We are assessing the effect of woody logging-debris retention and competing vegetation control on microbial respiration (MR) following clearcut harvesting at two sites in the Pacific Northwest.  At both sites, retention of logging-debris significantly lowered in situ MR during the growing season (April-Sep.) by 10-35% depending on month. Similarly, absence of competing vegetation caused a significant reduction in MR of 20-35% compared to when it was present.  For logging-debris, the results appear to be largely driven by changes in soil temperature which was significantly reduced following treatment.  However, lab incubations and regression analysis indicate that some factor beyond temperature and moisture is influencing the response.  PLFA analysis indicated significant differences amongst logging-debris treatments in microbial community structure and biomass, providing evidence that effects on MR are associated with those variables.  Reduced MR when competing vegetation was controlled was most likely associated with decreased C inputs from competing vegetation, as soil environmental variables were positively influenced in terms of microbial activity (i.e. temperature and moisture increased when competing vegetation was controlled). Laboratory extractions of water-soluble C seem to support this conclusion, as DOC concentrations were approximately five times higher when competing vegetation was present relative to when it was not. The results indicate that variables other than modified temperature and moisture are influencing MR following harvesting at these sites.