Recommendations to return the historical disturbance regime in an invader dominated community to restore native species are common. This recommendation is implicitly based on the traditional equilibrium model of succession, a model that has been found to explain the dynamics of few natural ecosystems. We argue that the application and/or manipulation of novel disturbances designed explicitly under an alternative stable states model would be more effective for community restoration. Using a field-trial, we manipulated a newly imposed disturbance in Australian pastoral systems (ungulate grazing), to see how changes in disturbance affected the persistence of an invasive grass species, Eragrostis curvula. We excluded and permitted grazing and applied different control measures to kill and reduce the biomass of the invader. We then monitored the response of the community to these treatments over growing seasons characterized by different rainfall patterns.
Results/Conclusions
We found that the control strategy based on traditional equilibrium models, i.e. removing the causal disturbance and killing the invasive grass, was not the most effective option for restoring native plants. This control strategy reduced the abundance of the target invader, but led to a secondary invasion of an exotic forb, Verbena tenuisecta. The most effective control strategy was based on alternative state models and involved manipulating the current disturbance regime to increase pressure on the invader and relieve pressure on the natives. Increased soil nutrients and grazing effectively reduced the abundance of the invasive grass because it was more palatable and prevented the establishment of the secondary invader. This control strategy appears at odds with conservation efforts, because livestock grazing and nutrient addition are associated with the degradation of plant communities worldwide. However, dynamics of the current invader-dominated community have changed; therefore, novel approaches that alter the existing conditions in favor of recruiting the most desirable community are needed, not simply a return to historical conditions.
