LEAF-LITTER IN A SONORAN DESERT STREAM ECOSYSTEM

Leaf litter is an important functional component of mesic stream ecosy stems; however, the importance of leaf litter has not been established for streams of the southwestern North American deserts. These streams exhibit many functional and structural characteristics that are the r esult of the pattern and amount of precipitation and whim differ from their mesic counterparts. Our objective was to determine the influence of leaf litter on ecosystem processes of Sycamore Creek, Arizona, a t ypical Sonoran Desert stream, and to compare these results with knowle dge gained from other regions. Patterns of nitrogen dynamics and respi ration during leaf decomposition were similar for leaf packs in Sycamo re Creek and previous studies of mesic streams. Macroinvertebrates in Sycamore Creek colonized natural and artificial leaf packs equally, an d taxonomic composition did not differ significantly between leaf type s, or between leaf pack communities and benthic communities. Shredder macroinvertebrates feeding on leaf material were absent. Leaf litter i nput to Sycamore Creek was low and litter residence time was reduced b y flash floods. As a result, leaves played an insignificant role in te rms of nutrient dynamics, energy flow, and macroinvertebrate assemblag es in this ecosystem. Differences in the role of leaf litter between r egions are attributed to channel and riparian form and to the frequenc y of severe disturbance, which are functions of meteorologic, hydrolog ic, and geomorphic features of the landscape.