Do exclosures in forests with high deer densities provide cover or food for rodents?

The decline of understory vegetation caused by over-browsing linked to increasing deer density is a serious concern. Consequently, deer-proof fences (hereinafter “exclosures”) are being introduced as a countermeasure worldwide. We aimed to confirm the effect of exclosures by investigating the fall population of wood mice ( Apodemus speciosus and A. argenteus ) and their feeding habits over a six-year period inside and outside exclosures in beech forests in Tanzawa, Japan, where deer are abundant. Accordingly, we captured wood mice inside and outside exclosures in beech forests, including areas exclosured over 20 years ago, and analyzed the feces of trapped wood mice using DNA metabarcoding. The capture rate of wood mice was high in exclosed areas with a well-developed shrub layer. In contrast, the capture rate outside the exclosures, including in traps adjacent to the exclosures, was small, even in good beech mast years when their food supply was abundant, indicating intensive use by mice of areas inside the exclosures. However, the results of the dietary analysis based on fecal samples showed that wood mice used beech frequently in good beech mast years, but they used other tall tree species frequently in poor beech mast years, with low usage of shrubs and herbaceous plants regardless of beech nut abundance. These results suggest that exclosing over long periods in beech forests with declining understory vegetation function provides hiding places for wood mice and that the mice inhabiting these exclosed areas are more dependent on food resources derived from tall trees than those from shrubs. • Wood mice intensively use areas inside exclosures in deer-damaged beech forests. • Exclosed-in areas provide cover for wood mice through recovered shrub layer cover. • Wood mice infrequently use exclosed understory forest vegetation as a food source. • Exclosed understory recovery in deer-damaged beech forests requires over 15 years. • Even 10 m square exclosed areas in overbrowsed beech forests improve wood mice habitat.