Fire differentially affects mortality and seedling regeneration of three woody invaders in forest–grassland mosaics of the southern Western Ghats, India

Abstract

Invasion by exotic woody species is a major concern in grasslands worldwide. Woody invasions pose a particularly serious threat to forest–grassland mosaics globally, but the factors influencing the success of woody species in these systems, including the role of disturbances such as fire, are not well understood. In this study, we evaluated the role of fire in influencing mortality and regeneration success of three globally widespread woody invasives, Acacia mearnsii (black wattle), Cytisus scoparius (scotch broom) and Ulex europaeus (gorse) in the montane forest–grassland mosaics of the Nilgiri Biosphere Reserve in the Western Ghats biodiversity hotspot, India. Our results indicate that mortality and regeneration responses to fire are species-specific. Fire-induced adult mortality was highest in scotch broom and lowest in gorse, and high, but variable in wattle. Burning greatly increased the abundance of gorse and wattle seedlings, but only marginally increased scotch broom seedling abundance. Fire effects on invasive seedling densities were most pronounced at the edges of invasive patches. Overall, our results indicate that fires are likely to differentially affect invasion patterns of these three species, with fire potentially encouraging invasion by gorse and wattle and discouraging invasion by scotch broom.