森林立地学会誌　森林立地44(2), 2002, 37〜43

Jpn. J. For. environment44(2), 37-43 2002

関東平野におけるスギ林衰退と土壌要因

伊藤江利子^＊・吉永秀一郎^＊・大貫靖浩^＊・志知幸治^＊＊・松本陽介^＊・垰田　宏^＊＊＊

^＊森林総合研究所^＊＊・森林総合研究所東北支所

^＊＊＊森林総合研究所四国支所

関東平野におけるスギ林衰退の原因を解明するため，34地点の固定調査地でスギ林衰退度と土壌条件（母材，堆積様式，土性，表層0-8cm・次表層8-16cmの容積重，表層土壌孔隙率，有効土層深）との関係を検討した。衰退度は砂土が卓越する低地で高く，火山灰や堆積岩を母材とする埴壌土が卓越する台地および丘陵地で低い。容積重および孔隙率は衰退度と相関が認められ，表層土壌の物理的特性がスギ林衰退に影響を与えていた。また，表層土壌の堅密化の影響が有効土層深の深さによって緩和されることが示唆された。これらの検討の結果，強度のスギ林衰退は，土層厚が浅く，堅密な土壌で発生していることが明らかにされた。また，寺社境内では踏圧のため，表層が局所的に堅密化しており，そのような場所では極度の衰退が単木的に認められた。人為による土壌の物理性の悪化が，スギ衰退を助長していると考えられた。

Eriko Ito, Shuichiro Yoshinaga, Yasuhiro Ohnuki, Koji Shichi,Yoosuke Matsumoto and Hiroshi Taoda: Soil factors affecting the decline of Cryptomeria japonika forest in Kanto plains, Japan

The purpose of this study was to clarify the effect of soil factors on the decline of Clyptomeria japonica in Kanto plains. Soil features, such as parent material, types of deposition, soil texture, bulk density(soil depth: 0-8, 8-16 cm), porosity and hardness of surface soil were investigated in 34 study sites, where the decline index previously reported. The index performed damaged at lowland sites with sandy alluvial soil, although healthy at upland or hill sites with clayey or loamy soils derived from volcanic ash or weathering products of sedimentary rock. These results showed locations and parent materials affected to the tree decline. Furthermore, the remarkable correlation was observed between bulk density and the decline index. Thus, compact surface soil was correlated with the decline, however, thick soil layer eases the influence of compact surface soil. Most of sites were located in the grounds of temples and shrines. Extremely compact surface soil often occurred by treading, and trees were damaged. The forest decline was effected by soil factors relating to density and was accelerated by artificial impacts.