Event Title

Effects of a Single Grazing Event by Cattle on Terrestrial Invertebrates Falling Into Streams and Trout Populations: Results of a Field Experiment

Presenter Information

Kurt Fausch
Carl Saunders

Location

Eccles Conference Center

Event Website

http://water.usu.edu/

Start Date

3-29-2011 1:00 PM

End Date

3-29-2011 1:20 PM

Description

Recent research has shown that terrestrial invertebrates are important prey resources for trout, often providing about 50% of their annual energy and having strong effects on growth and abundance. However, the importance of this prey resource in rangeland streams has received little attention, and there has been no experimental test of whether riparian grazing by livestock reduces this manual removal of woody riparian vegetation, affect trout populations by reducing terrestrial invertebrate prey in central Wyoming streams. We tested three, short duration (2 - 11 d), grazing treatments: 1) moderate intensity grazing (10-15 cm stubble height), 2) high intensity grazing (5-7.5 cm stubble height), 3) high intensity grazing plus removal of two-thirds of streamside woody vegetation, and 4) a control with no livestock grazing. Overall, short durations of moderate and high intensity grazing had little effect on terrestrial invertebrates entering streams, but grazing plus removal of streamside woody vegetation caused significant reductions in terrestrial invertebrate inputs to streams. In contrast, all experimental treatments reduced the biomass of terrestrial invertebrates in late-summer trout diet. However, these effects did not translate to reductions in trout populations. These results indicate that terrestrial invertebrates falling into streams may be relatively resistant to short, but intensive, bouts of grazing, and that grazing systems that incorporate short grazing bouts and maintain streamside woody vegetation, may also support the terrestrial prey resources necessary to sustain robust trout populations.

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Mar 29th, 1:00 PM Mar 29th, 1:20 PM

Effects of a Single Grazing Event by Cattle on Terrestrial Invertebrates Falling Into Streams and Trout Populations: Results of a Field Experiment

Eccles Conference Center

Recent research has shown that terrestrial invertebrates are important prey resources for trout, often providing about 50% of their annual energy and having strong effects on growth and abundance. However, the importance of this prey resource in rangeland streams has received little attention, and there has been no experimental test of whether riparian grazing by livestock reduces this manual removal of woody riparian vegetation, affect trout populations by reducing terrestrial invertebrate prey in central Wyoming streams. We tested three, short duration (2 - 11 d), grazing treatments: 1) moderate intensity grazing (10-15 cm stubble height), 2) high intensity grazing (5-7.5 cm stubble height), 3) high intensity grazing plus removal of two-thirds of streamside woody vegetation, and 4) a control with no livestock grazing. Overall, short durations of moderate and high intensity grazing had little effect on terrestrial invertebrates entering streams, but grazing plus removal of streamside woody vegetation caused significant reductions in terrestrial invertebrate inputs to streams. In contrast, all experimental treatments reduced the biomass of terrestrial invertebrates in late-summer trout diet. However, these effects did not translate to reductions in trout populations. These results indicate that terrestrial invertebrates falling into streams may be relatively resistant to short, but intensive, bouts of grazing, and that grazing systems that incorporate short grazing bouts and maintain streamside woody vegetation, may also support the terrestrial prey resources necessary to sustain robust trout populations.

https://digitalcommons.usu.edu/runoff/2011/AllAbstracts/2