Invasiveness of Phragmites australis in communities dominated by native species after fire disturbance under controlled conditions

Abstract

Background. Wetlands are heterogeneous and dynamic ecosystems, very susceptible to invasions or local extinctions by the effects of invasive or over-dominant plant species. Resistance to invasion in wetlands that suffer disturbances such as fires has not been thoroughly studied. When Phragmites australis (common read) is present, its interaction with disturbance factors has led to local extinction of many native species. In a previous study, it was determined that harvesting is an effective control method for this species. But removal of aerial parts of this species generates many fragments that might propagate the species. Goals. Evaluate under controlled conditions the invasive potential of fragments of Phragmites australis in plant communities dominated by native plant species that are subjected to frequent human-made disturbances, such as fire, under controlled conditions. Methods. We carried out an experiment that consisted of two assays in 36 mesocosms with canopies of Schoenoplectus americanus. Results. Phragmites australis was practically not able to establish itself after the loss of the S. americanus canopy following fires, because the canopy of this last species recovered rapidly. Survival and growth were slightly higher in mesocosms with low disturbance (27.7% and 55.9 cm in the first assay, and 9.4%, and 60.6 cm in the second assay), when compared with controls (8.5% 35.3 cm, and 7.4% and 86.7 cm), because in control units the canopy of S. americanus was a permanent barrier to the development of P. australis. Height differences among burned and control mesocosms after the first fire event were significant (p =0.002) but not after two consecutive years of burning (p =0.085), because the few plants that survived in control units reached considerable height. Conclusions. The risk of establishment of the fragments of Phragmites australis that are generated during harvesting is low even after major disturbances of native vegetation cover.