Relationships between Riparian Cover and the Community Structure of High Desert Streams

Many studies on cool, forested streams have shown that removal of riparian canopy leads to higher incident radiation, blooms in algal and macroinvertebrate populations, and concomitant increases in salmonid abundance. In warm, high-elevation desert streams, however, an open canopy may not increase salmonid density. Our seven study reaches on 3rd-order tributaries of the John Day River in eastern Oregon included riparian areas ranging from denuded, heavily grazed streambanks to intact conifer forest. Average summer solar inputs to these sites varied from 165 to 2230 megajoules/m 2 , and stream temperatures were influenced by the density and extent of canopy. Densities of steelhead trout (Oncorhynchus mykiss) and sculpin (Cottus supp.) decreased significantly with greater incident radiation and higher stream temperatures, although many warm-water cyprinids increased in abundance in unshaded sites. Periphyton standing crops (g ash-free dry mass/m 2 ) closely tracked solar inputs and was, in...