Benthic macroinvertebrate assemblages in five central Idaho (USA) streams over a 10-year period following disturbance by wildfire

The effects of wildfire on benthic macroinvertebrate assemblages of streams in mixed-conifer forest were examined for 10 successive years following th e Mortar Creek Fire of 1979. Changes in burned-catchment streams were evalu ated relative to a paired set of reference-catchment streams. Taxa richness and total abundance tended to be lower in burn than in reference streams b ut to converge near the end of the study; increases in the final years in b oth burn and reference streams were associated with reduced flows due to dr ought. Total biomass and that of the scraper, filterer, and minor functiona l groups usually were greater in the burn streams. Lack of a strong relatio nship of macroinvertebrate metrics with weather conditions showed that fact ors specific to each stream also were influencing the biotic community. Mea n among-year Jaccard similarity was lower for burn than for reference strea ms. Specific taxa responded differently to the effects of fire. Densities o f disturbance-adapted forms (e.g. Chironomidae, Bactis) increased after the fire but not during the drought period of more stable flows at the end of the study; many other taxa showed the opposite response. Adverse effects of wildfire on the biotic community were largely the result of physical chang es in habitat due to increased runoff. Timing and magnitude of effects diff ered widely among streams as a result of differences in stream size, burn s everity, and specific storm or snowmelt events. Though major effects of the fire on the macroinvertebrates dissipated within 7 years, adjustment in th e habitat and biotic conditions still were taking place at the end of 10 ye ar and normal recovery patterns may have been obscured by the drought.