Is smaller necessarily better? Effects of small-scale forest harvesting on stream ecosystems

Abstract

-Knowledge on ecological impacts of forestry practices on aquatic ecosystems relies almost exclusively on data from large-scale forest harvesting, often involving clearfelling of whole stream catchments. To determine effects associated with less intensive and widespread forest management, we examined the responses of headwater streams to small-scale forest harvesting, including riparian zones adjacent to study reaches but corresponding to less than 5% of the catchment areas. Stream reaches running through recently (2-4 years) harvested forest patches were paired with and compared with adjacent reaches bordered by mature broadleaf forest. We determined abiotic stream characteristics, invertebrate community structures and abundances, trout size and population densities, and leaf litter breakdown rates in each of these pairs. Harvested reaches were found to have different channel cross-section morphology and greater invertebrate abundances in leaf packs than mature forest reaches. Shifts in the abundance of common invertebrate predators were also attributed to riparian forest harvesting. Litter breakdown rates and brown trout densities did not show any significant difference between harvested and mature forest reaches across the four site pairs, possibly because of nonlinear responses to post-harvest riparian canopy openness. Managers must be aware that small-scale forest harvesting in stream riparian areas is not without consequences for aquatic ecosystems. Whether natural riparian forest openings, such as caused by tree death and blow-down, have similar effects on stream ecosystems is an important question to address if we are to confirm the usefulness of small-scale forestry and improve forest and stream management schemes.

Linking stream ecosystem integrity to catchment and reach conditions in an intensively managed forest landscape

“…Increased riparian canopy openness from blowdown increased light levels and algal biomass in streams, creating effects similar to riparian harvesting (Lecerf et al. ) and decreased buffer width (Wilkerson et al. ).…”

Forest canopy cover determines invertebrate diversity and ecosystem process rates in depositional zones of headwater streams

“…Litter breakdown rate did not respond consistently to the difference in the forest canopy, and thus, water temperature may not be the main explanation for differences between streams. Our findings are consistent with those of two previous studies which indicated that, in this study region, the rate of breakdown of alder in riffles may vary nonlinearly with riparian canopy cover (Lagrue et al ., ; Lecerf et al ., ). The strong coupling between litter breakdown rate and shredder density (Table ) suggests that invertebrates were directly involved in determining the variation in litter breakdown rate.…”

Ecological opportunities and intraspecific competition alter trophic niche specialization in an opportunistic stream predator

“…However, despite compelling evidence that salmonids are affected by forest management, little is known on the genuine importance of trophic factors in mediating individual‐ and population‐level responses of fish to changes in riparian canopy cover (Mellina & Hinch ; Lecerf et al . ).…”