The effect of riparian condition on invertebrate drift in mountain streams

Abstract

The effect of stream riparian condition on invertebrate drift was examined in headwater streams of the Torpy River in north-central British Columbia, Canada. Forest harvesting provided the opportunity to examine drift within control streams (i.e., within intact forest), streams with 10 m foliated reserve strips, streams with 10 m defoliated riparian reserve strips, and streams without riparian reserve strips (i.e., clear cut to the stream bank). The density (concentration) of aquatic invertebrates (individuals m -3 ) in the drift was significantly lower in streams with 10 m riparian reserves compared to control streams (P < 0.002), and this effect was stronger when the data were expressed in terms of flux (i.e., individuals m -2 s -1 ; P <0.001). Terrestrial invertebrate drift density tended to be higher in treatment streams compared to control streams and the magnitude and variation of this pattern correlated with the openness of forestry canopy (e.g., clear cut streams > 10 m defoliated > 10 m foliated). There was significantly more aquatic drift in downstream vs. upstream locations of control streams, but this pattern was reversed for harvested streams (P = 0.51) leading to a significant interaction term in the analysis (P = 0.046; which indicates that the upstream-downstream comparison differed significantly between control and treatment streams in this double-control design). These types of changes in the drift of aquatic and terrestrial invertebrates are known to affect stream ecosystems through trophic interactions among periphyton, benthic grazers, and fish. Consequently, both the quantity and quality of riparian reserve strips must be considered for the effective mitigation of forestry practices.

Estimation of forest harvesting-induced stream temperature changes and bioenergetic consequences for cutthroat trout in a coastal stream in British Columbia, Canada

“…However, firm conclusions regarding post-harvest food supply cannot be drawn from these results because terrestrial invertebrates can comprise more than half of energy ingested by fish (Wipfli 1997;Allan et al 2003;Baxter et al 2005). If food supply decreases, as was observed at the Torpy River, central British Columbia (Hoover et al 2007), trout growth may suffer from the combined effects of increased stream temperature and a lack of food (Fig. 6).…”

“…Trout food supply can be altered following harvesting due to increases in primary production (Kiffney et al 2003) or shifts in the amount and sources of food from aquatic and terrestrial sources (Wipfli 1997;Wipfli and Musslewhite 2004;Hoover et al 2007). Therefore, a sensitivity analysis was conducted on the P parameter to explore the potential effects of post-harvest changes in trout food supply for the four post-harvest years.…”

“…Studies that have observed an increase in trout biomass and/or abundance have generally attributed the increase to greater food supply (Hicks et al 1991). However, studies of post-harvest changes in fish food supply have yielded varying results and few have directly linked changes in food supply with fish growth (Wipfli 1997;Hoover et al 2007). …”

A comparison of impacts from silviculture practices and North American beaver invasion on stream benthic macroinvertebrate community structure and function in Nothofagus forests of Tierra del Fuego

“…Habitat alterations due to disturbances such as invasive species and forest harvesting have been shown to be key drivers of change in benthic community structure and function in streams worldwide 8.4 ± 5.0 3.5 ± 6.1 2.4 ± 7.0 0.7 ± 4.9 0.43 0.73 3,18 (Miserendino, 2004;Hoover et al, 2007). We hypothesized that beaver impacts and forestry practices that did not maintain a riparian forest would lead to decreased taxonomic diversity of in-stream benthic communities due to an increase in the homogenization of the substrate (Anderson and Rosemond, 2007).…”

“…On the other hand, in northwestern Patagonia, conversion of Nothofagus forests to pastures has been shown to be a determinant of benthic macroinvertebrate distribution and abundance (Miserendino, 2004). It is also known that similar catchments in the Northern Hemisphere that are free of management or which have large riparian buffers have been found to have greater benthic diversity than areas that have been clearcut in high latitude forests (Hoover et al, 2007). Therefore, determining the impacts due to forest harvesting on sub-Antarctic streams is a needed focal point of conservation research.…”