Effects of Light and Forest Floor Conditions on the Initial Phase of Regeneration of Pinus Densiflora Sieb. Et Zucc. in Pine Wilt Disease Forests

27 Mar Effects of Light and Forest Floor Conditions on the Initial Phase of Regeneration of Pinus Densiflora Sieb. Et Zucc. in Pine Wilt Disease Forests

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Abstract

マツ枯れ被害林内において,その植生回復を目指し,アカマツの更新誘導を試みた。調査は岡山県内のアカマツ林(被害林および未被害林)の2カ所で行った。マツ枯れによる被害程度(上層下層の密度)により五つの調査区を設定し,そこに地床処理や下刈処理を行い,播種を行った。その後2年間追跡調査を行い,マツ枯れ被害林内におけるアカマツの更新の可能性を検討した。その結果,マツ枯れ被害が大きく林冠が大きく空いた林分や下刈や地かき処理を行った林床においては,未被害林分よりも実生の発生率や生残率が高く,成長量も大きかった。これは,マツ枯れが起こることにより,林内の光環境が明るくなったこと,土壌の有機物層が除去された場合,水分の吸収が容易になり,根系の乾燥を回避できたことなどが原因と考えられた。よって,マツ枯れ被害林におけるアカマツの更新は,成長初期過程においては可能であるといえた。

English Abstract

We attempted to induce regeneration by seeding in a red pine forest damaged by pine wilt disease. Two red pine forests, were selected in Okayama Prefecture, one damaged and one not damaged, from which a total of five plots were selected. The rate of seed predation, the processes of emergence and growth, and the survival rate of seedlings of Pinus densiflora Sieb. et Zucc. were examined under a range of upper and lower level foliage density and conditions at the forest floor. The ratios of survival to emergence were higher in the damaged forest than in undamaged forest in which upper and lower foliage densities were high, or where the undergrowth had not been cut. Seedling growth was greater in the damaged forest than undamaged one. In terms of forest floor treatments, emergency, survival rate and seedling growth were higher when the litter and organic layer was removed than when the litter and organic layer remained. We believe that pine wilt disease, and the subsequent reduction in foliage density, increases light intensity at the forest floor, and that this supports seedling development, at least in the early growth stage. We conclude that regeneration of forests affected by pine wilt disease is possible.