Effects of deer abundance on broad-leaf tree seedling establishment in the understory of Abies sachalinensis plantations

Browsing by sika deer (Cervus nippon) has significant negative effects on regeneration in many forests in Japan; however, the effects of browsing on regeneration processes have not been determined quantitatively. Our study was conducted in Abies sachalinensis plantations in seven tracts with differences in deer abundance on Hokkaido, northern Japan, to identify indicators for the effects of deer on the regeneration of broad-leaf species from observing seedlings. Five 5 x 20-m plots were located within each tract, and the densities of seedlings 30-200 cm tall and percentages of browsed seedlings were determined. We used sightings per unit effort (SPUE) by hunters and spotlight survey counts (SLCs) as indices of deer abundance for each tract. Seedling density was negatively correlated with deer abundance and coverage of dwarf bamboo, and basal areas of overstory trees also affected number of seedlings. Percentage of browsed seedlings was positively correlated with deer abundance, and it was affected by deer preferences among seedling species. However, the percentage of browsed seedlings was more clearly related to deer abundance than seedling density. There were few seedlings of tree species a parts per thousand yen100 cm tall in tracts with the highest deer abundance. Based on these results, deer abundances of SPUE > 6 sightings per hunter-day or SLC > 15 animals per 10 km are likely to prevent regeneration of broad-leaf species. The percentage of browsed seedlings and density and browsing damage on tree seedlings a parts per thousand yen100 cm tall are useful indicators of the effects of deer.