Perceived wildfire risk from hazardous forest fuels across the western US has led to the rapid implementation of fuel reduction operations, including mastication (e.g. forest fuel chipping and chunking). Mastication treatments often double forest floor mass and thickness, which alter soil microclimate and carbon (C) inputs. The objective of this study was to determine plot- and field-scale effects of forest fuel chipping treatments on soil microbial communities and C pools in a Colorado ponderosa pine forest. For the plot study, pine chips were added in March 2004 to replicate plots to achieve treatment depths of 0, 5, or 10 cm of chips on the forest floor. The field study consisted of three treatments established in July 2004: forest thinning with slash removed, forest thinning with slash chipped and spread to ~2 cm depth, and nondisturbed soil. Preliminary studies conducted on these field treatments in 2005 and in the plots in 2006 demonstrated effects of chip amendments on total soil C levels, soil fungal biomass, and microbial respiration activity. In 2007, soil samples will be collected from plot and field treatments for analysis of total microbial biomass, fungal biomass, glucosidase and phenol oxidase enzyme activities, and soil C pools (dissolved organic C, particulate organic matter, and mineral-associated C). We hypothesize that chip amendments to the forest floor will enhance soil fungal biomass, phenol oxidase activity, and subsequently will alter the distribution of soil C between labile and stable fractions.