What exactly is "Land-Use Change and Forestry" and why is it sometimes hugely positive (Indonesia) but sometimes hugely negative (China)? Isn't it supposed to be a type of source not sink (you cut trees, you get more GHG)? See the data here.
You are correct that normally you see a net positive value of GHGs from land use change. However, if forests are grown or revegetated, it is considered a sink (and negative GHG value). This paper says that China has undergone a net increase in forest.
The results sections says:
The land-use data derived from Landsat Thematic Mapper (TM) imagery from 1990 to 2010 were used to estimate the spatiotemporal dynamics of land-use and carbon storage change.
Between 1990 and 2010, China experienced a net increase in forestland, farmland, urban land, and other land (sandy land, gobi, saline-alkali land, swampland, bareland, rock and gravel, and other unused land; table S1). The magnitudes of these increases were 1.52 × 106ha (+0.7%), 1.48 × 106ha (+0.8%),6.87 × 106ha (+43.0%), and 11.74 × 106ha (+5.8%), respectively.
Over the last few decades, the Chinese government developed a number of afforestation programs to revert historically forested areas that had previously been converted into farmland back to forest. Programs, such as the Slope Land Conversion Project and the Natural Forest Protection Project, were responsible for the increases in the area of forest in most regions, except Northeast and Northwest China.