Trophic basis of production of stream detritivores shifts with reduced forest inputs

Estimating changes in organic matter flow from resource to consumer using trophic basis of production (TBP) is a way to examine resource limitation effects on ecosystem function. We examined diet shifts and production of insect detritivores to assess changes with reduced detrital inputs to a forested headwater stream. Organic matter was excluded for 7 years using a canopy net. Small and large wood were removed from the stream after the 3rd and 5th year, respectively. Detritivore production declined after 3 years of litter exclusion. After wood removal, production of detritivores declined again. Steepest declines in Pycnopsyche gentilis production occurred within year 1. Tipula spp. and Tallaperla spp. production declined after wood removal. Diets shifted from leaves to wood to fine particulate organic matter (FPOM) for Tipula spp. and Tallaperla spp., but not for P. gentilis. Resource flows to detritivores shifted in the exclusion stream from leaves to wood to FPOM after leaf standing crops declined and wood removal. Small wood was an important food resource. TBP results showed shifts in food resource use by two detritivores with terrestrial input reduction. These findings suggest that maintaining diverse riparian inputs of organic matter is important for detritivore productivity in forested headwater watersheds.