Using high-throughput sequencing to investigate summer truffle consumption by chipmunks in relation to retention forestry

Intensive management of forests for wood modifies forest biodiversity, affecting the composition of plant and animal communities as well as microorganisms such as bacteria and fungi. Ectomycorrhizal fungi (EMF) form mutualistic relationships with trees, but there is evidence that the abundance and diversity of EMF declines under intensive forest management. The dispersal of some EMF, including that of truffles, depends on small mammals consuming their fruiting bodies and dispersing spores through feces. To better understand provisioning of this ecosystem service within intensively managed forests, we applied high-throughput, DNA amplicon sequencing to scat collected from Townsend's chipmunks (Neotamias townsendii) inhabiting retention patches in recently clearcut-conifer stands. Across two summers, we collected 165 chipmunk scat samples from 43 clearcut-conifer stands in the Pacific Northwest (USA). We identified 81 truffle species representing 16 families, which included many rare and uncommon taxa. Retention patch sizes varied from 9 to 222 trees (0.002-0.83 ha) but we did not detect an effect of retention patch size on the richness of truffles in chipmunk scat samples. However, truffle richness was slightly higher in scat samples collected from chipmunks in retention patches compared to individuals sampled in adjacent clearcuts. Furthermore, the abundance of certain truffle species in chipmunk scat varied in relation to retention patch size and location (riparian or upland), suggesting retention forestry practices may influence truffle community composition. Throughout the sampling season, we detected a 44% decline in truffle species richness and a significant reduction in abundance (i.e., sequence reads) for > 50% of common truffle taxa. Our application of high-throughput sequencing of scat effectively captured variation in truffle species consumption by chipmunks. Our results confirm that common small mammals play an important role in the dispersal of EMF across recently logged forests (<8 years since harvest) and indicate that retaining relatively small (similar to 10 tree) green-tree patches may promote truffle dispersal by providing small mammal habitat.