Forest Regeneration with Deer Exclosure Fences in Cool Temperate Deciduous Forests Declining into Grassy Areas

Abstract

To validate the regeneration potential in forests declining into grassy areas due to tree dieback and regulation by deer foraging, the density and height of regenerating trees greater than 30 cm were studied inside and outside deer fences approximately 10-20 years after establishment in declining beech forests in the Tanzawa Mountains. The density of tall tree species inside and outside of the fences at the sites of＞50％, 25-50％, and ≤25％ canopy openness was 750-8,750 and 0-1,500/ha, 4,500-33,250 and 250-5,000/ha, and 2,750-100,750 and 0-3,250/ha, respectively. Subtall species were dominant at the sites with＞50％ canopy openness. The density of tall tree species was low (0-1,750/ha) at sites with Sasa floors. The dispersal distance was shortest for Fagus crenata and longest for Weigela decora. Owing to development in the height of regeneration trees of tall tree species, including short-dispersal species such as F. crenata, the forest canopy is likely to close at the sites with ≤50％ canopy openness. If canopy openness exceeds 50％, the regeneration of tall tree species, including long-dispersal species, is unlikely, resulting in forests dominated by subtall tree species that form windswept scrub forests. Sites with Sasa floors are predicted to become scrub forests or Sasa grasslands. The study suggested that the establishment of a fence is required when the canopy openness is still lower than 50％ to regenerate tall-tree forests in grassy areas without a Sasa floor derived from beech forests declining under the effects of deer foraging and wind.