A comparison of the trichopteran communities of streams associated with aspen, spruce—fir, and mixed—conifer forests demonstrated significant differences in structure. Though tricophteran species composition in aspen—associated and spruce—fir associated streams was virtually identical, relative abundances of shredder and grazer Trichoptera differed significantly in the two types of streams. The ratio of shredder to grazer trichopteran biomass in aspen streams was °1:17 while in conifer streams, the dominance was reversed with a shredder to grazer biomass ratio of 3:1. The difference in dominance of functional groups in the two types of streams was attributed to the order—of—magnitude greater standing crops of detritus found in the conifer streams. It is hypothesized that the greater accumulation of detritus in conifer streams is the result of habitat modification by logs. Five times the number of logs were found in conifer streams as compared to aspen streams. The greater accumulation of logs in the conifer streams is attributed to lower rates of decomposition of conifer wood. The data suggest a general model for long—term structural change in trichopteran communities of the southern Rocky Mountains and I suggest that these long—term changes result from changes in quantity and quality of wood inputs during forest succession.