Processing of native and exotic leaf litter in two Idaho (USA) streams

The Russian olive tree (Elaeagnus angustifolia L.) was brought to the weste rn United States from Eurasia during the early to mid-1900s, and has since become a common member of many riparian communities in Idaho. We compared l eaf chemistry and in-stream processing of Russian olive leaves (exotic) and various species of native leaves in one hardwater and one relatively softw ater Idaho stream. Measurements using air-dried leaves showed that Russian olive contained the greatest concentration of nitrogen, approximately 1.6% of the dry mass, whereas the native species each contained less than 1.0% n itrogen. The C/N ratio of Russian olive was < 30, whereas the natives each had C/N ratios greater than 40. Results from the hardwater stream indicated no difference in 30-day loss of AFDM between Russian olive and the native leaves (dogwood and aspen). In the relatively softwater stream, the Russian olive leaves were processed significantly slower than the native leaf spec ies (cottonwood). The results indicate that a replacement of native riparia n trees by exotics, such as Russian olive, may result in slower rates of le af processing in Idaho streams but that the effect may vary among streams. When comparing the processing of native and exotic leaf litter, initial nit rogen concentrations and initial C/N ratios of the leaves did not appear to be accurate indicators of relative decay rates.