Exotic shrub invasion in a montane grassland: the role of fire as a potential restoration tool

In recent years, invasion of native grasslands by exotic woody plants has been recognized as a global problem with multiple adverse ecological and socio-economic consequences. Reasons for such expansions are numerous, including fire suppression. An important example of this problem is the native montane grassland in the Nilgiris of the Western Ghats in India, a biodiversity hotspot threatened by invasion of multiple woody species. In this study, the impacts of the highly invasive, nitrogen fixing exotic shrub Cytisus scoparius (Scotch broom) on the grassland community and ecosystem function have been quantified and the role of fire as a potential management tool evaluated. I established paired plots in uninvaded and broom-invaded grasslands that were either unburned or burned by an unplanned wildfire event. Invasion negatively impacted the grassland community structure and composition, favoring shade tolerant and weedy native plants, but did not greatly alter ecosystem function. Burning broom patches to eliminate the stands resulted in lower soil moisture and nitrogen levels 18 months after the fire. Yet, there were no notable fire effects on the grassland communities or ecosystem properties. Taken together, the results suggest that fire might be an effective tool for broom control. At the end of the study period burned-broom communities did not become more similar to uninvaded-grasslands; presumably the recovery process may be slow without additional management intervention.