Response of Small Mammal Mycophagy to Varying Levels and Patterns of Green-tree Retention in Mature Forests of Western Oregon and Washington Katherine M. Jacobs Department of Forest Science Oregon State University Corvallis, OR 97331-5732

Abstract from M.S. Thesis (2002)

The Demonstration of Ecosystems Management Options (DEMO) study is a large-scale, multi-year, interdisciplinary project examining the effects of various levels and patterns of green-tree retention on multiple forest features. Six retention levels and patterns were examined and replicated across six blocks of predominantly Douglas-fir forested land in western Oregon and Washington. As part of the DEMO study, this research focuses on the effects of these silviculture activities on small mammal mycophagy. The diets of three small mammal groups were examined: squirrels (the northern flying squirrel, Glaucomys sabrinus), chipmunks (Townsend’s chipmunk – Tamias townsendii, and the Siskiyou chipmunk – T. siskiyou), and voles (the western and southern red-backed voles – Clethrionomys californicus and C. gapperi). These animals are vital fungal spore dispersers and forest prey. Fecal pellet analysis was used as a non-lethal method of examining the diets of these mycophagous mammals. Fecal samples were collected from these animals before and after the application of treatments. Pre-treatment diet data was utilized for a diet comparison among the animal genera. The change in the frequencies for the common truffle genera, plant material, and total cumulative number of genera were compare using an analysis of variance to measure the effect of each treatment on the diets of the study animals.

Truffle spores from fecal pellets

The pre-treatment fungal diets of the study animals showed significant differences among genera. Glaucomys sabrinus fecal samples contained higher frequencies of Gautieria and Leucogaster spores than either Clethrionomys or Tamias samples. The diet of the Tamias spp. contained higher frequencies of plant material than G. sabrinus or Clethrionomys, emphasizing the more diverse diet of this animal genus. G. sabrinus samples contained the highest mean number of truffle genera per sample and consistently contained a high frequency of the four common truffle genera. Moderately high frequencies of the common truffle genera were common in the Clethrionomys samples. Only the genus Rhizopogon was commonly found in high frequencies in the Tamias samples. The frequency of Rhizopogon spores was consistently greater than 95% in the pre-treatment diets of all animal genera.

Rhizopogon evadens	Gautieria monticola

Treatment effects were found for different diet items for each animal genus. The mean total cumulative number of truffle genera in the diet of the study animals showed little change. The harvesting of trees appears to negatively affect the frequency of Rhizopogon spores in the diet of Clethrionomys, potentially reflecting the reduced ability of these animals to forage for Rhizopogon truffles and a reduction in Rhizopogon truffle abundance or frequency, especially in the 15% aggregated retention treatment. The retention of trees in isolated aggregates restricts the movement of Clethrionomys within the treatment and the abundance of edge on the aggregates may further restrict Clethrionomys to the center of the aggregates. Competition would be increased within these aggregates where animals are concentrated and the resource may be even more limited.

In the diet of G. sabrinus, the frequency of Gautieria spores significantly decreased in the 40% aggregated retention treatment and increased in the 40% dispersed retention treatment. The retention of trees in aggregates may limit the ability of G. sabrinus to move and forage between aggregates and into adjacent habitat. However, in the dispersed retention treatments, adequate travel routes are still available and G. sabrinus could forage throughout the treatment and in to adjacent habitat, thus reducing the impact of the reduction of truffle biomass within a stand.
The diet of Tamias spp. showed little change in response to the treatments. The wide diversity of habitats that Tamias utilize may extend the ability of this animal to find and compete for truffles even as they decreased locally, until a large decrease in biomass occurred.

The sporocarp biomass data (D. Luoma, unpublished data) showed that overall truffle biomass declined, whereas consumption of truffles by these small mammals largely stayed the same. This suggests that the animals are compensating for a locally declining food source by altering their foraging behavior. The long term effects of this behavioral compensation on energetics and population dynamics is unknown.