Response of ectomycorrhizal fungus sporocarp production to varying levels and patterns of green-tree retention

Abstract Forest management activities can reduce ectomycorrhizal fungus diversity and forest regeneration success. We examine contrasts in structural retention as they affect sporocarp production of ectomycorrhizal fungi (EMF)—a functional guild of organisms well suited as indicators of disturbance effects on below-ground ecosystems. Our results are from an experiment that tests the biodiversity assumptions behind current guidelines for ecosystem management. Ours is the first study complete with pre-treatment data that examines the effects of silvicultural manipulations on both epigeous (mushroom) and hypogeous (truffle) sporocarp production by EMF. We tested the effects of two patterns (aggregated [A], dispersed [D]) and four levels (100, 75, 40, and 15%) of green-tree retention on standing-crop sporocarp biomass for spring and fall fruiting seasons. This study employed a randomized block design that replicated six retention treatments in three locations (blocks). A total of 150 mushroom taxa and 58 truffle taxa were identified from the sample plots. Before treatment, the total number of mushroom taxa for each treatment ranged from 58 to 72 while the total number of truffle taxa ranged from 22 to 29. The pre-treatment condition was characterized by mushroom and truffle total fall biomass exceeding total spring biomass in two of three blocks. Although experimental units within blocks were selected for apparent similarity, our results show that uniformity of EMF populations in forests cannot be inferred from stand structure alone. During the post-treatment sample period, the number of mushroom taxa detected in the 100% retention decreased by 34% while the number of truffle taxa increased by 20%. The number of taxa was reduced most in the 15%D treatment followed by the 15%A treatment. The 75%A retention treatment showed the least reduction in number of fruiting taxa. After treatment, sporocarp production declined in all treatments, but these effects varied by season and treatment. Sporocarp production was nearly eliminated from the 15%A retention treatment. Mushroom and truffle production were significantly reduced in the 15%D treatment, though spring truffle biomass was maintained at 33% of the pre-treatment value. No treatment effect was detected on the fall mushroom or truffle standing crop in the 40%D treatment. Our results lend support to the use of dispersed green-tree retention in combination with aggregated retention when maintaining sporocarp production is a goal. Such a mix would ameliorate the effects of clearcutting as demonstrated in this study and may maintain higher levels of sporocarp production in the aggregates by reducing edge effects.