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Increasing afforestation efforts are made in the southeastern Gobi in the Inner Mongolia Autonomous Region of China, where tree and grass coexist. However, afforestation that does not consider climate carrying capacity and afforestation at the cost of grassland reduction have caused more and more drawbacks, although forests are of global significance for preventing dust storm emission. Reconstructions of historical forest and grassland cover, forest-grassland interactions, and drivers are urgently required to test the predictions of ecosystem models that support afforestation. Based on a robust reconstruction method applied to a 19,000-year long pollen sequence from northern China, we show that tree cover peaked during the early Holocene (30.7 ± 12.3%) and gradually declined to 13.2 ± 4.3% during the last two centuries. Temperature, precipitation, and fire drove the postglacial evolution of tree and grass cover, and forest may suppress grassland when tree cover is higher than 13.8%. Our study suggests that a cautious approach should be taken regarding the risks posed by afforestation efforts in the southeastern Gobi. • Reconstruction of tree and grass cover based on random forest model. • Tree cover peaked during the early Holocene (30.7 ± 12.3%). • Climate and fire are the main drivers of tree and grass cover. • Forest may suppress grassland when tree cover is higher than 13.8%. • Afforestation should weigh tree cover and grass cover. [ABSTRACT FROM AUTHOR]