Departmental Bulletin Paper スギ人工林における間伐が下層植生の現存量と林床の被覆状態に及ぼす影響について
A preliminary investigation on the effects of thinning on biomass of understory vegetation and floor cover percentage in Japanese cedar plantations

井手, 淳一郎  ,  孫, 昊田  ,  岡部, 憲和  ,  鄭, 聖勳  ,  大槻, 恭一

97pp.11 - 16 , 2016-03-30 , 九州大学農学部附属演習林
間伐が下層植生の現存量と林床被覆率に及ぼす影響を検討するため, 福岡県飯塚市の弥山試験地のスギ人工林において, 間伐後3年が経過した本数間伐率50%と35%の間伐区と林冠が閉鎖した無間伐区のそれぞれに試験プロットを設置し, 主として草本類から構成される下層植生の丈および重量と林床被覆率を調べた。その結果, 間伐率が高くなるにつれて下層植生の生重量と乾燥重量は増加することが示された。また, 間伐区で抽出された下層植生の丈は大部分が50cm以下であり, 最大のものでも86cm であった。これらの結果は, 間伐によって林内の光環境が改善されたことにより丈の低い下層植生の地上部現存量が増加したことを示唆する。林床被覆率についてはいずれの試験区も高い割合(89%~100%)を示したが, 林床要素の構成割合は試験区間で異なった。間伐区では下層植生が, 無間伐区ではリターが林床被覆率に大きく寄与していることが示された。
The effects of thinning on the biomass of understory vegetation and the floor cover percentage (FCP) were investigated in the coniferous plantation watersheds composed of Japanese cedar in the lower slope and Japanese cypress in the upper slope in Yayama district, Iizuka, Japan in 2015. The research sites were set at the valleys of adjacent two thinned watersheds and one non-thinned watershed. Selective thinning of 35% and 50% in number was conducted in the thinned watersheds during January to March in 2012. Fresh and dry weights of understory vegetation increased with increasing rate of thinning in the test sections covered by Japanese cedar. Additionally, the height of understory vegetation sampled in the thinned sections was mostly below 50 cm and 86 cm at a maximum. These results suggest that an increase in aboveground biomass of low-height understory vegetation is attributable to the improvement of light environment under forest canopy by thinning. The FCP was high in the all sections (89%-100%) whereas the percentage of each floor element to the forest floor was different among the sections. Our results indicated that understory vegetation and litter mainly contributed to the high FCPs in the thinned and non-thinned sections, respectively.

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