Response of the Cache Creek macroinvertebrates during the first 10 years following disturbance by the 1988 Yellowstone wildfires

We evaluated the effects of disturbance on stream benthic macroinvertebrate s at the ecological scales of time, stream size, and burn extent in six seg ments of Cache Creek over the first 10 postfire years. Postfire changes in macroinvertebrate taxa richness, density, and dominant taxa in the burn str eams were significantly different from those in the reference stream. Chiro nomidae and Baetis typically comprised 40-60% of the macroinvertebrate asse mblages of burned streams but only 15-18% of the assemblage in the referenc e site. Coefficients of variation for the 10-year period indicated that ric hness, density, biomass, and Baetis abundance were more variable (1.2-3.5 t imes higher) in the burn streams than in the reference stream and that vari ability in Chironomidae abundance in burn sites increased with stream size. Fire effects were not attenuated progressively with increasing stream size , probably because the proportion of the catchment burned did not decrease. However, similar-sized streams in which 68-71% of their catchments burned were more severely disturbed than those in which only 39-47% burned. Long-t erm effects on the macroinvertebrate community were due largely to the loss of terrestrial vegetation and increased runoff, which caused severe altera tions in stream channel conditions and large-scale bedload movement.