森林立地54（2），81〜92 2012

Jpn J For Environ 54 (2), 81–92, 2012

 

イヌブナ天然林皆伐後の針葉樹不成績造林地における

イヌブナの萌芽再生と更新木としての有用性

 

松本健太郎^１・逢沢峰昭^２・菊地陽太^３・松本陽介^４・大久保達弘^２

^１宇都宮大学大学院農学研究科森林科学専攻・^２宇都宮大学農学部森林科学科

^３王子木材緑化株式会社・^４独立行政法人森林総合研究所

 

本研究は，栃木県日光市のイヌブナ天然林皆伐後に造成された針葉樹人工林のうち，激甚なクマ剥ぎ被害を受けたヒノキ人工林と植栽針葉樹が成林せず広葉樹二次林となった林分の２つの不成績造林地において，皆伐，下刈り，除伐といった人為撹乱下におけるイヌブナの萌芽再生過程を明らかにし，イヌブナの天然更新木としての有用性を評価することを目的として，林分構造調査および成長解析を行った。イヌブナはいずれの不成績造林地においても，複数の萌芽幹からなる株構造を有していた。下刈りと複数回の除伐が行われたヒノキ人工林では，ヒノキが高木層で，イヌブナが低木層で優占していた。下刈り後に除伐が行われなかった広葉樹二次林では，高木層は主として先駆性のミズメ，ミズキおよびウリハダカエデが優占し，イヌブナは亜高木層から低木層で優占していた。広葉樹二次林におけるイヌブナの直径成長は，周囲の先駆性の広葉樹と比べて小さいものの，いずれの萌芽幹も被圧林冠下でゆっくりと成長していた。また，いずれの不成績造林地の亜高木・低木層においても，イヌブナに匹敵する優占度をもつ遷移後期種はほとんどみられなかった。これらのことから，イヌブナは皆伐とその後の人為攪乱下においても個体群の維持が可能な萌芽再生能力を保持し，将来的にイヌブナは主要な林冠構成樹種の１つになると考えられた。したがって，不成績造林地を針広混交林化あるいは広葉樹林化する場合には，イヌブナは天然更新木として有用な樹種であると考えられた。

キーワード：イヌブナ，人為撹乱下，萌芽再生，針葉樹不成績造林地，広葉樹林

 

Kentaro Matsumoto, Mineaki Aizawa, Yota Kikuchi, Yoosuke Matsumoto and Tatsuhiro Ohkubo：Sprout regeneration of Japanese beech (Fagus japonica) and its usefulness as a regenerator in unsuccessful conifer plantations after clear-cutting of natural Japanese beech forests. Japanese Journal of Forest Environment 54:81−92, 2012.

We aimed to delineate the regeneration process of Japanese beech (Fagus japonica) by sprouting under strong and frequent human-induced disturbances, such as clear-cutting, weeding, and salvage cutting, and to assess the usefulness of the species as a natural regenerating tree in unsuccessful conifer plantations after clear-cutting of natural Japanese beech forests in Nikko, Tochigi. We investigated the stand structures and analyzed the growth of Japanese beeches and their spatially neighboring trees, focusing on 2 types of unsuccessful conifer plantations, (1) the Hinoki cypress plantations where weeding and several salvage cuttings had been conducted, and which were degraded by the bark stripping by bears; and (2) secondary broad-leaved forests resulting from the poor growth of conifers planted in locations where weeding had been conducted. Japanese beech exhibited stool structures with many stems resulting from sprouting under all the human-induced disturbances mentioned above. In the Hinoki cypress plantations, Japanese beech was the most dominant species under the tree layer of cypresses; in secondary broad-leaved forests early successional species, such as Betula grossa, were dominant in the tree layer, under which Japanese beech was dominant in the shade. Besides Japanese beech, almost no late successional species was observed under the tree layer in all the types of plantations. Therefore, Japanese beech could maintain a strong ability to produce sprouts and survive in unsuccessful conifer plantations under human-induced disturbances, and might become a main tree-layer component in the future. If unsuccessful conifer plantations are converted to broad-leaved forests, Japanese beech would be the most useful natural regenerator among the surviving broad-leaved trees.

Keywords : broad-leaved forest, Fagus japonica, under human-induced disturbances, sprout regeneration, unsuccessful conifer plantation