural land are categorized in the GHG inventory as a form of cropland. The inventory presents a land-use change matrix showing that in 2005, there was 59,260 ha of perennial cropland, which increased to 186,302 ha in 2010, mainly due to conversion of forest land and annual cropland to perennial cropland. This was determined on the basis of land-use statistics from the General Statistics Office of Vietnam, which are reported annually.
To estimate the related carbon stock changes, it was assumed—presumably on the basis of expert knowledge of local perennial systems—that perennial cropland planted in the last eight years had an increasing carbon stock, while perennial cropland more than nine years in age had reached a steady state. Since the area of perennial crop increased continuously from 2002 to 2010, the newly planted perennial crop area is estimated simply from the increased area of perennial cropland within the last eight years, which in 2010 was 611,300 ha. The carbon stock change factors used were based on default biomass growth rates in IPCC (2003). The remaining perennial crop area was assumed to be at a steady state, and no biomass increment was attributed to these lands.
Source: Rosenstock et al. 2018