Stream canopy and its relationship to salmonid biomass in the Intermountain West

Platts, W. S., R. L. Nelson
Publication Year: 
Study sites on streams in Idaho, Nevada, and Utah were used to determine if grazing had an impact on potential relationships between canopy cover, salmonid biomass and livestock grazing. Platts and Nelson also measured light intensity, unobstructed sun arc, and average potential daily thermal input in grazed and ungrazed (rested) portions of each stream. The best overall predictor of salmonid biomass per unit volume was unobstructed sun arc that was significantly and positively correlated with thermal input. Mean estimates of fish biomass per unit volume differed between the Great Basin (sites in Nevada and Utah) and the Rocky Mountain (sites in Idaho) study areas and were better related to stream canopy attributes than biomass estimates based on stream surface area. In the Rocky Mountains, ungrazed sites generally had more canopy cover than grazed sites. In the Great Basin study areas, however, differences in canopy were unimportant and were likely related to local management practices in several cases.
Montana State University

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