Management regimes for a plant invader differentially impact resident communities

Management of plant invaders causes disturbance and the compounding effects of both invasion and management on biodiversity merit rigorous assessment. We explored the impacts of both plant invasion and management disturbance in coastal dune communities of Australia invaded by the introduced shrub bitou bush (Chrysanthemoides monilifera ssp. rotundata). We compared the effects of intensive, manually based invader control with those of extensive control (mainly herbicide spraying from aircraft) across fore dune communities. We examined one management regime, which was typically intensive, in hind dune communities. Our main aim was to test the prediction that intensive methods would achieve better biodiversity outcomes than extensive approaches in fore dune communities. We found that extensive management created native species complements that diverged from non-invaded sites while intensive management approached non-invaded site conditions. However, intensively managed sites were also richer in other exotic species than extensively managed sites. Thus, while biodiversity outcomes were better under intensive management, the risk profile of such sites was increased by the greater array of exotics that could potentially replace the original invader. The positive effects of management evident on some fore dunes were not found in hind dunes, where managed sites had the highest exotic species richness and similar bitou bush seedling abundance as both non-invaded and bitou-invaded sites. Hind dune managed sites were also compositionally distinct from non-invaded sites. Thus fore and hind dune communities exhibited different responses to bitou management regimes.