Ectomycorrhizal fungal communities in young forest stands regenerating after clearcut logging.

The effects on the ectomycorrhizal fungal community of clearcut logging, which is used to harvest millions of hectares of ectomycorrhizal forest annually, has been studied for a number of years. Here, we review current knowledge of inoculum sources for ectomycorrhizal fungi in forests and then re-examine earlier studies of ectomycorrhizas on young trees in regenerating stands. We conclude that, taken separately from the effects of site preparation, the major impact of clearcut logging is to change the species composition of the ectomycorrhizal fungal community rather than to reduce the percentage of roots colonized. A thorough examination of site preparation treatments suggests that the changes in fungal species composition are driven by changes in the biology and chemistry of the soil environment after clearcutting as much as they are by loss or change in fungal inoculum. This is an important conclusion because it implies that these new ectomycorrhizal fungal communities are better adapted to the new conditions than the ones in the forest would have been. The shift in fungal species composition and diversity will have implications for seedling establishment and competition. The effects of individual fungi or diverse assemblages of fungi on seedling growth, and effects of changes in the ability of young trees to associate with a common mycelium are discussed. Contents Summary 399 I. Introduction 400 II. Population biology and inoculum potential of ectomycorrhizal fungi 401 III. Ectomycorrhiza development on seedlings regenerating after clearcut logging 402 IV. Which is the most important factor driving changes in the ECM fungal community after clearcut logging: inoculum loss or change in the below-ground environment? 406 V. Possible consequences for regenerating stands of species shifts in ectomycorrhizal fungi 414 VI. Conclusions 416.