Large scale burning of the upstream catchment results in greater and longer lasting effects on stream macroinvertebrate communities than local site scale burning.

Background The increasing frequency, severity and intensity of wildfire globally is generally recognised as a significant threat to freshwater biodiversity. Fires impact streams through a range of mechanisms including geomorphological change, altered resource availability and direct impacts on biota. The magnitude and duration of fire impacts on stream ecosystems vary widely. Reasons for this variation are hypothesised to include the effects of fire can be from upstream catchment disturbance, disturbance at the site, or both. Additionally, many studies have sub-optimal designs as they are poorly replicated, short term, lack before data, and/or lack unburnt controls, which may further contribute to this variations in impacts. Here, we use a before-after-control-impact (BACI) design in sub-alpine woodlands in south-eastern Australia with 7 years of before data and 8 years of after data, to determine the effects of landscape-scale fires on stream macroinvertebrate community structure at local and landscape scales. Results Catchment scale disturbance had greater impacts for a longer duration (up to 4 years) on macroinvertebrate communities than local site scale disturbance (up to 1 year). Fire-induced changes in in-stream habitat and resources (e.g., substrate composition) were associated with the greatest changes in macroinvertebrate communities. Macroinvertebrate diversity was lower post fire at burnt sites and catchment burnt sites because of both reduced taxa richness and increased evenness. Differences between burnt and unburnt sites were predominantly a consequence of changes to the abundances of Coleoptera and Diptera taxa. Recovery in macroinvertebrate communities, including those downstream of fire, was associated with recovery of riparian vegetation cover at burnt sites. Conclusions Larger scale disturbance to the upstream catchment was more important for the macroinvertebrate community than local site scale disturbance. Post-fire management to minimise and ameliorate fire effects on stream macroinvertebrates should focus on limiting the downstream effects of fire on in-stream habitat caused by sediment movement and geomorphic changes.