The present study determined the current status of understorey invasive plant species (IPSs) and their impact on the forest composition and regeneration of Palamau Tiger Reserve, Eastern India. Tree diversity was sampled in 63 random belt transects (0.50 ha each), while shrubs and herbs in 9 random quadrats of 5 m \(\:\times\:\) 5 m and 1 m \(\:\times\:\) 1 m, respectively. A sum of 177 plant species were recorded, of which 18 were IPSs with the predominance of the members of the family Asteraceae (7 spp.). In the shrub layer, IPSs contributed the highest density (~ 52% of the overall density), and their contribution in the herb layer (~ 30%) was also very promising. On the other hand, 2% of the forest patches in the shrub and 3% in the herb layer, showed equal distributions of tree saplings and seedlings with IPSs. In contrast, the majority showed an inversely proportional relationship. In the shrub layer, the diversity index and disturbance index revealed an extremely weak but highly significant negative association (R2 = 0.14; p < 0.01), while in the herb layer, the correlation was extremely weak and insignificant (R2 = 0.001; p = 0.78). Increased IPSs density poses an alarming threat to the growth and regeneration of tree saplings and seedlings as well as the understorey plant diversity. Therefore, there is an urgent need for policy intervention and also to manage and control IPSs to enhance the population and regeneration of important plant species of both economic and ecological significance to achieve the United Nations’ sustainable development goal (SDG)-15.
