Leaf-litter decomposition and macroinvertebrate communities in boreal forest streams linked to upland logging disturbance

Leaf-litter decomposition and associated macroinvertebrate communities were compared in standardized leaf packs across forest streams in recently clearcut (n = 9) and reference (n = 12) low-order catchments on the Boreal Shield in northeastern Ontario, Canada. Logging was conducted under best management practices that included application of 30- to 100-m-wide no-harvest buffer zones on both sides of each stream. No significant differences were detected between sites in logged and reference streams for any reach- or catchment-level characteristics (except % area logged) or water-quality variables. Coarse-mesh leaf-pack mass loss was significantly lower (t-test, p = 0.003), and the ratio of fine-mesh to coarse-mesh leaf-pack mass loss was significantly higher (t-test, p = 0.008) in logged than in reference streams, but no difference in fine-mesh leaf-pack mass loss was detected between logged and reference streams. A stepwise multiple regression model of coarse-mesh leaf-pack mass loss on 15 reach- and catchment-level characteristics indicated that only logging presence/absence (r = -0.524) and average reach velocity (r = 0.397) were significantly and independently associated with leaf-litter decomposition. Macroinvertebrate communities on leaf packs in logged streams were different from those in reference streams. Taxonomic richness was significantly lower in logged than in reference streams. A multivariate ordination and analysis of similarity separated logged from reference streams, and abundances of the 3 most discriminating taxa were significantly lower in logged than in reference streams. A multivariate BVSTEP routine indicated that macroinvertebrate community structure was most strongly associated with logging presence/absence among the suite of site characteristics. Leaf-litter decomposition and aquatic macroinvertebrate community structure were successful bioindicators of catchment logging impacts, even when logging was conducted under best management practices. Effects on litter decomposition and leaf-pick macroinvertebrate communities seem to have been caused by upland logging disturbances because riparian areas were undisturbed in logged catchments.