Fungal communities in the rhizospheres of oak roots were shown to change after the trees were felled. The ecological significance of this is considered. Fungal communities were isolated from rhizospheres of thin roots (0.5-1 mm diam.) of living trees and their stumps two years after felling in 30- and 50-year-old stands of Quercus robur, with samples taken at two locations in each stand. In total, 128 species of fungi were isolated. Six species, Absidia cylindrospora, Penicillium adametzii, P. citrinum, P. daleae, P. janczewskii and Umbelopsis vinacea were detected in the rhizospheres of living oaks and stumps at all locations. The abundance of Geomyces spp. + Pseudogymnoascus roseus, Gymnoascus reessii and Zygomycetes was greater, and of Penicillium spp. was smaller, usually significantly, in rhizospheres of stump roots than of living tree roots. Among Zygomycetes, the populations of A. cylindrospora and Mucor hiemalis decreased, while those of Mortierella spp., particularly M. macrocystis, increased after felling. Species of Penicillium favoured by roots are P. adametzii, P. citrinum, P. daleae, P. herquei, P. janczewskii, P. raistrickii. On stump roots they are replaced by P. chrysogenum, P. islandicum and P. spinulosum. The combination of Chalara spp. with oak roots indicates the occurrence of specific relationships, suggesting that the organic food base provided by the plant is a primary factor determining the composition of the fungal community. Edaphic and other environmental factors may be less important in this effect.