Microfungus communities of white spruce and trembling aspen logs at different stages of decay in disturbed and undisturbed sites in the boreal mixedwood region of Alberta

Fallen logs of trembling aspen (Populus tremuloides Michx.) and white spruc e (Picea glauca (Moench) Voss) at various stages of decomposition were samp led from undisturbed and 1-, 14-, and 28-year-old post-fire and post-harves t sites in northern Alberta and studied for differences in the associated m icrofungus communities. Wood samples were plated directly onto each of six different media and, from these, fungal species were identified and enumera ted over a 24-month period. Approximately 10 000 isolates were obtained, re presenting 292 species of filamentous microfungi, including 41 ascomycetes, 29 zygomycetes, and 222 mitosporic fungi. The most commonly isolated speci es were Trichoderma viride (Gray) Pers., Rhinocladiella atrovirens Nannf., Penicillium pinophilum Hedgcock, and Mortierella ramanniana (Moller) Linnem . Cluster analysis and ordination of microfungus communities in logs showed that the tree species of the log had the greatest influence on the species composition of communities. Fungus community composition was also correlat ed with the stage of decomposition. Species richness was highest in logs fr om undisturbed sites and lowest in logs from the most recently disturbed si tes. Species diversity (Shannon-Weaver) was only slightly higher at undistu rbed sites than at disturbed sites. The most significant environmental fact or was log moisture, which increased proportionately with stage of decompos ition and was significantly correlated with climatic factors.