森林立地 53(1),23〜29,2011

Jpn J For Environ 53(1), 23-29, 2011

 

立木密度の異なるスギ人工林における葉，幹，繁殖器官への乾物分配率

稲垣善之^1,*・野口享太郎²・金子真司¹・橋本  徹¹・三浦  覚¹

¹森林総合研究所・²森林総合研究所四国支所

 

茨城県北部のスギ人工林において間伐区と対照区を３か所ずつ設定し，林分の収量比数と地上部純一次生産と各器官への分配率の関係を明らかにした。地上部純一次生産速度は，６調査区間で1.9倍の差が認められた。地上部純一次生産速度に対する幹，葉，球果，雄花への分配率は６調査区の平均でそれぞれ64.7%，27.3%，3.0%，3.0.%であった。最も小さい収量比数(0.66)を示した間伐区では，幹への分配率が低かった(54%)。他の間伐区では収量比数は0.74〜0.80を示し，幹への分配率が高かった(71〜72%)。対照区では，収量比数は0.86〜0.91を示し，幹の分配率は平均に近い値を示した(61〜67%)。対照区で雄花生産量の大きい１林分を除外すれば，収量比数が小さいほど雄花生産と雄花生産への分配率が高い傾向が認められた。以上の結果より，強度な間伐は雄花生産を促進し，幹成長を抑制すると考えられた。収量比数が0.75程度になるように林分密度を保つことによって幹成長への分配率を高く維持しながら雄花生産の増加を抑制することできると考えられた。

 

Yoshiyuki Inagaki, Kyotaro Noguchi, Shinji Kaneko, Toru Hashimoto, and Satoru Miura : Biomass allocation to leaves, stems and reproductive organs in Japanese cedar plantations with different stand densities. Japanese Journal of Forest Environment 53:23−29, 2011.

Aboveground net primary production and its allocation to different organs were evaluated along the gradient of stand density in three thinned and three control plots at a Japanese cedar plantation in northern Ibaraki Prefecture. The aboveground net primary production rate after thinning differed 1.9-fold among six study plots. The mean biomass allocations to stems, leaves, cones, and male flowers for the six plots were 64.7%, 27.3%, 3.0% and 3.0%, respectively. The plot with the lowest relative yield index had lower allocation to stems (54%). Two other thinned plots had higher allocation to stems (71-72%). Allocation to stems in the unthinned plots had intermediate values (61-67%). By excluding one control plot with high male flower production, allocation to male flowers was higher where the relative yield index was lower. These results suggest that strong thinning promotes allocation to male flowers but

not to stems, and that stand density should be maintained at a certain level as the relative yield index is 0.75 to maintain allocation to stems and inhibit increase in male flower production.

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