Forest stand structure and cone crop affect winter habitat use by Eurasian red squirrel (Sciurus vulgaris)

Food resources are one of the important components of high quality habitat. One way to better understand the behavioral decisions made by animals to select foraging patches is focusing on the important forest stand structure characteristics. In this study we investigate the relationship between red squirrel habitat preferences, forest characteristics, i.e. distance to forest edge, canopy closure, cover of understory and undergrowth, and estimated cone biomass. We explore for the first time a methodology to predict cone biomass based on allometric equations and the extent to which this parameter affects habitat choice by red squirrels. Using tree measurements to predicted cone biomass at the plot level which is located in a given stand provides a usefulness proxy of food resources and it is not time-consuming compare with the traditional annual cone count. We selected sixty 30-by-30 m plots in mature Norway spruce forest stands where we measured percentage understory cover, percentage undergrowth cover, distance to forest edge, number of Norway spruce trees, diameter at breast height and height of each Norway spruce tree, number of other tree species and percentage of canopy closure. Within each plot, we counted all Norway spruce cones stripped by red squirrels. Results showed that both forest characteristics (i.e. distance to forest edge and canopy closure) and estimated cone biomass were significant predictors of red squirrel feeding signs on Norway spruce. Our study revealed the potential usefulness of cone biomass as a parameter to determine cone productivity of Norway spruce stands. The effects of food abundance and forest stand structure characteristics are crucial for habitat selection by red squirrels. Estimation of cone biomass based on the tree measurement can be useful for predicting potential foraging habitats for red squirrels regardless of the seed year and can be simple to use for conservation practice in order to locate potential sites for protection of this species.