Influence of wildfire and harvesting on aquatic and terrestrial invertebrate drift patterns in boreal headwater streams

Abstract

Forested headwater streams are strongly connected to their surrounding riparian areas via the transfer of energy subsidies that underpin instream food webs and, therefore, are highly sensitive to riparian disturbances that influence allochthonous inputs. We compared terrestrial and aquatic invertebrates found in drift across headwater streams in boreal forested catchments with wildfire, harvest with minimum 30-m riparian buffers, and reference catchment histories. Fire-disturbed streams contained significantly greater aquatic invertebrate abundance and biomass compared to reference and harvested streams, but no significant trends were seen for terrestrial invertebrate abundance or biomass. Furthermore, fire-disturbed streams supported distinct drifting invertebrate communities compared to reference and harvested sites, driven by high abundances of the mayfly Baetis and caddisfly Dolophilodes. Aquatic invertebrate drift communities were compositionally dissimilar between fire and harvested sites, but not reference sites and no trends were found for terrestrial invertebrate drift samples. Subtle but detectable differences in drifting invertebrate community metrics, structure, and biomass suggest that the effects of wildfire persist well beyond a decade post-fire in boreal headwater streams. Forest management that emulates natural fire disturbance, including streamside disturbance, may be important for promoting the observed patterns detected in our fire-disturbed catchments.