Seasonal time-series reveal the impact and rapid recovery in richness, abundance and community structure of benthic macroinvertebrates following catchment wildfire.

Catchment wildfire can decimate freshwater benthos when burnt material washes through river channels. We conducted detailed seasonal surveys over the course of one-year at N = 9 sites following summer-time wildfire in 2009 and N = 3 sites following summer-time wildfire in 2010 (constituting one-year time-series of 9 ∗ 5 and 3 ∗ 5 samples, respectively). Basic one-year-on surveys were conducted at an additional 12 sites following 2009 wildfires (Sum:Sum; N = 12 ∗ 2). Burnt sites were compared with 6 reference sites surveyed seasonally between autumn and summer, 2009-2010 (N = 6 ∗ 4), supplemented by 6 additional sites surveyed in summer 2004 (total reference samples: N = 6 ∗ 5). While benthic macroinvertebrates were largely unaffected by the fire event, richness and abundance were decimated during the winter, yet recovered to initial survey levels by the following summer. The differential response of assemblages in the exceptionally wet winter of 2009-10 versus 2010-11 highlighted the catalytic role of rainfall as a driver of benthic disturbance. Ecological disturbance was proportionally greater for less abundant taxa with community evenness peaking at the time of maximum disturbance. Seasonal dynamics in fire-impacted and reference sites followed a similar pattern, implying that despite the major reduction in macroinvertebrate standing crop the general character of benthic processes was sustained. One year after the wildfire event community structure was similar to the immediate post-fire assemblages and generally indistinguishable from reference samples. The statistical importance of habitat parameters at the landscape and local scale (catchment size, landuse, slope, bank management and benthic substrate) were indicative of mechanistic processes underlying wildfire disturbance-recovery and define the scope for mitigation management. The remarkable resilience of community structure in these Mediterranean streams marks an emphatic contrast to the response of benthic macroinvertebrates to comparable disturbance processes in temperate regions. Given the increasing geographic scale and frequency of fires accompanying global warming wildfire-risk may become a leading issue for river management.