Forest invasive species (FIS) are exotic/alien species that occur outside their natural adapted ranges and dispersal potential. Some of the alien species become invasive, when they are introduced deliberately or unintentionally outside their natural habitats into new areas, where they express the capability to establish, invade and outcompete native species. The present study is focuses over the encroachment of invasive species in the two different forest communities of the Tehri Garhwal region of Western Himalaya. Data was collected through extensive field survey and quadrat method. High invasion was recorded in the shrub and herb layer of the forest. In tree strata native species are dominant but their recruitment in the form of sapling and seedlings are displaced by the dense thickets of invasives in both the communities. A highest value of ecological indices was evaluated in Pinus roxburghii dominated site as compared to the Quercus leucotrichophora dominated site. Lantana camara, Eupatorium glandulosum, Clematis gouriana, Rosa brunonii, Rubus neivus, Euphorbia royleana etc. are the most destructive Forest Invasive Species (FIS*) of both the forest communities. The present study gives an accurate assessment and understanding of the dynamics of invasives, which is further important for their scientific management and utilization.