Effects of 10 years of fencing under a gap and closed canopy on the regeneration of tree seedlings in an old-growth Japanese fir (<i>Abies firma</i>) forest overbrowsed by sika deer

We report the effects of 10 years of fencing under a gap and under a closed canopy on the regeneration of tree seedlings in an old-growth fir forest overbrowsed by sika deer in the Tanzawa Mountains. We examined tree seedling emergence and growth of 10 major species over 10 years at four plots: inside and outside a deer exclosure under a gap and under a closed canopy (the plots were named “GAPF”, “GAP”, “CCF” and “CC”, respectively). Seedlings of Abies firma, Acer palmatum and Zelkova serrata were noted at all four plots during the initial investigation. Seedlings of five pioneer species emerged in GAPF and GAP, but had showed almost no emergence in CC and CCF. Seedlings of 10 target species showed the greatest tendency toward survival at GAPF among the plots. The survival of six species’ seedlings was significantly higher (p < 0.0487) at GAPF than at CCF. The height of most seedlings was <20 cm at first measurement. After 10 years, the maximum heights of 10 species showed that all species grew taller at GAPF but scarcely grew at the other plots. The height distribution at GAPF showed that pioneer species dominated >150 cm, while A. firma, A. palmatum and Z. serrata were mainly <120 cm. These results suggest that the 10 species were able to survive and grow most successfully in the gap without sika deer and that the construction of a deer exclosure just after gap formation was effective in promoting the regeneration of the overbrowsed forest.