The Effect of Thinning on the Community Structure and Densities of Soil Animals in a Chamaecyparis Obtusa Plantation

27 Mar The Effect of Thinning on the Community Structure and Densities of Soil Animals in a Chamaecyparis Obtusa Plantation

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Abstract

ヒノキ人工林において, 間伐が林床の土壌動物相に与える影響を調査した。間伐され下層植生の繁茂する林分 (間伐区) と, 間伐がほとんど行われず下層植生の衰退した林分 (間伐遅れ区) において, 土壌動物の群集構成と個体数密度を比較した。両調査区のリター層と土壌層からサンプルを採取し, ツルグレン装置により土壌動物を抽出・分類した。その結果, 土壌動物の分類群数は, リター層・土壌層ともに間伐区よりも間伐遅れ区で有意に少なかった。また, 個体数で優占していたササラダニ亜目 (Oribatida), トビムシ目 (Collembola) の個体数密度は, リター層・土壌層ともに間伐区よりも間伐遅れ区で有意に低かった。以上の結果より, ヒノキ人工林では, 間伐施業の不足が土壌動物の群集構成を単純化させ, 個体数密度を低下させる可能性が示された。

English Abstract

In a Chamaecyparis obtusa plantation, we examined the effect of thinning on soil animal communities. The community composition and individual densities of soil animals were compared between a rich-understory plot with thinning ma gement (the thinned plot) and a poor understory plot without thinning (the delayed thinning plot). Soil animals sampled from both the litter and soil layers were classified after collection by the Tullgren method. In both layers, the taxa in the delayed thinning plot were significantly poorer than those in the thinned plot. The densities of oribatida mites and collembolans, both of which were domi nt taxa, were significantly lower in the delayed thinning plot than in the thinned plot for both litter and soil samples. Our results suggest that lack of ma gement of forests such as no thinning has a negative effect on the community composition and density of soil animals in the forest floor.