Forest expansion has been observed in China over the past decades, but the typically applied coarse resolution satellite data does not reveal spatial details about China’s forest transition. By using three decades of satellite observations at a 30-m spatial resolution, we reveal here the complex spatiotemporal patterns of individual forest stands forming the forest return history of southern China. We calculate forest age, forest densification rates, and annual forest fragmentation and show that the observed forest area surge around 2010 is a result of trees planted after 2000 that formed dense forests about a decade later. We document that old forests in the 1980s were mostly fragmented into scattered patches located on mountain tops, but forests rapidly expanded downhill by 729,540 km² and alleviated the clear-cut and logging pressure from old forests. Our study provides a detailed documentation of forest densification and expansion for a country that had been largely deforested three decades ago.