LAUSR

Abstract Overbrowsing by the explosively increasing deer has a huge impact on forest vegetation in the temperate zone. Although it was expected that, over the years, the decline of forest floor vegetation would lead to a decrease in deer population, such a decline has not been observed. A dietary analysis of deer is necessary to establish the survival mechanisms of deer populations in forests with degraded understory vegetation. This study explores the foraging strategy of sika deer, Cervus nippon, in Ashiu Research Forest, Kyoto, Japan, where the understory vegetation is severely degraded. A total of 177 fecal samples of sika deer were collected during each season and their food resources identified using DNA meta-barcoding technology and local plant DNA database. The results of the DNA meta-barcoding revealed that sika deer depended on non-preferred plants and preferred plants from early winter to spring. From summer to autumn, sika deer mainly feed on preferred plants. In all seasons, the percent cover of preferred plants for sika deer is also scarce in the forest floor. Biomass of preferred plants, such as litterfalls, play a significant role in maintaining the population density of sika deer when the understory vegetation is degraded in the forest habitat. Therefore, the degradation of the understory vegetation might not necessarily lead to a decrease in the population density of sika deer.