Seedling germination success and survival of the invasive shrub Scotch broom (Cytisus scoparius) in response to fire and experimental clipping in the montane grasslands of the Nilgiris, south India

The spread of the exotic shrub Scotch broom in the montane grasslands of the Nilgiris is one of the major threats to biodiversity and ecosystem function there. It is likely that fire suppression over the past few decades is the proximate cause of expansion of broom populations. This study capitalizes on a wildfire event to examine fire effects on mature broom populations and soil seedbanks. Fire resulted in widespread death of mature broom stands but also stimulated broom soil seedbanks. However, this initial difference in seedling densities in burned and unburned plots was lost over time due to continuous recruitment in unburned plots. In a seed addition experiment, plots which were clipped prior to the fire showed higher germination success, possibly because fire temperature was moderated by biomass removal. In another experiment, non-dormant broom seeds were added to burned plots, which then received clipping treatments; there were no differences in broom seedling survival in clipped vs. unclipped plots. Overall, these results suggest that prescribed burning might contribute to the control of Scotch broom invasion by helping eliminate mature stands without significantly increasing regeneration from seed.

► We studied fire effects on an invasive shrub, Scotch broom, in a montane grassland. ► Fire killed mature broom stands and stimulated broom soil seedbanks. ► But over time, seedling densities did not differ between burned and unburned areas. ► Our results suggest that prescribed burning might help control broom invasion.