Mycorrhizal mushroom diversity and productivity—an indicator of forest health?

• Introduction : Fruit-body production of mushrooms is not well understood to date as many factors interact with mushroom growth in nature. Weather conditions play a key role, but they do not completely explain the growth and productivity of wild mushrooms. Mycorrhizal fungi depend on photosynthetically fixed carbon produced by their associated trees, and the physiological state of host trees may well drive the growth of these fungi. We raise the question of whether mycorrhizal fungi can be used as indicators for tree health. • Discussion : In the 1980s, a decline in the species richness and abundance of ectomycorrhizal species was observed in Europe, which was then seen as reflecting the degree of forest dieback. An analysis of the results of a long-term study over 32years in the fungus reserve La Chanéaz confirms this decline: since 1975, the mycorrhizal species have considerably decreased in abundance in relation to the other species. We discuss potential causes of this development and raise questions about a possible relationship between a decrease in mycorrhizal fungi and the health of the associated forest trees. • Conclusion : We do not yet know enough about forest mushrooms to be able to use them as bio-indicators of tree health. More research is needed, especially about the functional significance of ectomycorrhizal fungi on a species leve