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Direct estimates of microbial biomass were compared to chloroform fumigation incubation estimates of microbial biomass using samples collected from mesic forest stands. Paired soil samples were collected from ectomycorrhizal mats, which contain visible amounts of fungal material, and from non-mat areas immediately adjacent to the mats but which contain no visible fungal material. As much as 30–50% of the dry wt of soil collected from ectomycorrhizal mats can be comprised of strictly fungal biomass.

Direct estimates of microbial biomass from both mat and non-mat soils were 10–300 times higher than biomass estimates obtained using the fumigation incubation method. Fumigation incubation estimates of microbial biomass showed little seasonal variation, while direct estimates revealed that microbial biomass peaked during both the spring and fall when rainfall and temperatures were optimal and were lowest …