森林立地学会誌 森林立地50(2), 2008, 167〜173
Jpn.J.For.Environment 50(2), 167−173 2008
ヒノキの雄花生産量に土壌条件と強度間伐が及ぼす影響
中西麻美*・稲垣善之**・深田英久***・柴田昌三****・大澤直哉*****
*京都大学フィールド科学教育研究センター舞鶴水産実験所・**森林総合研究所
***高知県立森林技術センター・****京都大学フィールド科学教育研究センター
*****京都大学農学研究科
ヒノキ花粉はアレルギーを引き起こす物質であり,ヒノキの雄花生産を減少させる森林管理が求められている。ヒノキの雄花生産に土壌条件と強度間伐が及ぼす影響を明らかにするために,京都府と高知県の土壌条件と林分条件の異なる6林分を調査林分とした。それぞれの林分で2つの調査区を設定し,一方は間伐率50%以上の間伐を行い,もう一方は間伐率25%未満の通常間伐または無間伐の対照区とした。ヒノキの雄花生産量を2005〜2007年の3年間にわたって測定した。気象条件が異なる京都と高知で雄花生産量に明らかな差は認められなかった。2005年の雄花生産量はほとんどの調査区で他の2年間より高い値を示した。豊作年だった2005年には,雄花生産量は土壌CN比が低いほど多い傾向が認められた。一方,2006年,2007年には雄花生産量と土壌CN比に明確な関係は認められなかった。強度間伐区と対照区の雄花生産量に有意な差は認められなかった。強度間伐により個体数が減少しても,残存木や林縁木の個体あたりの雄花生産量が増えたために面積あたりの雄花生産量は低下しないと考えられた。以上の結果,強度間伐はヒノキの雄花生産を抑制する有効な管理手法とはいえなかった。豊作年には土壌条件が良好な林分でヒノキ雄花の生産量が大きいことが明らかとなった。
Asami Nakanishi, Yoshiyuki Inagaki, Hidehisa Fukata, Shozo
Shibata and Naoya Osawa :
Effects of soil properties and high intensity thinning on male
flower production in hinoki cypress (Chamaecyparis
obtusa Endlicher) forests
Pollen of hinoki cypress (Chamaecyparis
obtusa Endlicher) causes allergy and forest management reducing male flower
production is required. Effects of
soil properties and high intensity thinning on male flower production in hinoki
cypress were evaluated. Six forests
were selected having different soil properties and site characteristics in
Kyoto and Kochi prefecture. Within
each forest two study plots were selected; one plot was thinned with strong
intensity (>50%) and the other was not thinned or thinned with ordinary
intensity (<25%) as the control plot.
Male flower production of hinoki cypress was measured over 3 years from
2005 to 2007. Male flower
production was not different between the Kyoto and Kochi sites although the climatic
condition was very different. Male
flower production was higher in 2005 than the other two years in most plots. Male flower production of a mast
flowering year in 2005 was higher where soil CN ratio was lower. By contrast, there was no significant
relationship between male flower production and soil CN ratio in 2006-7. There was no significant difference in
male flower production between control plots and high intensity thinning plots.
Male flower production per unit area would not decrease after strong thinning
in spite of reduction in tree numbers, because male flowers per individual tree
located in or adjacent to high intensity thinning plots increased
substantially. The results suggest
that high intensity thinning is not a useful management practice reducing male
flower production and that male flower production of hinoki cypress is higher
where soil nutrient availability is higher in a mast flowering year.