Post-wildfire recovery of invertebrate diversity in drought-affected headwater streams

As climate change progresses, large (> 400 km2) fires are becoming more frequent across many biomes, often in association with intense drought. We analysed 5 years of stream macroinvertebrate data, collected before and after a wildfire that burnt > 750 km2 of the Grampians National Park, Australia. The wildfire occurred in 2006, during a 12-year drought (1997–2009). We tested the hypotheses that wildfire alters macroinvertebrate assemblage composition, and reduces taxon richness and among-stream variation. Five burnt and five unburnt headwater stream reaches were compared before and after the fire; a larger number of reaches were used to examine temporal trends in taxon richness. Wildfire altered macroinvertebrate assemblage composition and reduced among-stream variation in assemblages, but was not associated with low reach-scale taxon richness. Fire was associated with increased abundances of predators specialised for soft-sediments, and with reduced abundances of shredding and algal grazing caddisflies. In the short term, suspension feeder abundances increased, overwhelming the negative effects of drought on their abundance. Within 2 years post-fire, assemblages in burnt streams were similar to unburnt streams; within 3 years, among-reach variability in assemblage composition among burnt streams resembled that in unburnt streams. Invertebrate assemblages recovered rapidly in these streams despite the large areal extent of the fire. However, the frequency of wildfires is increasing, potentially permanently altering riparian vegetation structure and composition. As headwater streams depend on riparian vegetation for shading, woody debris and leaf litter, such permanent changes will likely affect biodiversity in headwater streams.