The processing of conifer and hardwood leaves in two coniferous forest streams. 1: Weight loss and associated invertebrates

Over the past few years stream biologists have substantiated the idea of HYNES(1963) that most small streams are predominantly heterotrophic. The present status ofour knowledge of stream ecosystem structure and function has been synthesized quitewell by CUMMINS (1974). He divides the stream system into functional groups thatcomprise the biological communities. These groups are identified according to their rolesin processing organic matter, which in small streams is derived largely from terrestrialinputs. The processing of the coarse particulate leaf litter by microbes and invertebratesis of prime interest and is fundamental to understanding detrital processing.
In terrestrial systems the presence of soil animals can be critical in the maintenanceof decomposer systems (VAN DER DRIFT & WITKAMP 1959; MACFADYEN 1961, 1963;NICHOLSON et al. 1966; ANDERSEN 1973; AUSMUS WITICAMP 1974). In stream systemsthe role of invertebrates in the breakdown of leaf detritus is significant (CUMMINS et al.1973; PETERSON & CUMMINS, 1974; SEDELL et al. 1974).
The object of this study was to investigate differences in rates of breakdown ofdifferent leaf species common to the coniferous forest streams of western Oregon andto compare the rates of breakdown between a large and small stream. The role andpossible differences of animal associations in the processing of leaf detritus was alsoinvestigated.