Does shelterwood harvesting have less impact on forest floor nutrient availability and microbial properties than clearcutting?

Chemical and microbial properties of the forest floor were measured in 4-ye ar-old shelterwood treatment plots in the montane coastal western hemlock b iogeoclimatic zone of British Columbia, Canada, and compared to those in ad jacent old-growth and 4-year-old clearcut plots. Forest floor pH, exchangea ble Mg, total C and total N concentrations were similar in all three treatm ents. Bray-extractable P was significantly lower in humus from shelterwood plots, exchangeable Ca was significantly lower in humus from clearcut plots , and exchangeable K was significantly higher in humus from old-growth plot s. Indices of available C (basal respiration rate, microbial biomass and me tabolic quotient) were significantly higher in old-growth plots than in the two harvested treatment plots. The relative increase in maximum microbial metabolic rate due to the addition of organic nutrients was significantly g reater in clearcut plots. Principal component analysis (PCA) ordination of humus samples based on C source utilization patterns of microbial communiti es (i.e., Biolog assay) showed distinctive clustering by treatment, althoug h indices of substrate richness, evenness and diversity were the same in al l three treatments. The relative utilization rates of substrates with the h ighest factor loadings on PCA axes 1 and 2 were dissimilar in each treatmen t. We conclude that forest floors can develop under shelterwood harvested s tands to exhibit chemical and microbial properties atypical of either clear cut or old-growth plots.