Pacific Northwest Research Station

Title: Effects of alternatives to clearcutting on invertebrate and organic detritus transport from headwaters in southeastern Alaska.

Author: Musslewhite, Jake; Wipfli, Mark S.

Date: 2004

Source: Gen. Tech. Rep. PNW-GTR-602. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 28 p

Station ID: GTR-PNW-602

Description: We examined the transport of invertebrates and coarse organic detritus from headwater streams draining timber harvest units in a selective timber harvesting study, alternatives to clearcutting (ATC) in southeastern Alaska. Transport in 17 small streams (mean measured discharge range: 1.2 to 14.6 L/s) was sampled with 250- µ m-mesh drift nets in spring, summer, and fall near Hanus Bay at an ATC installation on Catherine and Baranof Islands. Samples were taken before (1996) and after (1999, 2000) nine timber harvesting treatments were applied. Invertebrate and organic detritus drift densities and community composition were used to assess treatment effects. A comparison of drift densities before and after treatment showed year-toyear differences comparable to natural variation at other sites in this study, but no clear relationship to intensity or type of timber harvest treatments. Natural variation in drift densities prevented detection of any potential timber harvesting effects. Coefficients of variation showed transport was most variable among streams, followed by seasons and then days. A trend toward an increase in the proportion of true flies (Diptera) and a decrease in the proportion of mayflies (Ephemeroptera) was seen in more intensive treatments. Although transport rates were extremely variable, a mean of 220 mg invertebrate dry mass and 18 g detritus per stream per day was being transported downstream. The transport of this material suggests that headwaters are potential source areas of aquatic and terrestrial invertebrates and detritus, linking upland ecosystems with habitats (commonly fish bearing) lower in the catchment.

Keywords: Alternatives to clearcutting, headwater streams, invertebrates, organic detritus, riparian

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Citation

Musslewhite, Jake; Wipfli, Mark S.  2004.  Effects of alternatives to clearcutting on invertebrate and organic detritus transport from headwaters in southeastern Alaska..   Gen. Tech. Rep. PNW-GTR-602. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 28 p