Igniting river health? Testing the effectiveness of low intensity burns to improve riparian vegetation quality in modified ecosystems

Background Fire is largely untested for controlling invasive exotic plant species in highly modified riparian systems. Aims This study tested a low intensity burn in combination with herbicide application for reducing cover of three riparian woody weeds and increasing the presence of native plant species. Methods We surveyed native and exotic riparian vegetation and three target woody weeds over 1 year at a river reach that underwent herbicide treatment and a low intensity burn. Fire temperatures were recorded at the soil surface and 10-cm depth. Key results Maximum temperatures in burned areas exceeded 399°C at the soil surface and reached 47.1°C at 10-cm depth. Exotic midstorey species richness and woody riparian weed cover were considerably less 3-months after burning and herbicide treatment compared with herbicide treatment alone, then subsequently increased. Conclusions A combination of herbicide treatment with follow-up low intensity burning may be effective in reducing woody weed cover in the short term. However, fire temperatures recorded during the burn may not be hot enough to trigger fire-promoted native species germination. Implications Using low intensity burns in riparian systems to promote native plant regeneration has promise, however, integrated weed management utilising fire in highly modified riparian systems will require follow-up interventions within a relatively short timeframe.