Functional, temporal, and spatial complementarity in mammal-fungal spore networks enhances mycorrhizal dispersal following forest harvesting

Animals that disperse plant or fungal propagules following forest disturbances, including timber harvests, play an important role during forest regeneration by dispersing seeds or spores from intact communities to disturbed sites. Determining how complementary or redundant animal species are as dispersers of propagules is key to understanding the stability of dispersal dynamics and informing management practices. Here we examine the functional, temporal, and spatial components of mycorrhizal fungal spore dispersal by small mammals (rodents and shrews) following timber harvest. We tracked the interactions of seven mammal species and 34 fungal taxa composed of two mycorrhizal functional types, arbuscular mycorrhizae (AM) and ectomycorrhizae (ECM), in 11 patch cuts (0.4 ha) distributed across hardwood and mixedwood forest in the northeastern USA. Over a two-year period directly following harvests, we measured the relative contribution of mammal species to spore dispersal using networks that integrated mammal abundance with spore loads in scat. We also measured species-specific microhabitat associations. Mammals were complementary in their dispersal of AM and ECM fungal spores. However, within AM dispersal networks, mammals were redundant, with asynchrony in mammal population fluctuations among years leading to changes in the relative importance of mammal species. Comparatively, ECM fungal spore consumption and dispersal was primarily provided by one rodent species (Myodes gapperi), resulting in dispersal networks that were highly specialized. This indicates that AM spore dispersal is more robust to changes in mammal community turnover compared to ECM spore dispersal. Mammal species varied from having no microhabitat associations to associating with a variety of different forest structure and ground cover conditions, indicating that species play different roles from broadcasting spores widely to depositing spores in discrete locations. By preserving microhabitat characteristics that are associated with small mammals in harvested areas, particularly downed wood and patches of pre-harvest vegetation, forest managers can help maintain dispersal of mycorrhizal fungi.