Supplementary material from China's fight to halt tree cover loss

China is investing immense resources for planting trees, totalling greater than US$ 100 billion in the last decade alone. Every year, China reports more afforestation than the rest of the world combined. Here, we show that China's forest cover gains are highly definition-dependent. If the definition of ‘forest’ follows FAO criteria (including immature and temporarily unstocked areas), China has gained 434 000 km² between 2000 and 2010. However, remotely detectable gains of vegetation that non-specialists would view as forest (tree cover greater than 5 m height and greater than or equal to 50% crown cover) are an order of magnitude less (33 000 km²). Using high-resolution maps and environmental modelling, we estimate that approximately 50% of the world's forest greater than or equal to 50% crown cover has been lost in the last approximately 10 000 years. China historically lost 1.9–2.7 Mio km² (59–67%), and substantial losses continue. At the same time, most of China's afforestation investment targets environments which our model classes as unsuitable for trees. Here, gains detectable via satellite imagery are limited. Conversely, the regions where modest gains are detected are environmentally suitable but have received little afforestation investment due to conflicting land-use demands for agriculture and urbanization. This highlights the need for refined forest monitoring, and greater consideration of environmental suitability in afforestation programmes.