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We compared the effects of tree size and the basal area of neighboring trees on the growth rate and mortality of individual trees over the past 30 years (1984-2014), before and after the increase of a... sika deer population in a mixed conifer-broadleaf forest in the Shiiba Research Forest of Kyushu University in Japan. In the study site, sika deer (Cervus nippon) have reduced understory vegetation since the 1990s, denuding it since the 2000s. Most of the recruitment in the second half of the study period (1996–2014) consisted of tree species that sika deer cannot consume, such as Illicium anisatum and Pieris japonica subsp. japonica. Smaller trees had higher mortality throughout the study period. Neighboring trees affected the tree mortality significantly in the first half of the study period (1984–1996), while they did not significantly affect it in the second half. However, neighboring trees significantly affected the growth rate of trees throughout study period. Based on our findings, we speculate that an increase in sika deer population may have affected the competition between individual trees in the mixed forest. The effects of tree size and neighboring trees on mortality and growth varied depending on the growth form groups and the species.
九州大学農学部附属宮崎演習林内の針広混交林において，樹木サイズと隣接個体の胸高断面積合計が樹木の成長と枯死に及ぼす影響を，シカの個体数が増加した30 年間の前期（1984-1996 年）と後期（1996-2014 年）とで比較した。本調査地では下層植生が1990 年代から衰退し，2000 年代ではほぼ消滅した。調査期間の後期に更新した樹木のほとんどは，シカが採食しないシキミとアセビであった。小径木は成長速度が遅く，枯死率が高い傾向が調査期間を通じて観察された。調査期間の前期では，隣接個体が枯死率に有意に影響を及ぼしていたが，後期では影響が見られなかった。一方，隣接個体の成長に及ぼす影響は調査期間を通じて観察された。以上の結果から，本調査地において，シカの個体数増加は樹木の個体間競争に影響を及ぼした可能性が示唆された。これらの影響は樹木の生活型や種によって異なっていた。show more
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