In forested headwater streams, ecological processes such as carbon and nutrient cycling, the stream hydrological regime, and the structure of biological assemblages are tightly linked to the surrounding catchment. As such, headwater streams are vulnerable to disturbances within their catchments at various spatial (e.g. reach and catchment) and temporal (e.g. months to decades) scales. Forest harvesting is an example of a disturbance that has been widely linked to changes in the structure and function of biological communities, and changes in stream processes, such as leaf breakdown. This thesis explores the short term (1 year) response of benthic organic matter storage and retention, leaf litter breakdown and macroinvertebrate structural and functional assemblage composition in headwater streams to catchment-scale selective harvesting in dry-sclerophyll forest in north-eastern NSW Australia. This study used a Multiple Before-After Control-Impact (MBACI) design, with five small adjacent equivalent-sized catchments (302-770 ha), three of which were selectively harvested during a commercial forestry operation, with two left as unharvested controls. Riparian vegetation was retained in accordance with licence conditions for Forests NSW. All five streams were gauged, and since 2001 Forests NSW have been collecting data on turbidity, suspended solids, temperature, run off and stream flow. Standing stocks and composition of coarse particulate organic matter (CPOM) were quantified before and after harvesting in all five catchments, with the prediction that stocks would be significantly lower in harvested streams. Mean standing stocks in all five streams were highly variable spatially and temporally, but harvested streams did not differ significantly from control streams in standing stocks of CPOM. Composition of CPOM was consistent across all streams and proportionally dominated by leaves, then small wood and bark. These findings were remarkably similar to values reported from other Australian streams. The results indicate that in the short term (1 year) there were no detectable reductions in CPOM standing stocks or changes in CPOM composition from selective harvesting.