ABSTRACTInteractions among five species ofTrichodermawere investigated in the laboratory in order to determine whether temperature affected the ability of species to survive on spruce litter in the face of competition from other Trichodermas. Ability of these species to inhibit the growth of competitors was also tested under a range of temperature regimes. Data showed that, in general,T. hamatum, T. koningiiand isolate LP58 were more aggressive and less subject to displacement than wereT. virideandT. polysporum.All species tested were antagonistic towards each other and towardsBotrytis cinerea, but no marked effects of temperature were observed on antagonistic activity. Displacement experiments, however, showed thatT. virideandT. polysporumsurvived better at lower temperatures.These data are discussed in relation to ecological strategies ofTrichodermaspecies. It is suggested thatTrichodermaspecies, though exhibiting some ruderal properties, should more properly be considered as exhibiting a competitive strategy. Within the genus, it is also suggested thatT. polysporumandT. virideare showing stress-tolerant characteristics.