grazing by fungus feeding invertebrates on fungal mycelium can potentially impact many important ecological processes such as the formation of mycorrhizas and the decomposition of wood and litter. a study was initiated to examine the impact of a fungus feeding nematode (aphelenchoides sp.) on the decomposition of trembling aspen (populus tremuloides) wood blocks under aseptic growing conditions by seven different decay fungi. these fungi were bjerkandera adusta, cerrena unicolor, climacodon septentrionale, ganoderma applanatum, hohenbuehelia grisea, sphaerobolus stellatus, and trametes pubescens. results based on dry weight measurements of wood blocks before and after inoculation and in the presence or absence of nematodes revealed that four of the seven fungi exhibited lower rates of decay in the presence of nematodes. these fungi were t. pubescens, g. applanatum, c. septentrionale and s. stellatus. the other three fungi had slight increases in decomposition of wood blocks in the presence of nematodes. it is suggested that b. adusta and c. unicolor may have responded to grazing by producing enhanced mycelial growth and thus enhanced enzymatic activity. hohenbuehelia grisea is a known nematophagous fungi, capturing and consuming nematodes as a supplementary source of nitrogen, thus accounting for enhanced decomposition in the presence of nematodes.