Interaction of fungal sporocarp production with small mammal abundance and diet in Douglas-fir stands of the Southern Cascade Range

Small mammal population densities are highly variable across forest stands and landscapes. The species composition and abundance of ectomycorrhizal fungi (EMF) may influence the ability of forests to provide suitable habitat for small mammals. Identification and interpretation of changes in the abundance of these organisms, or in their inter-relationships due to experimental harvest, require that we first identify the patterns and potential causes of natural variability in the pre-harvest communities. Pretreatment data were gathered from the Watson Falls block of a green-tree retention experiment to establish baseline conditions. The six experimental treatments that comprise this block lie in two spatially distinct areas that differ in environment and forest composition. The initial variability in EMF, small mammals, and their relationships was documented. Three primary questions are addressed in this paper: (1) Are the abundance and species composition of EMF sporocarps similar between the two areas of the Watson Falls block? (2) How does sporocarp consumption vary among small mammal species and by area? (3) For common truffle genera, is sporocarp biomass correlated with the spore frequency of those genera in small mammal diets? The Watson Falls block was found to have spatial and temporal variation in EMF production, small mammal mycophagy, and small mammal abundance. However, truffles were consistently the primary food item in the diet of all three small mammal species in this study. Small mammals are potentially important agents of truffle dispersal into disturbed areas where EMF are locally extirpated. This study furthers knowledge of the role of small mammal mycophagy in the functioning of forest ecosystems.