Although the microbial degradation of plant cell wall biomass has been studied extensively in various natural and experimental systems, few studies have comprehensively investigated the structural, biochemical and microbial dynamics involved in the natural degradation of biomass feedstocks by composting.  In this study, yellow poplar sawdust, a feedstock representing a fast growing hardwood energy crop, was incubated in rotary microaerobic composters for 27 weeks during which samples were collected at regular intervals.  Surface degradation of poplar chips was observable by ordinary microscopy after 6 weeks composting, with much more substantial decay of biomass occurring after 15-week composting.  Parallel fluorescence-microscopic experiments on the same series of samples using CBM3-GFP (Carbohydrate Binding Module 3 fused to Green Fluorescence Protein) to label exposed cellulose suggest that more hemicellulose and/or lignin were degraded in early stages of composting and that the cellulose in the biomass was thereby progressively more “unwrapped” and exposed, allowing increased access for the CBM3-GFP to bind to the cellulose.  Consistent with this suggestion, we observed that the “cellulase” activities, as measured by assays against fluorogenic model substrates, showed increasing predominance in later stages (24-week) of composting, whereas the measured "hemicellulase" activities were higher in the earlier stages.  More direct evidence for shifts in ratios of functional lignocellulolytic enzymes, as well as of microbial populations during the composting, was provided by molecular biological analyses of related gene expression abundances.  These data lay a foundation for further genomic and proteomic characterization of the dynamics involved in the natural biomass deconstruction process.