Effects of Thinning and Litter Removal on the Recovery of Riparian Vegetation in a Cryptomeria Japonica Plantation

27 Mar Effects of Thinning and Litter Removal on the Recovery of Riparian Vegetation in a Cryptomeria Japonica Plantation

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Abstract

人工林から天然性の渓畔林への誘導を目的とし，渓畔域に位置するスギ人工林において間伐およびリター除去を行い，植物の定着との関係を調査した。発芽した出現種数，発生個体数，生残個体数は無処理区や巻き枯らし区よりも皆伐区や間伐区で多い傾向があった。リターを除去した方が発生個体数，出現種数ともに有意に多かった。また，渓畔林構成種の出現種数は増加したものの，フサザクラなどの一部の樹種が優占し，シオジやサワグルミなどの主要樹種はみられなかった。草本植物の渓畔林構成種はわずかしかみられなかった。伐採や林床処理によって天然更新が可能であると考えられたが，天然性渓畔林に近い林分へ誘導するためには，長期的な研究を行い，その結果によっては，一部の種の植栽や播種による導入も検討する必要がある。

English Abstract

The effects of thinning and litter removal treatments on the establishment of riparian vegetation were investigated in a Cryptomeria japonica plantation. The number of germi ted seedlings and species richness were significantly greater in the plots that were thinned (30% and more) than in the control or girdling plots. Litter removal also encouraged the germi tion of many species, resulting in greater numbers of seedlings and species. Thinning increased the number of component species of tural riparian forests. However, the established understory vegetation was domi ted by Euptelea polyandra, while Pterocarya rhoifolia and Fraxinus platypoda, the typical canopy trees of tural riparian forests, and several regio l riparian perennial herbs were absent. These results suggest the possibility of tural regeneration of riparian species in ma ged forests, and the need for long-term monitoring to establish optimal ma gement practices, including planting, for the restoration of semi- tural riparian forests.