ABSTRACTThe condition and incidence of vesicular-arbuscular mycorrhizae ofAcer saccharum(sugar maple) in a natural hardwood forest in the Lower Laurentians of Quebec was examined. The effects of forest fertilization on the mycorrhizae were also studied. Microscopic examination revealed VAM structures which included hyphal coils, vesicles, and arbuscules. Vesicles and hyphal coils were the most frequently observed structures, whereas arbuscules were rarely seen. Seasonal differences in the incidence of vesicular-arbuscular mycorrhizae were observed but these differences were not consistent from year to year. Generally, infection rates were lowest in mid-summer. Fertilization of forest soil with a base cation mixture did not appear to affect either the condition or the incidence of VAM.