中国地方の中山間地域二次林と住民生活に対するニホンジカの影響 : 現状と住民意識

中国地方の中山間地域を対象に，野外調査と地域住民に対するアンケート調査を行い，二次林と住民生活に対するシカ被害の現状とそれを引き起こした要因について考察した。東広島市福富町を調査対象地域とし，ヒノキの大径木と広葉樹が混生する二次林で植生調査を行った。調査区内の14種180本の樹木のうち，3.3%に角研ぎ跡，7.2％に食痕が認められ, 角研ぎに関してはヒノキ，摂食に関してはリョウブに有意な嗜好性が認められた。林床の植被率は低く，不嗜好性植物のアセビが優占していた。シカ被害に関するアンケートでは，「農業被害」が最も多く，この10 ～ 20年で目撃や被害が増加しているという回答が大半を占めた。自由記述では，以前は山の手入れを行っていたが，近年は手が入らなくなったというコメントが多かった。山に入らなくなった理由としては，生活様式の変化のほか，マツ枯れによってマツタケがとれなくなったことをあげる回答者が多かった。以上から，森林利用の停止によってシカの住処となる放置林が増加したが，林内に餌植物が少ないため，人家近くにシカが出現し被害をもたらしていると推測された。

To investigate the impact of sika deer (Cervus nippon) on the forest ecosystem and resident life in a mountainous area of the Chugoku District, we conducted a vegetation survey and an awareness questionnaire survey. The study area was located in Fukutomi-Cho, Higashi-Hiroshima, Hiroshima Prefecture. We set a study plot in a secondary forest composed mainly of Chamaecyparis obtusa and broadleaf trees and recorded the damage by sika deer (herbivory and fraying) on each tree within the plot. There were 180 individual trees belonging to 14 species in the study plot, about 3.3% of which had fraying scars and 7.2% had feeding scars. The analysis indicated that sika deer had a significant preference for C. obtusa as fraying trees and Clethra barbinervis as food. Plant coverage of the forest floor was small and dominated by Pieris japonica, which is known to be unpalatable to deer.
The awareness questionnaire survey revealed that the most common damage by sika deer was crop damage. The survey also indicated that the residents felt that sightings of and damage by sika deer had increased in the last 10–20 years. The residents noted that they had managed their forests for various purposes but stopped the management partly due to lifestyle changes and prevalence of pine wilt disease, which caused a significant decline in matsutake mushrooms. The results suggest that the increase of unmanaged forests provided sika deer with their habitat, and that the deer moved from the overgrazed forests to human habitation in search of food.