Total cellulase and hemicellulase activities agaist model substrates measured in composted yellow poplar, as a function of composting time. Activities are normalized to solids content of the compost sample and are averaged values from three replicates. Asterisks indicate statistically significant differences from the control (* for p < 0.05; ** for p < 0.01). Fluorogenic model substrates were used for the cellulase assay: MUC, 4-methylumbelliferyl-β-D-cellobioside; MUG, 4-methylumbelliferyl-β-D-glucoside. Hemicellulase assays utilized the respective 4-methylumbelliferyl-β-D-glycosides of the monosaccharides D-xylose, D-mannose, D-arabinose, and D-galactose.