ABSTRACTSpores ofGigasporaandScutellosporaspecies predominated in the root zones of three major plant species growing in the barrier dunes extending from northern New Jersey to Virginia. Similarity in edaphic factors, vegetation, daylength during the growing season, and precipitation along a 355 km transect permitted study of the composition of the VAM fungal community in response to temperature. Twenty-three species of VAM fungi were recovered. Dominant species along the transect wereG. gigantea, Acaulospora scrobiculata, andS. dipapillosa.Some species were more abundant in the northern (cooler) regions of the transect and others were more abundant in the southern regions. Average VAM fungal species richness was positively correlated with distance south along the transect and with temperature parameters. Temperature effects on the VAM fungal community may be separated into two components, a direct effect on the fungi and an indirect effect mediated through the host plant. Plots of rank/log Importance Value depicted the structure of the VAM fungal community and were of use in identifying severe habitats where heat stress appeared to be the controlling factor. Dominance by a single fungal species was inversely correlated with distance south and with temperature parameters. It was most pronounced in northern sites and in the root zones of heat-stressedAmmophila breviligulataplants growing near the species' southern limit.