<p>Terrestrial ecosystems heavily depend on vegetation, which responds to carbon dioxide (CO₂) fertilization in hot and humid regions. The subtropical humid karst region is a hot and humid region; whether and to what extent CO₂ fertilization affects vegetation changes in such regions remains unclear. In this study, we investigated the degree to which CO₂ fertilization influences vegetation changes, along with their spatial and temporal differences, in the subtropical humid karst region using time-lag effect analysis, a random forest model, and multiple regression analysis. Results showed that CO₂ fertilization plays an important role in vegetation changes, exhibiting clear spatial variations across different geomorphological zones, with its degree of influence ranging mainly between 11% and 25%. The highest contribution of CO₂ fertilization was observed in the karst basin and non-karstic region, whereas the lowest contribution was found in the karst plateau region. Previous studies have primarily attributed vegetation changes in subtropical humid karst region to ecological engineering, leading to an overestimation of its contribution to these changes. The findings of this study enhance the understanding of the mechanism of vegetation changes in humid karst region and provide theoretical and practical insights for ecological and environmental protection in these regions.</p>