Recently, the distributions of sika deer (Cervus nippon) in Hokkaido are expanding and cause severe damage to agriculture and forestry, and heavy impact on ecosystem. Understory vegetation degrade rapidly by grazing if deer density become higher than a certain level and it is difficult to restore them (Akashi 2009). It is important to control deer population before population levels become too high to avoid degradation of vegetation. Our objective is to establish the relative density index of deer, which is effective in low density area.

We established 19 study plots of 200m² or 400m², and surveyed feeding signs on twigs of trees (more than 1cm DBH) and saplings (taller than 0.2m) in each plot during 2008 and 2010. We also examined the growth of marked saplings and recorded their survival/death. The occurrence of browsed twigs on trees and saplings were compared to spotlight count data collected near each plot.

The percentages of browsed trees and browsed saplings (taller than 0.5m) (BI) are significantly related to the spotlight survey index, and it suggests BI are useful indices of relative deer density. The index of browsed saplings is also effective to evaluate the growth and increasing rate of saplings. We discuss the efficiency of BI as a tool for deer population management.